Magnetocrystalline Anisotropy of M-Type Sr-Ferrite Containing Lanthanum and Cobalt

The magnetic anisotropy constant K1 and anisotropy field HA of M-type Sr-ferrite containing La and Co (Sr0.7La0.3Fe11.7Co0.3O19) were investigated by the singular-point detection (SPD) method using a pulsed field and SQUID magnetometers, and also by torque measurements. The value of HA=22.2 kOe was obtained by the SPD method at 298 K. The K1 value was 4.2 × 106 erg/cm3 at 298 K, which was determined by extrapolation to the high field of the coefficient of the sin(2 φ) term calculated by Fourier analysis of unsaturated torque curves. This value was 15% larger than that of conventional Sr-ferrite (SrFe12O19) in the temperature range from 77 to 373 K.