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Orientation degree of strontium ferrite particles in a magnetic field at water-based wet-pressing stage was investigated from the viewpoint of calcining temperature and dispersant addition. In the case of no dispersant addition, the orientation degree was low especially at low calcining temperature (1150°C and 1200°C), at which the particle size was under micron. Increasing the calcining temperature, the orientation degree noticeably increased. On the other hand, we found that the orientation of the submicron sized particles was much improved by addition of calcium gluconate as a dispersant and then the orientation degree was almost independent of calcining temperature. It was predicted that calcium gluconate effectively deagglomerated submicron sized particles of strontium ferrite. Therefore addition of calcium gluconate enabled to produce high-performance ferrite magnets with both high coercivity and high remanence.

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.

Magnetic properties of anisotropic M-type Sr-ferrite containing La and Co (Sr1-xLaxCoxFe12-xO19) was investigated in detail. At a composition of x = 0.3, the magnetic properties for permanent magnets were much improved, with the highest values of Br = 4.45 kG, HcJ = 4.82 kOe, and (BH)max = 4.86 MGOe. The temperature dependence of the coercivity was also much improved, with ΔHcJ/HcJ/ΔT = 0.1 %/°C.

Lanthanum and zinc substitution in M-type hexaferrite was studied in detail in order to increase the saturation magnetization. For the composition Sr 0.7 La 0.3 Fe 11.7 Zn 0.3 O 19, the saturation magnetization was increased by more than 4% and the uniaxial anisotropy constant (K 1 ) was almost the same as that of non-substituted Ba-ferrite. Furthermore, high energy ferrite magnets having more than 40kJ/m 3 (5MGOe) were obtained for the first time by the new process for high orientation, high density and submicron-sized grains.