Dependence of Ferromagnetic Anisotropy on the Field Strength

In evaluating the anisotropy constants of ferromagnetic materials a common method is to measure the torque exerted on a specimen of circular section by a uniform magnetic field, to determine the maximum torque by extrapolation to infinite field strength, and to multiply this by an appropriate number. The law of approach of the torque, $T_H$, to its limiting value, $T_{\infty }$, is now found to be $T_H=T_{\infty }(1-\frac{H_0}{H_a})$ for a number of disks and ellipsoids of single crystals of iron-silicon alloys containing up to 7.4 percent silicon, and for polycrystalline disks of iron and of silicon steel. Here $H_a$ is the strength of the applied field uncorrected for demagnetizing field and $H_0$ is a constant which depends mostly upon the dimension-ratio of the disk. This law is discussed in relation to a similar law proposed by Schlechtweg, and to the familiar law of approach of magnetization to saturation. It is concluded that for disks the approach to saturation of the torque peaks is connected with the lack of magnetic saturation at their edges.