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Characteristics of magnetic materials

2021-01-15 09:24

‍Magnetic data is a kind of old and young fundamental functional data. As early as the spring and Autumn period and the Warring States period, Sinan (picture) was created by our ancestors, and nearly all kinds of mechanical and electrical equipment supporting modern industry. Magnetic materials run through the history of human culture.

So far, a variety of magnetic data, such as permanent magnetic data, soft magnetic data and magnetic storage data, not only play an irreplaceable key role in aerospace, nuclear energy industry and other military and civil high-tech fields, but also are widely used in medical equipment, transportation, information storage and transmission and other daily life planning, grasp the general trend and play a good vanguard.

The data that can respond to the magnetic field in a certain way is called magnetic data. According to the magnetic strength of matter in external magnetic field, it can be divided into diamagnetic matter, paramagnetic matter, ferromagnetic matter, antiferromagnetic matter and ferromagnetic matter. Most of the data are diamagnetic or paramagnetic, and their responses to the external magnetic field are weak. Ferromagnetic material and sub ferromagnetic material are strong magnetic material. Generally speaking, magnetic material refers to strong magnetic material. As for magnetic data, magnetization curve and hysteresis loop are characteristic curves reflecting fundamental magnetic properties. Ferromagnetic data are generally Fe, Co, Ni elements and their alloys, rare earth elements and their alloys, and some Mn compounds. According to the difficulty level of magnetization, magnetic data can be divided into soft magnetic data and hard magnetic data.

The data with ferromagnetic properties have the following characteristics:

① Even if there is no external magnetic field, there is still permanent magnetic moment in each small area (domain) inside the data. However, when there is no external magnetic field, the direction of magnetic moment of each domain is arbitrarily scattered, and its vector sum is zero, so the data as a whole is not magnetic.

② Easy to magnetize. This is because the magnetic moment direction of each domain tries to turn to the magnetic field direction under the action of the external magnetic field, so a large magnetic induction intensity B can be obtained. According to the formula B = μ RB0 (B0 is the magnetic induction intensity in vacuum), the relative permeability μ r of magnetic data is very large. In practice, the μ r of magnetic data is 10-10, but the μ r of non-magnetic data is about 1.

③ There is a phenomenon of magnetic saturation, that is, B increases with the increase of H, but when BS increases to a certain value, it does not increase with H. BS is the saturation magnetic induction of the magnetic data. The reason for the saturation phenomenon is that when h reaches a certain value, the magnetic moments of all domains turn to the direction of magnetic field. Because of this reason, B and H do not have a linear relationship, so the permeability is not a constant, but is related to the strength of the magnetic field.

④ There is hysteresis. That is to say, the change of magnetic induction lags behind the change of magnetic field‍