Magnetic induction B and magnetic polarization J

Practice and theory have proved that when a ferromagnetic or ferrimagnetic substance is magnetized in a magnetic field, in addition to the magnetic field in the substance, because the magnetic moments of the atoms of the ferromagnetic substance turn to the direction of the external magnetic field, it generates an additional magnetic field M inside the substance . The sum of the external magnetic field and the additional magnetic field at this time is called the magnetic induction of the magnet.

Magnetic induction B and magnetic polarization J

Magnetic induction B and magnetic polarization J

Magnetic induction B

The magnetic induction intensity B is the total magnetic field “felt” by the magnet, which is the sum of the applied magnetic field H and the induced magnetic field M at this time. In a vacuum environment, the magnetic induction intensity is proportional to the external magnetic field, that is, B=μ0H, where μ0 is the vacuum permeability, and μ0=4π×10-7H/m (Henry/meter).

The magnetic induction inside the magnet is B=μ0(H+M). The unit of B is Tesla T, and the unit in the Gauss unit system is Gauss Gs (1T=10KGs).

Magnetic polarization J

Magnetic induction B=μ0(H+M)=μ0H+μ0M, we call μ0M the magnetic polarization of the material, that is, J=μ0M, and its unit is T (Tesla). The magnetic polarization J is interpreted as the magnetic dipole moment per unit volume of the magnetic medium in a physical sense, also known as the intrinsic magnetic induction. The symbol is Bi or J.

In soft magnetic materials, the value of the magnetic field strength is usually not more than 1000A/m, μ0 is 4×10-7H/m, and J=B-μ0H, so the difference between the magnetic induction B and the magnetic polarization J is very small; But in hard magnetic materials, this difference is very significant, so B-H curve and J-H curve are usually given.

The second quadrant in the above figure is the demagnetization curve of the magnet we often see. Next week, we will further introduce the magnetic parameters of magnetic materials implied in the B-H curve and J-H curve in the magnetic column every Monday.

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