Depending on the magnetic properties, substances are diamagnetics, paramagnets and ferromagnets. And it is the ferromagnetic material that has special properties that differ from the rest.
What is this material and what properties does it have
A ferromagnetic material (or ferromagnet) is a substance in a solid crystalline or amorphous state that 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.
Ferromagnet Groups
In total, there are two groups of ferromagnetic material:
- Soft magnetic band. Ferromagnets of this group have small magnetic field strengths, but have excellent magnetic permeability (less than 8.0 × 10 -4 GN / m) and low hysteresis losses. Soft magnetic materials include: permalloys (alloys with the addition of nickel and iron), oxide ferromagnets (ferrites), and magnetodielectrics.
- Magnetically hard (or magnetically hard group). The characteristics of ferromagnetic materials in this group are higher than in the previous one. Solid-magnetic substances have both high magnetic field strengths and good magnetic permeability. They are the basic materials for the production of magnets and devices where coercive force is used and excellent magnetic susceptibility is required. Almost all carbon and some alloy steels (cobalt, tungsten and chromium) belong to the magnetically hard group.
Soft magnetic materials
As mentioned earlier, the soft magnetic group includes:
- Permalloys, which consist only of alloys of iron and nickel. Sometimes chromium and molybdenum are added to permalloys to increase permeability. Properly made permalloys are characterized by high magnetic permeability and coercive force.
- Ferrites - a ferromagnetic material consisting of iron and zinc oxides. Often, manganese or nickel oxides are added to iron and zinc to reduce resistance. Therefore, ferrites are often used as semiconductors at high frequency currents.
- Magnetodielectrics are a ground mixture of iron, magnetite or permalloy powder wrapped in a dielectric film. Like ferrites, magnetodielectrics are used as semiconductors in a wide variety of devices: amplifiers, receivers, transmitters, etc.
Hard magnetic materials
The following materials belong to the hard magnetic group:
- Carbon steels consisting of an alloy of iron and carbon. Depending on the amount of carbon, there are: low carbon (less than 0.25% carbon), medium carbon (0.25 to 0.6% carbon) and high carbon steels (up to 2% carbon). In addition to iron and carbon, the composition of the alloy may also include silicon, magnesium and manganese. But the most high-quality and suitable ferromagnetic materials are those carbon steels that have the least amount of impurities.
- Alloys based on rare-earth elements, for example, samarium-cobalt alloys (SmCo5 or Sm2Co17 compounds). They have high magnetic permeability with a residual induction of 0.9 T. In this case, the magnetic field in ferromagnets of this type is also 0.9 T.
- Other alloys. These include: tungsten, magnesium, platinum and cobalt alloys.
Difference of ferromagnetic material from other substances with magnetic properties
At the beginning of the article, it was said that ferromagnets have special properties that differ significantly from other materials, and here are some evidence:
- Unlike diamagnets and paramagnets, which derive their properties from individual atoms and molecules of a substance, the properties of ferromagnetic materials depend on the crystal structure.
- Ferromagnetic materials, unlike, for example, paramagnets, have large values of magnetic permeability.
- In addition to permeability, ferromagnets differ from paramagnetic materials also in that they have a dependent relationship between magnetization and the strength of the magnetizing field, which has the scientific name - magnetic hysteresis. Many ferromagnetic materials, such as cobalt and nickel, as well as alloys based on them, are susceptible to this phenomenon. By the way, it is magnetic hysteresis that allows magnets to maintain their magnetization state for a long time.
- Some ferromagnetic materials also have the ability to change their shape and size during magnetization. This phenomenon is called magnetostriction and depends not only on the type of ferromagnet, but also on other equally important factors, for example, field strengths 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, more 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 external phenomena and is almost invisible to the naked eye.
Scope 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;
- Winchesters for laptops and PCs;
- loudspeakers and some types of telephones;
- sound recording devices.
In the past, some soft magnetic materials were also used in radio engineering to create magnetic tapes and films.