Magnetic Anisotropy in Ferrimagnetie Crystals

Absolute values of K1, the first-order anisotropy constant, have been determined at different temperatures from torque measurements on single crystals of the following compositions: MnxFe3−xO4, where 0.7 ≤ x ≤ 1.0; Cox Mn1−xFe2O4, where 0 ≤ x ≤ 0.25; Co0.04Mnx−0.04Fe3−xO4, where 0.70 ≤ x ≤ 0.91; GaxFe3−xO4, where 0 ≤ x ≤ 0.8; Sm3Fe5O12 Gd3Fe5O12.The magnetocrystalline anisotropy of manganese ferrous ferrite was found to vary considerably with the concentration of ferrous ions (Fe2+), some compositions even possessing a positive value of K1 at room temperature, as previously found by Penoyer (1959). In these cases, K1 becomes negative at low temperatures in contrast with the behavior of cobalt-substituted crystals which are found to have rapidly increasing positive values of K1 as the temperature is reduced. The anisotropy contribution of cobalt ions (Co2+) substituted in manganese ferrous ferrite varies with crystals of different compositions.The experimental values of K1 are compared wherever possible wi...