Characteristics of Iron in High Frequency Rotating Magnetic Fields

Characteristics of electrolytic iron in rotating magnetic fields of high frequency, 52,000 to 172,000 and of strength 0.7 to 5 gauss, have been determined by measurements on a disk, ${10}^{-3\mathrm{}}$ cm thick shellacked to a half inch cover glass. Equations are derived by which $H$ and $I$ can be computed from measurements of the impressed field, the fluxes through a coil with and without the disk in it, and the torque exerted on the disk by the rotating field. This field is produced by means of two Helmholtz coils with axes at right angles, each in series with a separate oscillating circuit, coupled to the main oscillating circuit. The results agree with previous work and show that (1) the susceptibility decreases with increasing frequency; (2) the hysteresis angle tends to increase with frequency and for a given frequency reaches a maximum for $I$ at about 500; (3) the hysteresis energy loss per cycle $E_h$ increases with frequency for constant magnetic intensity and decreases for constant field, the exponent $\alpha$ in the equation $E_h=A{H}^{\alpha }$ increasing from 2.9 to 3.37 as frequency is increased from 52 to 172 kilocycles.