Depending on the magnetic properties, substances are diamagnets, paramagnets and ferromagnets. And it is the ferromagnetic material that has special properties that differ from the rest.
What kind of material is this and what properties does it have
A ferromagnetic material (or ferromagnet) is a substance that is in a solid crystalline or amorphous state, which is magnetized in the absence of any magnetic field only at a low critical temperature, i.e. at a temperature below the Curie point. The magnetic susceptibility of this material is positive and exceeds unity. Some ferromagnets may have spontaneous magnetization, the strength of which will depend on external factors. Among other things, such materials have excellent magnetic permeability and are capable of amplifying an external magnetic field by several hundred thousand times.
Groups of ferromagnets
There are two groups of ferromagnetic material in total:
- Magnetically soft group. Ferromagnets of this group have smallindicators of magnetic field strength, but have excellent magnetic permeability (less than 8.0×10-4 H/m) and low hysteresis losses. Soft magnetic materials include: permalloys (alloys with the addition of nickel and iron), oxide ferromagnets (ferrites), magnetodielectrics.
- Magnetically hard (or magnetically hard group). The characteristics of ferromagnetic materials of this group are higher than those of the previous one. Magnetic solids have both high magnetic field strengths and good magnetic permeability. They are the main materials for the production of magnets and devices where coercive force is used and excellent magnetic susceptibility is required. The magnetically hard group includes almost all carbon and some alloy steels (cob alt, tungsten and chromium).
Materials of magnetically soft group
As mentioned earlier, the soft magnetic group includes:
- Permalloys, which consist only of iron and nickel alloys. Chromium and molybdenum are sometimes added to permalloys to increase permeability. Properly made permalloys have high magnetic permeability and coercive force.
- Ferrites are a ferromagnetic material consisting of oxides of iron and zinc. Often manganese or nickel oxides are added to iron and zinc to reduce resistance. Therefore, ferrites are often used as semiconductors for high-frequency currents.
- Magnetodielectricsare a powdered mixture of iron, magnetite or permalloy powder wrapped in a dielectric film. Just like ferrites, magnetodielectrics are used as semiconductors in a wide variety of devices: amplifiers, receivers, transmitters, etc.
Materials of the hard magnetic group
The following materials belong to the hard magnetic group:
- Carbon steels made from an alloy of iron and carbon. Depending on the amount of carbon, there are: low-carbon (less than 0.25% carbon), medium-carbon (from 0.25 to 0.6% carbon) and high-carbon steels (up to 2% carbon). In addition to iron and carbon, silicon, magnesium and manganese can also be included in the composition of the alloy. But the highest quality and suitable ferromagnetic materials are those carbon steels that have the least amount of impurities.
- Alloys based on rare earth elements, such as samarium-cob alt alloys (SmCo5 or Sm2Co17 compounds). They have high magnetic permeability with a residual induction of 0.9 T. At the same time, the magnetic field in ferromagnets of this type is also 0.9 T.
- Other alloys. These include: tungsten, magnesium, platinum and cob alt alloys.
The difference between a ferromagnetic material and other substances with magnetic properties
At the beginning of the article, it was said that ferromagnets have special properties that differ significantlyfrom other materials, and here are some proofs:
- Unlike diamagnets and paramagnets, which derive their properties from individual atoms and molecules of matter, the properties of ferromagnetic materials depend on the crystal structure.
- Ferromagnetic materials, unlike, for example, paramagnets, have high values of magnetic permeability.
- In addition to permeability, ferromagnets differ from paramagnetic materials in that they have a dependent relationship between magnetization and magnetizing field strength, which has a scientific name - magnetic hysteresis. Many ferromagnetic materials, such as cob alt and nickel, as well as alloys based on them, are subject to a similar phenomenon. By the way, it is the magnetic hysteresis that allows magnets to maintain a state of magnetization for a long time.
- Some ferromagnetic materials also have the ability to change their shape and size when magnetized. This phenomenon is called magnetostriction and depends not only on the type of ferromagnet, but also on other equally important factors, for example, on the strength of the fields and the location of the crystallographic axes with respect to them.
- Another interesting feature of a ferromagnetic substance is the ability to lose its magnetic properties or, to put it simply, turn into a paramagnet. This effect can be achieved by heating the material above the so-called Curie point, while the transition to the paramagnetic state is not accompanied by any side effects and is practically invisible to the naked eye.eye.
Field of application of ferromagnets
As you can see, ferromagnetic material occupies a particularly important place in the modern world of technology. It is used in the manufacture of:
- permanent magnets;
- magnetic compasses;
- transformers and generators;
- electronic motors;
- electrical measuring instruments;
- receivers;
- transmitters;
- amplifiers and receivers;
- hard drives for laptops and PCs;
- loudspeakers and some types of telephones;
- recorders.
In the past, some soft magnetic materials were also used in radio engineering to create magnetic tapes and films.
