What is Ferromagnetism

What is ferromagnetism

If the atoms have magnetic moments in the material, they can be called magnetic materials. Iron, cobalt, nickel and manganese have magnetic moments with their alloy atoms, which are common magnetic materials. Gold, silver, copper, aluminum and other atoms have no magnetic moment and are non-magnetic materials.

But magnetism includes ferromagnetism, antiferromagnetism, spin glass and so on.

In ferromagnetic materials (each arrow in the picture represents the magnetic moment of an atom).

The adjacent magnetic moments are arranged parallel to each other, showing ferromagnetism as a whole.


In antiferromagnetic materials, because the adjacent magnetic moments are antiparallel, the magnetic moments cancel each other, and the whole does not show magnetism.


There are several kinds of magnetic materials.

2. The arrangement of magnetic moments in ferromagnetic materials.

Only ferromagnetic materials are mentioned below.

For a large piece of magnet, its spontaneous magnetic moments will not be arranged in one direction.


Thus, although the material is ferromagnetic, it is divided into many magnetic domains that cancel each other out and there is no overall magnetism. Technically, this is the complete “demagnetization state” of magnets.

If the magnet is placed in a large magnetic field, all the magnetic moments can be pulled in the same direction, “saturated magnetization”.

For a hard magnetic material, the magnetic moment is still single domain along one direction after the magnetic field is removed.


For example, the diagram above shows that the magnet is N pole on the right and S pole on the left.

Permanent magnets exposed to everyday life are made of hard magnetic materials. The so-called permanent magnetism is the removal of magnetic field and magnetism.

For soft magnetic materials, the magnetic field is removed and returned to the “demagnetized state”. The magnetism disappears and there is no magnetic pole. Soft magnetic is usually used in the core of the electromagnet.

3. Effect of shape on magnet poles

First of all, the shape of permanent magnets in hard magnetic materials can be neglected. The distribution of magnetic poles is related to the material itself and the history of magnetization. That is to say, when saturation magnetization is initially performed in a large magnetic field, the N pole is in that direction in which the external magnetic field is applied. There is no difference between the ring type or the ball type.

So, if it’s a soft magnetic material, like Permalloy, then the distribution of magnetic moments depends on shape, size, and so on, which is more fun.

First, for a disk, there may be magnetic vortices. The magnetic moments in the disk are arranged in a rotating arrangement, but the center is vertical.


Turn into a ring, that is, onion.



In these cases, it is difficult to define the traditional poles.

As for the magnetic ball, a magnetic moment distribution is shown below.


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What are the Types of Magnets?

There are many kinds of magnets, generally divided into permanent magnets and soft magnets.

Permanent magnet is divided into two categories:

The first category is: metal alloy magnets include NdFeB, SmCo and AlNiCo magnets.

The second category is ferrite permanent magnet.


1. Neodymium-iron-boron magnet: It is the most commercially available magnet, known as the magnet king, with extremely high magnetic properties, its maximum magnetic energy product is more than 10 times higher than that of ferrite. Its mechanical properties are quite good. The working temperature can reach up to 200 degrees Celsius. Moreover, its texture is hard, its performance is stable, and its cost performance is very good, so its application is extremely extensive. But because of its strong chemical activity, the surface layer must be treated.

2. Ferrite magnet: its main raw materials include BaFe12O19 and SrFe12O19. It is a brittle material with hard texture. Ferrite magnet has been widely used because of its good temperature resistance, low price and moderate performance.

magnets assembly

3. Aluminum nickel cobalt magnet: an alloy consisting of aluminum, nickel, cobalt, iron and other trace metals. The casting process can be made into different sizes and shapes, with good workability. The cast aluminum nickel cobalt permanent magnet has the lowest reversible temperature coefficient, and the working temperature can reach up to 600 degrees Celsius. Al Ni Co permanent magnet products are widely used in various instruments and other applications.

4. Samarium cobalt (SmCo) is divided into SmCo5 and Sm2Co17 according to their components. Because of the high price of materials, their development is limited. SmCo, as a rare earth permanent magnet, not only has a high magnetic energy product, reliable coercivity, and good temperature characteristics. Compared with NdFeB magnets, samarium cobalt magnet is more suitable for working in a high-temperature environment.

Speaker Magnet And Its Effect on Sound Quality

Types of magnets:

1. Alloy magnet
Aluminum nickel cobalt magnet, also known as speaker magnet. It was generally made of internal magnetic horn. It has small power, narrow frequency range, it is hard and brittle.

Alloy magnet

2. Iron oxide magnet
It sintered from magnetic material powder and iron powder at about 1200 degrees centigrade. It was generally made of external magnetic horn, it is low in price, high in quality. Its disadvantages are large volume, small power, and narrow frequency range.

Iron oxide magnet

3. NdFeB magnet
Its performance is much better than that of iron oxide magnets. The magnetic strength of the same volume is 10 times higher than that of general iron oxide. Its characteristics: the same magnetic flux under its small size, large power, wide frequency range, HiFi headphones are basically using this kind of magnet.

NdFeB magnet

The influence of magnets on the sound quality of loudspeakers:
1) The better the magnet material is, the greater the magnetic flux density B is, and the stronger the force acting on the sound film is.

2) The larger the magnetic flux density B is, the greater the power is, and the higher the SPL sound pressure level (sensitivity) is.

Headphone Sensitivity: When pointing to the earphone and inputting 1 MW, 1 kHz sine wave, the sound pressure level (sound pressure unit is dB, the greater the sound pressure, the greater the volume), so the higher the general sensitivity is, the smaller the impedance is, the easier the earphone sounds is.

3) The larger the density of magnetic flux B is, the lower the total quality factor Q of the loudspeaker is.

Q (quality) is a set of parameters of the damping factor. In TS parameters, Q values are divided into Qms, Qes, and Qts. Qms is the damping of the mechanical system, which reflects the absorption and consumption of energy in the motion of the horn components. Qes is the damping of the power system, mainly reflected in the voice coil DC resistance of the power consumption; Qts is the total damping, and the above two are related to Qts = Qms * Qes /(Qms Qes).

4) The greater the flux density B is, the better the transient is.

Transients can be understood as “fast response” to signals, and Qms is relatively high. The earphone with the good transient response should respond immediately when the signal comes, and the signal stops abruptly when it stops. In particular, it is most obvious that the transition from music to Orchestra in the orchestra of drum music and larger scenes is most obvious.


The quality of the magnet is one of the important factors affecting the quality of the sound.

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The Strongest Permanent Magnet-Neodymium Magnets

At room temperature, the neodymium magnet is the most powerful permanent magnet.

But this is only at room temperature. Early Neo magnets had an annoying flaw: they were sensitive to temperature, and when the temperature rose, the magnetism dropped dramatically, and when it was above 100 degrees Celsius, it was completely demagnetized. But now an improvement has been found by adding a small amount of dysprosium, another rare earth metal, which is less sensitive to temperature changes.

neo magnets

At the same time, a technological revolution driven by permanent magnets opened the curtain. Anywhere you want to produce the strongest magnetic field with the least amount of material, Neo permanent magnets are preferred: car engines, spindle motors on CD and DVD readers, electric signals converted into sound diaphragms in headphones and speakers, and super magnetic fields needed in medical magnetic resonance technology… By 2010, even though cheaper ferrites still dominated the market, neodymium permanent magnets were worth more than a dozen or even hundreds of times more than ferrites in terms of volume.

However, when Neo permanent magnets were developed, the demand for rare earth metals surged. Rare earth metals aren’t really rare on the planet — they are a few parts per million in the earth’s crust — they’re “rare” because they’re hard to find.

Search for new permanent magnet materials

Each computer needs only 50 grams of Neo permanent magnet. It doesn’t seem like much, but given the number of computers around the world, it’s almost an astronomical number. Now, with the rise of green energy technology, the consumption of computers has become a great mystery. Turbine motors in wind farms, as well as electric cars and bicycles, require lightweight and powerful permanent magnets, and only Neo magnets currently meet the requirements. Each electric vehicle consumes 2 kilograms of Neo permanent magnets. The power of megawatt wind turbines will consume 2/3 tons of Neo permanent magnets. Therefore, it is imminent to develop new and stronger permanent magnets. It is better to reduce the number of rare earth metals. The ideal situation is to stop using rare earth metals.

Neo magnet

The United States has invested huge sums of money in finding new permanent magnets. At present, scientists are trying to improve the performance of Fe Ni alloy permanent magnets. Usually, when two magnetic metals, iron and nickel, are fused together, they form disordered structures in which it is difficult to align electrons in the same direction. One exception, however, is that iron and nickel atoms are arranged in regular layers in a mineral called cubic nickel rubble. Once a magnetic field is applied, the electron spins tend to move in the same direction.

But this mineral is very difficult to form under natural conditions, especially on the earth. In fact, the only orthoclase sample in the world today comes from a meteorite that took at least billions of years to form. One billion years is certainly too long for us. The goal of scientists is to synthesize it in the laboratory and do what nature needs to do in billions of years.

Another ongoing attempt that seems to be completely different is to use carbon as a permanent magnet. It is well known that graphite and diamond are nonmagnetic, and the incorporation of carbon into pure iron also makes it lose its magnetism. But making compounds of carbon and other elements into nanoparticles is another matter. Scientists found that the material showed strong magnetism. For commercial secrecy, what the material is and how to make it is not convenient for scientists to disclose. But they say the permanent magnet will one day beat neodymium at both performance and price.

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How are Permanent Magnets Made?

Today, mobile phones, headsets, and other devices are made so small that they can’t be separated from high-performance permanent magnets. So how are these magnets made? Can we find more powerful magnets?
“Magnet”, the scientific term is called a permanent magnet, which is different from the electrified magnet. It’s the core of many modern technologies. Speakers in compact devices such as cell phones and headphones require permanent magnets to convert current signals into sound signals. With super permanent magnets, they can now be so compact. In addition, electric vehicles, turbines, computers, satellites, and so on, all require permanent magnets to convert electrical and mechanical energy into each other.

permanent magnets
So how are permanent magnets made?
It is not difficult to make a permanent magnet. Electromagnetism tells us that the movement of electric charge produces the magnetic field, which can make the charge move. So permanent magnets play a central role in electric motors, generators, and transformers. There, they store energy or transform mechanical energy and electrical energy into one another. These devices are still playing a great role in our daily life.

magnetic field
Rare earth permanent magnet material debut
It is so simple to make a permanent magnet, but it is not easy to make a good permanent magnet. There are many materials used to make permanent magnets. We can make a long list. The most used is ferrite, because it is relatively cheap, and its corrosion resistance is also unmatched. But it has a fatal flaw: magnetism is not strong enough. In order to produce a strong magnetic field, you need a lot of amazing ferrites. So devices containing ferrite magnets are generally large and bulky.
It is certainly not a problem for large mechanical devices, but in this age of microelectronics, we need smaller things, which require more magnetic permanent magnets. But how do you get it? In a solid material, the number of electrons is too large for theoretical calculations, so it is difficult for theorists to give guidance. In this case, the search for better permanent magnets depends largely on metallurgists’experiments: mixing promising elements into an external magnetic field to see what happens.
In this way, the magnetism of the AlCoNi magnet developed in the 1930s is almost double that of the best ferrite magnets. But in this area, a series of breakthroughs occurred after the 1970s, an excellent material for making permanent magnets, were discovered.
Rare earth elements are also known as lanthanides in the periodic table, with atomic numbers ranging from 57 to 71. Important rare earth elements include rubidium (Nd) of atomic number 60, samarium (Sm) of 62 and dysprosium (Dy) of 66. One of the characteristics of these elements is that there are so many electrons in their atoms that spin in the same direction. In the 1970s, cobalt and samarium were mixed in proportion to form permanent magnets, which were found to be twice as magnetic as aluminum cobalt nickel permanent magnets.

The most dazzling star in permanent magnets
Nevertheless, an incomparable star in permanent magnets is the NdFeB permanent magnet (Neo magnet). In the 1990s, this permanent magnet, at equal distances, was thousands of times stronger than the magnetic field produced by the Earth’s liquid iron core. You know, the average distance between the earth’s surface and the liquid iron core that produces a magnetic field on the earth is 2900 kilometers, which means that the magnetism of the Neo permanent magnet is thousands of times stronger than that of the earth’s magnetic field.
At room temperature, Neo magnet is the most powerful permanent magnet.