Effect of Important Factors on Temperature Variation of Coercivity in Sr-La-Co High-Performance Sintered Ferrite Magnets

The authors varied the composition of Sr_1-xLa_xFe_12-xCo_xO₁₉ sintered ferrite magnets (x=0-0.4) for analyzing the effects of various factors on the temperature variation of coercivity (H_cJ) in the temperature range between 173 and 423 K, where x is the substituted amount. The effects of the crystal grain size (C_t), the mechanism of magnetization reversal (R_h), the degree of crystal grain orientation (OD), and the anisotropy field (H_A) on the temperature variation of H_cJ were also examined. It was confirmed that the equation H_cJ=C_t(0.4/R_h) OD (H_A-H_d-H_in) was applicable for expressing the measured H_cJ in a wide temperature range between 173 and 423 K for all the magnets, where H_d and H_in are the demagnetizing field of shape anisotropy and the interaction field between crystal grains, respectively. Above all, the factors of C_t, R_h, and H_A had significant effects on the temperature variation of H_cJ for all the magnets.