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There are several processes for making magnets, but the most common method is called Powder Metallurgy. In this process, a suitable composition is pulverized into fine powder, compacted and heated to cause densification via "liquid phase sintering". Therefore, these magnets are most often called sintered magnets. Ferrite, Samarium Cobalt ( SmCo) and neodymium-iron-boron ( neo) magnets are all made by this method. Unlike ferrite, which is a ceramic material, all of the rare earth magnets are metal alloys.

Suitable raw materials are melted under vacuum or inert gas in an induction melting furnace. The molten alloy is either poured into a mold, onto a chill plate, or processed in a strip caster - a device that forms a thin, continuous metal strip. These cured metal "chunks" are crushed and pulverized to form a fine powder ranging from 3 to 7 microns in diameter. This very fine powder is chemically reactive, capably of igniting spontaneously in air and therefore must be protected from exposure to oxygen.

There are several methods for compacting the powder and they all involve aligning the particles so that in the finished part all the magnetic regions are pointing in a prescribed direction. The first method is called axial or transverse pressing. This is where powder is placed into a cavity in a tool on the press and punches enter the tool to compress the powder. Just prior to compaction, an aligning field is applied. The compaction "freezes-in" this alignment. In axial (parallel) pressing, the aligning field is parallel to the direction of compaction. In transverse (perpendicular) pressing, the field is perpendicular to the compaction pressure. Because the small powder particles are elongated in the direction of magnetic alignment, transverse pressing yields better alignment, thus a higher energy product. Compacting powder in hydraulic or mechanical presses limits the shape to simple cross-sections that can be pushed out of the die cavity.

A second compaction method is called isostatic pressing wherein a flexible container is filled with powder, the container is sealed, an aligning field is applied, and the container is placed into the isostatic press. Using a fluid, either hydraulic fluid or water, pressure is applied to the outside of the sealed container, compacting it equally on all sides. The main advantages to making magnet blocks via isostatic pressing is that very large blocks can be made - frequently up to 100 x 100 x 250 mm and since pressure is applied equally on all sides, the powder remains in good alignment producing the highest possible energy product.

Pressed parts are packaged in "boats" for loading into a vacuum sintering furnace. The particular temperatures and presence of vacuum or inert gas is specific to the type and grade of magnet being produced. Both rare earth materials are heated to a sintering temperature and allowed to densify. SmCo has the additional requirement of a "solutionizing" treatment after sintering. After reaching room temperature, both materials are given a lower temperature tempering heat treatment. During sintering, the magnets shrink about 15-20% linearly. Completed magnets have a rough surface and only approximate dimensions. They also exhibit no external magnetic field.

Finishing

Sintered magnets receive some degree of machining which can range from grinding them smooth and parallel, OD or ID grinding, or slicing block magnets into smaller parts. The magnet material is both brittle and very hard (Rockwell C 57 to 61) and requires diamond wheels for slicing and diamond or special abrasive wheels for grinding. Slicing can be performed with excellent precision often eliminating the need for subsequent grinding. All of these processes must be conducted very carefully to minimize chipping and cracking.

In some cases, the final magnet shape is conducive to processing with a shaped diamond grinding wheel such as arcs and bread loafs. Product in approximate final shape is fed past the grinding wheel which provides the precise dimensions. For lower volume manufacturing of these complex shapes, EDM machining is commonly used. Simple two-dimensional profiles, EDM is faster while more complex shapes using 3-5 axis machines run slower.

Cylindrical parts may be pressed-to-shape, usually axially, or core-drilled from block stock material. These longer cylinders, either solid or with an ID, can later be sliced to form thin washer-shaped magnets.

For large volume manufacture, typically 5,000 or more pieces, it is usually more economical to make tooling and produce to shape. For short-runs or for specific properties, it may be preferred to machine magnets from block. When pressing-to-shape, material scrap, such as grind swarf is minimized. Order quantity, part shape, size and complexity will all contribute to the decision as to which manufacturing method is preferable. Delivery time will also affect the decision as making limited quantities from stock blocks is likely faster than ordering tooling for press-to-shape parts. Costing these options is not always straight-forward. It is recommended to contact us to discuss options.

Although intricate magnet shapes can be produced from these alloys, the materials are best suited for simpler shapes. Holes, large chamfers or slots are more costly to produce. Tolerances are more difficult to hold on more complex shapes which are likely to result in flux field variations and potential physical stressing of the part in an assembly.

Machined magnets will have sharp edges which are prone to chipping. Coating around a sharp edge is also problematic. The most common method for reducing the sharpness is a vibratory hone, often called vibratory tumbling and done in an abrasive media. The specified rounding of the edge depends upon subsequent processing and handling requirements but is most often 0.005" to 0.015" (0.127 to 0.38 mm) radius.

Neo magnets, which are prone to rusting or reacting chemically, are almost always coated. Samarium cobalt is naturally more corrosion resistant than neo, but does, on occasion benefit from coating. The most common protective coatings include dry-sprayed epoxy, e-coat (epoxy), electrolytic nickel, aluminum IVD, and combinations of these coatings. Magnets can also be coated with conversion coatings such as zinc, iron or manganese phosphates and chromates. Conversion coatings are generally adequate for temporary protection and can form an under-layer for epoxy coating or an over layer to enhance protection from aluminum IVD.

After the manufacturing is completed, the magnet requires " charging" to produce an external magnetic field. This can be accomplished in a solenoid - a hollow cylinder into which various magnet sizes and shapes can be placed - or with fixtures designed to impart unique magnetic patterns. It is also possible to magnetize large assemblies to avoid handling and assembling these powerful magnets in their magnetized condition. The magnetizing field requirements are substantial. This, as many other aspects of magnet selection, should be discussed with our engineering and production team.

In some instances magnets will require stabilization or calibration. Stabilization is a process of pre-treating the magnets, in or out of an assembly, so that subsequent use will not result in additional loss of flux output. Calibration is performed to narrow the performance output range of a group of magnets. These processes require treating in an oven at elevated temperature or reverse pulsing in a magnetizer at fields below full knock-down power. There are several factors that affect thermal stabilization and it is important that this process is controlled very carefully to ensure proper final product performance.

Contact us with your questions or comments.

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There are several processes for making magnets, but the most common method is called Powder Metallurgy. In this process, a suitable composition is pulverized into fine powder, compacted and heated to cause densification via "liquid phase sintering". Therefore, these magnets are most often called sintered magnets.

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Supercool Superconductor Makes Magnet "Magically" Float

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Magnets naturally levitate above superconductors. The magnet's magnetic field can't penetrate the superconductor, causing it to float almost magically above. See this phenomenon at work in an exclusive Scientific American video.

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Everything you wanted to know about Magnets

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'How Magnet Works - The FORCE of Nature | A Documentary Film' on ViewPure

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How Magnet Works - The FORCE of Nature | A Documentary Film\n\nMagnet - is a product or item that creates a magnetic field strength.

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'Richard Garriott Space Video Blog: Magnetism' on ViewPure

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Richard Garriott demonstrates how magnets act in space using two magnets to see if, in microgravity, they interact with each other the same way they do on the surface of the Earth; if magnetic forces act at a distance; and where do they point. Magnetism is one of the fundamental forces.

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Magnetism-Great launch point for several cool magnet ideas

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Magnetism-Great launch point for several cool magnet ideas

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Magnetism is the force exerted by magnets when they attract or repel each other. Magnetism is caused by the motion of electric charges.

Every substance is made up of tiny units called atoms. Each atom has electrons, particles that carry electric charges. Spinning like tops, the electrons circle the nucleus, or core, of an atom. Their movement generates an electric current and causes each electron to act like a microscopic magnet.

In most substances, equal numbers of electrons spin in opposite directions, which cancels out their magnetism. That is why materials such as cloth or paper are said to be weakly magnetic. In substances such as iron, cobalt, and nickel, most of the electrons spin in the same direction. This makes the atoms in these substances strongly magnetic-but they are not yet magnets.

To become magnetized, another strongly magnetic substance must enter the magnetic field of an existing magnet. The magnetic field is the area around a magnet that has magnetic force.

All magnets have north and south poles. Opposite poles are attracted to each other, while the same poles repel each other. When you rub a piece of iron along a magnet, the north-seeking poles of the atoms in the iron line up in the same direction. The force generated by the aligned atoms creates a magnetic field. The piece of iron has become a magnet.

Some substances can be magnetized by an electric current. When electricity runs through a coil of wire, it produces a magnetic field. The field around the coil will disappear, however, as soon as the electric current is turned off.

Geomagnetic Poles

The Earth is a magnet. Scientists do not fully understand why, but they think the movement of molten metal in the Earth's outer core generates electric currents. The currents create a magnetic field with invisible lines of force flowing between the Earth's magnetic poles.

The geomagnetic poles are not the same as the North and South Poles. Earth's magnetic poles often move, due to activity far beneath the Earth's surface. The shifting locations of the geomagnetic poles are recorded in rocks that form when molten material called magma wells up through the Earth's crust and pours out as lava. As lava cools and becomes solid rock, strongly magnetic particles within the rock become magnetized by the Earth's magnetic field. The particles line up along the lines of force in the Earth's field. In this way, rocks lock in a record of the position of the Earth's geomagnetic poles at that time.

Strangely, the magnetic records of rocks formed at the same time seem to point to different locations for the poles. According to the theory of plate tectonics, the rocky plates that make up the Earth's hard shell are constantly moving. Thus, the plates on which the rocks solidified have moved since the rocks recorded the position of the geomagnetic poles. These magnetic records also show that the geomagnetic poles have reversed-changed into the opposite kind of pole-hundreds of times since the Earth formed.

Earth's magnetic field does not move quickly or reverse often. Therefore, it can be a useful tool for helping people find their way around. For hundreds of years, people have used magnetic compasses to navigate using Earth's magnetic field. The magnetic needle of a compass lines up with Earth's magnetic poles. The north end of a magnet points toward the magnetic north pole.

Earth's magnetic field dominates a region called the magnetosphere, which wraps around the planet and its atmosphere. Solar wind, charged particles from the sun, presses the magnetosphere against the Earth on the side facing the sun and stretches it into a teardrop shape on the shadow side.

The magnetosphere protects the Earth from most of the particles, but some leak through it and become trapped. When particles from the solar wind hit atoms of gas in the upper atmosphere around the geomagnetic poles, they produce light displays called auroras. These auroras appear over places like Alaska, Canada and Scandinavia, where they are sometimes called " Northern Lights." The " Southern Lights " can be seen in Antarctica and New Zealand.

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Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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Magnetism is the force exerted by magnets when they attract or repel each other. Magnetism is caused by the motion of electric charges. Every substance is made up of tiny units called atoms. Each atom has electrons, particles that carry electric charges. Spinning like tops, the electrons circle the nucleus, or core, of an atom.

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More Magnet Basics

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'MAGNETS: How Do They Work?' on ViewPure

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The Conquest Continues over on Veritasium: http://bit.ly/VEMagnets_m\n\nTHANK YOU to our amazing Subbable.com subscribers whose donations help keep MinutePhysics running!\nCalvin Kennell-Heiling\nBendik Åshaug Holm\nMatthew Joseph Woolley\nTheTripleBstudios - http://www.youtube.com/TheTripleBstudios\nMike Ledermueller\nMark Liederbach - https://plus.google.com/112637595591573891595/posts\nStephanie Ahlberg-Rosell - scoutingwithmeurr.wordpress.com\nK. Repking\n@lifeasasleeper\n\nHow do magnets work? Why do they attract and repel at long distances? Is it magic? No...

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by Chris Woodford. Last updated: September 26, 2018.

Science is our understanding of how the world works-and generally the world works fine whether we understand it or not. Take magnetism, for example. People have known about magnets for thousands of years and they've been using them practically, as compasses, for almost as long. The ancient Greeks and Romans knew as well as we do that lodestone (an iron-rich mineral) can attract other pieces of iron, while the ancient Chinese were making magnetic compasses set in intricate wooden inlays for their practice of Feng Shui (the art of carefully arranging a room) thousands of years before interior designers came on board. Science can sometimes be slow to catch up: we've only really learned how magnetism works in the last century, since the world inside atoms was first discovered and explored.

Photo: A typical horseshoe magnet. See the trace of brown rust on the top of the magnet's upper "leg"? That happens because the magnet is made of iron, which corrodes (rusts) in damp air.

What is magnetism?

Photo: The magnetic field between the opposite poles of two bar magnets that strongly attract one another. We can't normally see magnetic fields, but if you sprinkle iron filings (tiny bits shaved off an iron bar with a file) onto a piece of paper and hold it above the magnets you can see the field underneath. Photo by courtesy of Wikimedia Commons (where you'll find a bigger version of this image).

Playing with magnets is one of the first bits of science most children discover. That's because magnets are easy to use, safe, and fun. They're also quite surprising. Remember when you first discovered that two magnets could snap together and stick like glue? Remember the force when you held two magnets close and felt them either attract (pull toward one another) or repel (push away)? One of the most amazing things about magnets is the way they can attract other magnets (or other magnetic materials) "at a distance," invisibly, through what we call a magnetic field.

To ancient people, magnetism must have seemed like magic. Thousands of years down the line, we understand what happens inside magnetic materials, how their atomic structure causes their magnetic properties, and how electricity and magnetism are really just two sides of the same coin: electromagnetism. Once scientists would have said magnetism was the strange, invisible force of attraction between certain materials; today, we're more likely to define it as a force created by electric currents (themselves caused by moving electrons).

SIX things to know about magnets

Almost everyone knows these six basic facts about how magnets behave:

1. A magnet has two ends called poles, one of which is called a north pole or north-seeking pole, while the other is called a south pole or south-seeking pole.

2. The north pole of one magnet attracts the south pole of a second magnet, while the north pole of one magnet repels the other magnet's north pole. So we have the common saying: like poles repel, unlike poles attract.

3. A magnet creates an invisible area of magnetism all around it called a magnetic field.

4. The north pole of a magnet points roughly toward Earth's north pole and vice-versa. That's because Earth itself contains magnetic materials and behaves like a gigantic magnet.

5. If you cut a bar magnet in half, it's a bit like cutting an earthworm in half! You get two brand new, smaller magnets, each with its own north and south pole. (This is, of course, a joke. You don't get two worms if you cut a worm in half. But you do get two magnets.)

6. If you run a magnet a few times over an unmagnetized piece of a magnetic material (such as an iron nail), you can convert it into a magnet as well. This is called magnetization.

What is a magnetic field?

Photo: A colorful way to visualize invisible magnetic fields using a computer graphics program developed at Los Alamos National Laboratory. In this three-dimensional chart, the height and color of the peaks shows the strength of the magnetic field at each point. Photo by courtesy of US Department of Energy.

Suppose you put a bar magnet (shaped like a rectangle, sometimes with the north and south poles painted different colors) or a horseshoe magnet (bent round into a tight U-shape) onto a table and place an iron nail nearby. If you push the magnet slowly toward the nail, there will come a point when the nail jumps across and sticks to the magnet. That's what we mean by magnets having an invisible magnetic field that extends all around them. Another way of describing this is to say that a magnet can "act at a distance": it can cause a pushing or pulling force on other objects it isn't actually touching).

Magnetic fields can penetrate through all kinds of materials, not just air. You probably have little notes stuck to the door of your refrigerator with brightly colored magnets-so you can see that magnetic fields cut through paper. You may have done the trick where you use a magnet to pick up a long chain of paperclips, with each clip magnetizing the next one along. That little experiment tells us that a magnetic field can penetrate through magnetic materials such as iron.

Earth the Magnet

Why do magnets point north or south? A great English scientist named William Gilbert answered that question in 1600 when he suggested that Earth is a giant magnet.

Photo: We can use magnetic compasses like this to navigate because Earth is itself a giant magnet. Photo by Staff Sgt. Jacob N. Bailey courtesy of US Air Force.

Gilbert's theory was published in De Magnete (Of Magnets, Magnetic Bodies, and the Great Magnet of the Earth), the first big scientific book published in the English language (previously, scientific books had always been written in Latin). Like all true scientists, Gilbert tested many of his ideas with careful experiments.

We now know that Earth is magnetic because it's packed with molten rocks rich in magnetic materials such as iron. Just like a bar magnet, Earth's magnetic field stretches out into space, in a region called the magnetosphere, and can affect things around it. When energetic particles zooming in from the Sun (the so-called solar wind) interact with Earth's magnetic field, we get amazing auroras in the sky (the northern lights or aurora borealis and the southern lights or aurora australis).

Photo: The Northern Lights above Bear Lake, Alaska. Photo by Senior Airman Joshua Strang courtesy of US Air Force.

What about other stars and planets-do they have magnetism too? We know the Sun has a magnetic field several times stronger than Earth's, but the Moon has little or no magnetism. The other planets have magnetic fields too. Saturn, Jupiter, Neptune, and Uranus have fields stronger than Earth's, while Mars, Mercury, and Venus have weaker fields. It's not yet known whether Pluto has a magnetic field (but then astronomers are still arguing over whether it's even a planet!).

How can we measure magnetism?

The strength of the field around a magnet depends on how close you get: it's strongest very near the magnet and falls off quickly as you move away. (That's why a small magnet on your table has to be quite close to things to attract them.) We measure the strength of magnetic fields in units called gauss and tesla (the modern SI unit, named for Croatian-born US electricity pioneer Nikola Tesla, 1856-1943). It's interesting to note that the strength of Earth's magnetic field is very weak-about 100-1000 times weaker than that of a typical bar or fridge magnet. On Earth, gravity, not magnetism, is the force that sticks you to the floor. We'd notice Earth's magnetism much more if its gravity weren't so very strong.

Chart: Comparing the strength of some "everyday" sources of magnetism. Please note that the vertical scale is logarithmic: each step up the scale means the strength of the magnetic field has increased ten times. The main thing to note here is how very weak Earth's magnetism is (the green block on the extreme left) compared to everything else we routinely encounter (never mind the giant magnets used in hospitals and labs). The record-breaking lab magnetic field shown on the extreme right, created in Japan in April 2018, is about 24 million times stronger than Earth's magnetic field. My data for this chart comes from the following sources: Earth (goo.gl/TkxfO3), Sun (goo.gl/8uigAU), appliances (goo.gl/P3l487), fridge (goo.gl/OhrDKt), small neodymium (goo.gl/avODib), junkyard (goo.gl/owWZer), MRI (goo.gl/jQ8cTD), loudspeaker (goo.gl/oIwNlS), biggest MRI (goo.gl/8zkACY), biggest lab (bit.ly/2zvH7On). Almost everything produces magnetism-even our own bodies, which make something like a puny 0.000000001 tesla.

What is an electromagnet?

The Homer Simpson or Mickey Mouse magnet that holds things to your refrigerator is a permanent magnet: it keeps hold of its magnetism all the time. Not all magnets work this way. You can make a temporary magnet by passing electricity through a coil of wire wrapped around an iron nail (a device you'll sometimes see referred to as a solenoid). Switch on the current and the nail becomes a magnet; switch it off again and the magnetism disappears. (This is the basic idea behind an electric chime doorbell: you make an electromagnet when you press the button, which pulls a hammer onto the chime bar-ding-dong!) Temporary magnets like this are called electromagnets -magnets worked by electricity-and they hint at a deeper connection between electricity and magnetism that we'll come on to in a moment.

Like permanent magnets, temporary electromagnets come in different sizes and strengths. You can make an electromagnet powerful enough to pick up paperclips with a single 1.5-volt battery. Use a much bigger voltage to make a bigger electric current and you can build an electromagnet powerful enough to pick up a car. That's how scrapyard electromagnets work. The strength of an electromagnet depends on two main things: the size of the electric current you use and the number of times you coil the wire. Increase either or both of these and you get a more powerful electromagnet.

Magnetism and electricity: the theory of electromagnetism

Electromagnets show that you can make magnetism using electricity. In fact, as European scientists discovered in the 19th century, electricity always makes magnetism when it moves about or changes. Every time an electric current flows in a wire, it generates a magnetic field all around it. Changing electricity, in short, produces magnetism.

Photo: The father of electromagnetism, James Clerk Maxwell. Public domain photo by courtesy of Wikimedia Commons.

The reverse is true as well: you can make electricity using a changing pattern of magnetism. That's just as well or you wouldn't be reading these words now. Virtually all the electricity we use (with the exception of electricity produced from solar cells) is made by devices called generators. These use powerful magnets and coils of wire to produce electricity with the help of turbines, devices that capture kinetic energy from fluids that move past them (typically wind, water, or steam made from coal, oil, or nuclear power).

How do you get electricity from magnetism? Simply speaking, you put a metal wire near a magnet (so the wire is inside the magnetic field). Move the wire or move the magnet so the magnetic field inside the wire fluctuates and electricity will flow through the wire. Keep moving the wire or magnet and you'll make electricity continually.

You can see from this that electricity and magnetism are partners. Wherever you find one, the other is never far away. The first person to explain this properly, in the mid-19th century, was a brilliant Scottish physicist named James Clerk Maxwell. His theory summed up everything then known about electricity and magnetism in four relatively simple mathematical formulas. Maxwell's equations, as we now call them, combined electricity and magnetism into a single, powerful theory we call electromagnetism. We now know that electromagnetism is one of the four fundamental forces that control everything that happens in our universe-and that's a powerful idea indeed!

What use are magnets?

Maybe you think magnets are interesting; maybe you think they're boring! What use are they, you might ask, apart from in childish magic tricks and scrapyards?

You might be surprised just how many things around you work by magnetism or electromagnetism. Every electric appliance with an electric motor in it (everything from your electric toothbrush to your lawn mower) uses magnets to turn electricity into motion. Motors use electricity to generate temporary magnetism in wire coils. The magnetic field thus produced pushes against the fixed field of a permanent magnet, spinning the inside part of the motor around at high speed. You can harness this spinning motion to drive all kinds of machines.

There are magnets in your refrigerator holding the door closed. Magnets read and write data (digital information) on your computer's hard drive and on cassette tapes in old-fashioned personal stereos. More magnets in your hi-fi loudspeakers or headphones help to turn stored music back into sounds you can hear. If you're sick with a serious internal illness, you might have a type of body scan called NMR (nuclear magnetic resonance), which draws the world beneath your skin using patterns of magnetic fields. Magnets are used to recycle your metal trash ( steel food cans are strongly magnetic but aluminum drinks cans are not, so a magnet is an easy way to separate the two different metals).

Photo: An NMR scan like this builds up a detailed image of a patient's body (or, in this case, their head) on a computer screen using the magnetic activity of atoms in their body tissue. You can see the patient going into the scanner at the top and the image of their head on the screen below. Photo by courtesy of Warren Grant Magnuson Clinical Center (CC) and US National Institutes of Health (NIH).

Which materials are magnetic?

Iron is the king of magnetic materials-the metal we all think of when we think of magnets. Most other common metals (such as copper, gold, silver, and aluminum) are, at first sight, nonmagnetic and most nonmetals (including paper, wood, plastic, concrete, glass, and textiles such as cotton and wool) are nonmagnetic too. But iron's not the only magnetic metal. Nickel, cobalt, and elements that belong to a part of the Periodic Table (the orderly arrangement chemists use to describe all the known chemical elements) known as the rare-Earth metals (notably samarium and neodymium) also make good magnets. Some of the best magnets are alloys (mixtures) of these elements with one another and with other elements. Ferrites (compounds made of iron, oxygen, and other elements) also make superb magnets. Lodestone (which is also called magnetite) is an example of a ferrite that's commonly found inside Earth (it has the chemical formula FeO·Fe2O3).

Materials like iron turn into good temporary magnets when you put a magnet near them, but tend to lose some or all of their magnetism when you take the magnet away again. We say these materials are magnetically soft. By contrast, alloys of iron and the rare-Earth metals retain most of their magnetism even when you remove them from a magnetic field, so they make good permanent magnets. We call those materials magnetically hard.

Is it true to say that all materials are either magnetic or nonmagnetic? People used to think that but scientists now know that the materials we consider to be nonmagnetic are also affected by magnetism, though extremely weakly. The extent to which a material can be magnetized is called its susceptibility.

How different materials react to magnetism

Scientists have a number of different words to describe how materials behave when you put them near a magnet (which is another way of saying when you put them inside a magnetic field). Broadly speaking, we can divide all materials into two kinds called paramagnetic and diamagnetic, while some of the paramagnetic materials are also ferromagnetic. It's important to be clear what these confusing words actually mean...

Paramagnetic

Make a sample of a magnetic material and hang it from a thread so it dangles in a magnetic field, and it will magnetize and line itself up so its magnetism is parallel to the field. As people have known for thousands of years, this is how exactly a compass needle behaves in Earth's magnetic field. Materials that behave this way are called paramagnetic. Metals such as aluminum and most nonmetals (which you might think aren't magnetic at all) are actually paramagnetic, but so weakly that we don't notice. Paramagnetism depends on temperature: the hotter a material is, the less it's likely to be affected by nearby magnets.

Photo: We think of aluminum (used in drinks cans like these) as nonmagnetic. That helps us separate for recycling our aluminum cans (which don't stick to magnets) from our steel ones (which do). In fact, both materials are magnetic. The difference is that aluminum is very weakly paramagnetic, while steel is strongly ferromagnetic. Photo courtesy of US Air Force.

Ferromagnetic

Some paramagnetic materials, notably iron and the rare-Earth metals, become strongly magnetized in a field and usually stay magnetized even when the field is removed. We say materials like this are ferromagnetic, which really just means they're "magnetic like iron." However, a ferromagnetic material will still lose its magnetism if you heat it above a certain point, known as its Curie temperature. Iron has a Curie temperature of 770°C (1300°F), while for nickel the Curie temperature is ~355°C (~670°F). If you heat an iron magnet to 800°C (~1500°F), it stops being a magnet. You can also destroy or weaken ferromagnetism if you hit a magnet repeatedly.

Diamagnetic

We can think of paramagnetic and ferromagnetic materials as being "fans" of magnetism: in a sense, they "like" magnetism and respond positively to it by allowing themselves to be magnetized. Not all materials respond so enthusiastically. If you hang some materials in magnetic fields, they get quite worked up inside and resist: they turn themselves into temporary magnets to resist magnetization and weakly repel magnetic fields outside themselves. We call these materials diamagnetic. Water and lots of organic (carbon-based) substances, such as benzene, behave this way. Tie a diamagnetic material to a thread and hang it in a magnetic field and it will turn so it makes an angle of 180° to the field.

What causes magnetism?

In the early 20th century, before scientists properly understood the structure of atoms and how they work, they came up with an easy-to-understand idea called the domain theory to explain magnetism. A few years later, when they understood atoms better, they found the domain theory still worked but could itself be explained, at a deeper level, by the theory of atoms. All the different aspects of magnetism we observe can be explained, ultimately, by talking about either domains, electrons in atoms, or both. Let's look at the two theories in turn.

Explaining magnetism with the domain theory

Imagine a factory somewhere that makes little bar magnets and ships them out to schools for their science lessons. Picture a guy called Dave who has to drive their truck, transporting lots of cardboard boxes, each one with a magnet inside it, to a different school. Dave doesn't have time to worry which way the boxes are stacked, so he piles them inside his truck any old how. The magnet inside one box could be pointing north while the one next to it is pointing south, east, or west. Overall, the magnets are all jumbled up so, even though magnetic fields leak out of each box, they all cancel one another out.

The same factory employs another truck driver called Bill who couldn't be more different. He likes everything tidy, so he loads his truck a different way, stacking all the boxes neatly so they line up exactly the same way. Can you see what will happen? The magnetic field from one box will align with the field from all the other boxes... effectively turning the truck into one giant magnet. The cab will be like a giant north pole and the back of the truck a huge south pole!

What happens inside these two trucks is what happens on a tiny scale inside magnetic materials. According to the domain theory, something like an iron bar contains lots of tiny pockets called domains. Each domain is a bit like a box with a magnet inside. See where we're heading? The iron bar is just like the truck. Normally, all its onboard "boxes" are arranged randomly and there's no overall magnetism: the iron is not magnetized. But arrange all the boxes in order, make them all face the same way, and you get an overall magnetic field: hey presto, the bar is magnetized. When you bring a magnet up to an unmagnetized iron bar and stroke it systematically and repeatedly up and down, what you're doing is rearranging all the magnetic "boxes" (domains) inside so they point the same way.

Domain theory explains what happens inside materials when they are magnetized. In an unmagnetized material (left), the domains are randomly arranged so there is no overall magnetic field. When you magnetize a material (right), by stroking a bar magnet over it repeatedly in the same direction, the domains rearrange so their magnetic fields align, producing a combined magnetic field in the same direction.

This theory explains how magnetism can arise, but can it explain some of the other things we know about magnets? If you chop a magnet in half, we know you get two magnets, each with a north and south pole. That makes sense according to the domain theory. If you cut a magnet in half, you get a smaller magnet that's still packed with domains, and these can be arranged north-south just like in the original magnet. What about the way magnetism disappears when you hit a magnet or heat it? That can be explained too. Imagine the van full of orderly boxes again. Drive it erratically, at really high speed, and it's a bit like shaking or hammering it. All the boxes will jumble up so they face different ways and the overall magnetism will disappear. Heating a magnet agitates it internally and jumbles up the boxes in much the same way.

Explaining magnetism with the atomic theory

The domain theory is easy enough to understand, but it's not a complete explanation. We know that iron bars aren't full of boxes packed with little magnets-and, if you think about, trying to explain a magnet by saying it's full of smaller magnets isn't really an explanation at all, because it immediately prompts the question: what are the smaller magnets made of? Fortunately, there's another theory we can turn to.

Back in the 19th century, scientists discovered they could use electricity to make magnetism and magnetism to make electricity. James Clerk Maxwell said that the two phenomena were really different aspects of the same thing-electromagnetism-like two sides of the same piece of paper. Electromagnetism was a brilliant idea, but it was more of a description than an explanation: it showed how things were rather than explaining why they were that way. It wasn't until the 20th century, when later scientists came to understand the world inside atoms, that the explanation for electromagnetism finally appeared.

We know everything is made of atoms and that atoms are made up of a central lump of matter called the nucleus. Minute particles called electrons move around the nucleus in orbit, a bit like satellites in the sky above us, but they also spin on their axis at the same time (just like spinning tops). We know electrons carry electric currents (flows of electricity) when they move through materials such as metals. Electrons are, in a sense, tiny particles of electricity. Now back in the 19th century, scientists knew that moving electricity made magnetism. In the 20th century, it became clear that magnetism was caused by electrons moving inside atoms and creating magnetic fields all around them. Domains are actually groups of atoms in which spinning electrons produce an overall magnetic field pointing one way or another.

Artwork: Magnetism is caused by electrons orbiting and spinning inside atoms. Note that this picture is not drawn to scale: most of an atom is empty space and the electrons are actually much further from the nucleus than I've drawn here.

Like the domain theory, atomic theory can explain many of the things we know about magnets, including paramagnetism (the way magnetic materials line up with magnetic fields). Most of the electrons in an atom exist in pairs that spin in opposite directions, so the magnetic effect of one electron in a pair cancels out the effect of its partner. But if an atom has some unpaired electrons (iron atoms have four), these produce net magnetic fields that line up with one another and turn the whole atom into a mini magnet. When you put a paramagnetic material such as iron in a magnetic field, the electrons change their motion to produce a magnetic field that lines up with the field outside.

What about diamagnetism? In diamagnetic materials, there are no unpaired electrons, so this doesn't happen. The atoms have little or no overall magnetism and are less affected by outside magnetic fields. However, the electrons orbiting inside them are electrically charged particles and, when they move in a magnetic field, they behave like any other electrically charged particles in a magnetic field and experience a force. That changes their orbits very slightly, producing some net magnetism that opposes the very thing that causes it (according to the classic bit of electromagnetic theory know as Lenz's law, which is related to the law of conservation of energy). As a result, the weak magnetic field they produce opposes the magnetic field that causes it-which is exactly what we see when diamagnetic materials try to "fight" the magnetic field they're placed in.

A brief history of magnetism

Ancient world: Magnetism is known to the ancient Greeks, Romans, and Chinese. The Chinese use geomantic compasses (ones with wooden inscriptions arranged in rings around a central magnetic needle) in Feng Shui. Magnets gain their name from Manisa in Turkey, a place once named Magnesia, where magnetic lodestone was found in the ground.

13th century: Magnetic compasses are first used for navigation in western nations. Frenchman Petrus Perigrinus (also called Peter of Maricourt) makes the first proper studies of magnetism.

17th century: English physician and scientist William Gilbert (1544-1603) publishes On Magnets, his monumental scientific study of magnetism, and proposes that Earth is a giant magnet.

18th century: Englishman John Michell (1724-93) and FrenchmanCharles Augustin de Coulomb (1736-1806) study the forces magnets can exert. Coulomb also makes important studies of electricity, but fails to connect electricity and magnetism as parts of the same underlying phenomenon.

19th century: Danishman Hans Christian Oersted (1777-1851), FrenchmenAndré-Marie Ampère (1775-1836) andDominique Arago (1786-1853), and EnglishmanMichael Faraday (1791-1867) explore the close connections between electricity and magnetism.James Clerk Maxwell (1831-1879) publishes a relatively complete explanation of electricity and magnetism (the theory of electromagnetism) and suggests electromagnetic energy travels in waves (paving the way for the invention ofradio).Pierre Curie (1859-1906) demonstrates that materials lose their magnetism above a certain temperature (now known as the Curie temperature).Wilhelm Weber (1804-1891) develops practical methods for detecting and measuring the strength of a magnetic field.

20th century: Paul Langevin (1872-1946) elaborates on Curie's work with a theory explaining how magnetism is affected by heat. French physicistPierre Weiss (1865-1940) proposes there are particles called magnetrons, equivalent to electrons, that cause the magnetic properties of materials and outlines the theory of magnetic domains. Two American scientists,Samuel Abraham Goudsmit (1902-78) andGeorge Eugene Uhlenbeck (1900-88), show how magnetic properties of materials result from the spinning motion of electrons inside them.

Find out more

On this website

We have lots of other articles related to magnetism-and the things that use it, including:

Books

For younger readers

For older readers

Hidden Attraction: The History and Mystery of Magnetism by Gerrit L. Verschuur. Oxford University Press, 2013. More history than mystery, thank goodness, and well worth a read.

The Man Who Changed Everything by Basil Mahon, John Wiley, 2003. A readable and easy-to-understand introduction to James Clerk Maxwell's life and work.

Electricity and Magnetism by W.J. Duffin. McGraw Hill, 2001. A brilliantly clear undergraduate text (and the one I used as a physics student).

James Clerk Maxwell by James R. Newman, Scientific American, 1955. Quite an old article, but still worth reading. It's an excellent summary of Maxwell's life as a mathematical physicist and explains very vividly how he visualized electromagnetism before figuring out the math behind it. [Subscription/payment]

De Magnete by William Gilbert, Chiswick Press, 1600. Thanks to Project Gutenberg, you can read the whole text of Gilbert's book online.

Videos

What is the magnetic field? by David Colarusso. A good, clear introduction to magnetic fields and how to draw them with magnetic field lines (2.5 minutes).

MIT: 8.02: Electricity and Magnetism by Walter Lewin. A much more detailed undergraduate course from the inspiring Dutch-born MIT physics professor (48 minutes), including some fun demonstrations.

Articles

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Magnetism for kids - A simple introduction

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by Chris Woodford. Last updated: September 26, 2018. Science is our understanding of how the world works-and generally the world works fine whether we understand it or not. Take magnetism, for example. People have known about magnets for thousands of years and they've been using them practically, as compasses, for almost as long.

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Magnetism-More Advanced

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Iron filings attracted to a horseshoe magnet show the magnetic field.

Credit: Milan B | Shutterstock

Magnetism is one aspect of the combined electromagnetic force. It refers to physical phenomena arising from the force caused by magnets, objects that produce fields that attract or repel other objects.

A magnetic field exerts a force on particles in the field due to the Lorentz force, according to Georgia State University's HyperPhysics website. The motion of electrically charged particles gives rise to magnetism. The force acting on an electrically charged particle in a magnetic field depends on the magnitude of the charge, the velocity of the particle, and the strength of the magnetic field.

All materials experience magnetism, some more strongly than others. Permanent magnets, made from materials such as iron, experience the strongest effects, known as ferromagnetism. With rare exception, this is the only form of magnetism strong enough to be felt by people.

Magnetic fields are generated by rotating electric charges, according to HyperPhysics. Electrons all have a property of angular momentum, or spin. Most electrons tend to form pairs in which one of them is "spin up" and the other is "spin down," in accordance with the Pauli Exclusion Principle, which states that two electrons cannot occupy the same energy state at the same time. In this case, their magnetic fields are in opposite directions, so they cancel each other. However, some atoms contain one or more unpaired electrons whose spin can produce a directional magnetic field. The direction of their spin determines the direction of the magnetic field, according to the Non-Destructive Testing (NDT) Resource Center. When a significant majority of unpaired electrons are aligned with their spins in the same direction, they combine to produce a magnetic field that is strong enough to be felt on a macroscopic scale.

Magnetic field sources are dipolar, having a north and south magnetic pole. Opposite poles (N and S) attract, and like poles (N and N, or S and S) repel, according to Joseph Becker of San Jose State University. This creates a toroidal, or doughnut-shaped field, as the direction of the field propagates outward from the north pole and enters through the south pole.

The Earth itself is a giant magnet. The planet gets its magnetic field from circulating electric currents within the molten metallic core, according to HyperPhysics. A compass points north because the small magnetic needle in it is suspended so that it can spin freely inside its casing to align itself with the planet's magnetic field. Paradoxically, what we call the Magnetic North Pole is actually a south magnetic pole because it attracts the north magnetic poles of compass needles.

If the alignment of unpaired electrons persists without the application of an external magnetic field or electric current, it produces a permanent magnet. Permanent magnets are the result of ferromagnetism. The prefix "ferro" refers to iron because permanent magnetism was first observed in a form of natural iron ore called magnetite, Fe ₃O ₄. Pieces of magnetite can be found scattered on or near the surface of the earth, and occasionally, one will be magnetized. These naturally occurring magnets are called lodestones. "We still are not certain as to their origin, but most scientists believe that lodestone is magnetite that has been hit by lightning," according to the University of Arizona.

People soon learned that they could magnetize an iron needle by stroking it with a lodestone, causing a majority of the unpaired electrons in the needle to line up in one direction. According to NASA, around A.D. 1000, the Chinese discovered that a magnet floating in a bowl of water always lined up in the north-south direction. The magnetic compass thus became a tremendous aid to navigation, particularly during the day and at night when the stars were hidden by clouds.

Other metals besides iron have been found to have ferromagnetic properties. These include nickel, cobalt, and some rare earth metals such as samarium or neodymium which are used to make super-strong permanent magnets.

Magnetism takes many other forms, but except for ferromagnetism, they are usually too weak to be observed except by sensitive laboratory instruments or at very low temperatures. Diamagnetism was first discovered in 1778 by Anton Brugnams, who was using permanent magnets in his search for materials containing iron. According to Gerald Küstler, a widely published independent German researcher and inventor, in his paper, "Diamagnetic Levitation - Historical Milestones," published in the Romanian Journal of Technical Sciences, Brugnams observed, "Only the dark and almost violet-colored bismuth displayed a particular phenomenon in the study; for when I laid a piece of it upon a round sheet of paper floating atop water, it was repelled by both poles of the magnet."

Bismuth has been determined to have the strongest diamagnetism of all elements, but as Michael Faraday discovered in 1845, it is a property of all matter to be repelled by a magnetic field.

Diamagnetism is caused by the orbital motion of electrons creating tiny current loops, which produce weak magnetic fields, according to HyperPhysics. When an external magnetic field is applied to a material, these current loops tend to align in such a way as to oppose the applied field. This causes all materials to be repelled by a permanent magnet; however, the resulting force is usually too weak to be noticeable. There are, however, some notable exceptions.

Pyrolytic carbon, a substance similar to graphite, shows even stronger diamagnetism than bismuth, albeit only along one axis, and can actually be levitated above a super-strong rare earth magnet. Certain superconducting materials show even stronger diamagnetism below their critical temperature and so rare-earth magnets can be levitated above them. (In theory, because of their mutual repulsion, one can be levitated above the other.)

Paramagnetism occurs when a material becomes magnetic temporarily when placed in a magnetic field and reverts to its nonmagnetic state as soon as the external field is removed. When a magnetic field is applied, some of the unpaired electron spins align themselves with the field and overwhelm the opposite force produced by diamagnetism. However, the effect is only noticeable at very low temperatures, according to Daniel Marsh, a professor of physics at Missouri Southern State University.

Other, more complex, forms include antiferromagnetism, in which the magnetic fields of atoms or molecules align next to each other; and spin glass behavior, which involve both ferromagnetic and antiferromagnetic interactions. Additionally, ferrimagnetism can be thought of as a combination of ferromagnetism and antiferromagnetism due to many similarities shared among them, but it still has its own uniqueness, according to the University of California, Davis.

When a wire is moved in a magnetic field, the field induces a current in the wire. Conversely, a magnetic field is produced by an electric charge in motion. This is in accordance with Faraday's Law of Induction, which is the basis for electromagnets, electric motors and generators. A charge moving in a straight line, as through a straight wire, generates a magnetic field that spirals around the wire. When that wire is formed into a loop, the field becomes a doughnut shape, or a torus. According to the Magnetic Recording Handbook (Springer, 1998) by Marvin Cameras, this magnetic field can be greatly enhanced by placing a ferromagnetic metal core inside the coil.

In some applications, direct current is used to produce a constant field in one direction that can be switched on and off with the current. This field can then deflect a movable iron lever causing an audible click. This is the basis for the telegraph, invented in the 1830s by Samuel F. B. Morse, which allowed for long-distance communication over wires using a binary code based on long- and short-duration pulses. The pulses were sent by skilled operators who would quickly turn the current on and off using a spring-loaded momentary-contact switch, or key. Another operator on the receiving end would then translate the audible clicks back into letters and words.

A coil around a magnet can also be made to move in a pattern of varying frequency and amplitude to induce a current in a coil. This is the basis for a number of devices, most notably, the microphone. Sound causes a diaphragm to move in an out with the varying pressure waves. If the diaphragm is connected to a movable magnetic coil around a magnetic core, it will produce a varying current that is analogous to the incident sound waves. This electrical signal can then be amplified, recorded or transmitted as desired. Tiny super-strong rare-earth magnets are now being used to make miniaturized microphones for cell phones, Marsh told Live Science.

When this modulated electrical signal is applied to a coil, it produces an oscillating magnetic field, which causes the coil to move in and out over a magnetic core in that same pattern. The coil is then attached to a movable speaker cone so it can reproduce audible sound waves in the air. The first practical application for the microphone and speaker was the telephone, patented by Alexander Graham Bell in 1876. Although this technology has been improved and refined, it is still the basis for recording and reproducing sound.

The applications of electromagnets are nearly countless. Faraday's Law of Induction forms the basis for many aspects of our modern society including not only electric motors and generators, but electromagnets of all sizes. The same principle used by a giant crane to lift junk cars at a scrap yard is also used to align microscopic magnetic particles on a computer hard disk drive to store binary data, and new applications are being developed every day.

Staff Writer Tanya Lewis contributed to this report.

Additional resources

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What Is Magnetism? | Magnetic Fields & Magnetic Force

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Magnetism is one aspect of the combined electromagnetic force. It refers to physical phenomena arising from the force caused by magnets, objects that produce fields that attract or repel other objects. A magnetic field exerts a force on particles in the field due to the Lorentz force, according to Georgia State University's HyperPhysics website.

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Welcome to Britannica School , a safe, up-to-date, and age-appropriate information resource for Elementary, Middle, and High School.

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Magnet Basics

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This liquid rocket fuel becomes magnetised when near a magnetic field. So it dances and morphs when magnets are moved around it.

It is called ferrofluid and it was invented by NASA's Steve Papell to be a rocket fuel that could work in zero gravity due to its magnetic qualities.

Magnet Expert Ltd recorded the experiment using a selection of strong neodymium magnets which can be bought on their website.
Produced by Leon Siciliano

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Watching magnets morph liquid rocket fuel is hypnotically beautiful

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This liquid rocket fuel becomes magnetised when near a magnetic field. So it dances and morphs when magnets are moved around it. It is called ferrofluid and it was invented by NASA's Steve Papell to be a rocket fuel that could work in zero gravity due to its magnetic qualities.