Resonance Measurements on Nickel-Cobalt Ferrites as a Function of Temperature and on Nickel Ferrite-Aluminates

The variation of line width (Delta H) and effective g factor (g_eff) with cobalt content and with temperature is studied in a series of ferrites of composition Ni_{1- alpha}Co_alphaMn_0.02Fe_1.9O_4+-. Here alpha lies between 0 and 0.09; temperatures range from 20° to 340° C. A minimum in Delta H is observed at alpha=0.027; g_eff decreases with increasing alpha. The temperature dependence of each is qualitatively that which would be expected on the basis of the temperature dependence of the anistrophy of the mixed ferrite. Above room temperature Delta H and g_eff increase or decrease, depending on the cobalt content. It is also shown that the shape of the resonance line is determined by the sign of the anisotropy constant. For negative K₁ the line is steeper on the low-field side of resonance--for positive K₁ it is steeper on the high-field side. Resonance data are presented on several nickel-cobalt ferrite-aluminates, of composition Ni_{1_alpha}Co_alphaMn_0.02Fe_2-tAl_tO_4+-, with alpha varying from 0 to 0.025 for t=0.3, 0.4, 0.5, and 0.6. The reduction of Delta H and g_eff expected from anisotropy considerations is observed.