Spin-Glass Behavior in Co-Ferrite Amorphous Films

Amorphous Co-ferrite thin films not containing vitrifying elements were prepared by ion beam sputter deposition. Their magnetic properties were investigated by means of low-field dc magnetization and ac susceptibility measurements, which gave evidence of spin glass behavior. The temperature dependence of magnetization in a 50 Oe external field exhibited an irreversibility just below room temperature, which decreased with increasing field strength. A cusp in the ac susceptibility (80 Hz, 1 Oe) corresponding to the spin freezing temperature was observed at 284 K. Below this temperature, relaxation of the thermoremanent magnetization was observed. Besides this transition at 284 K, a sharp peak in the ac susceptibility at 86 K, suggestive of another transition, was observed. It is thought that spin glass ordering with a high freezing temperature is caused mainly by transition to an amorphous structure for strong superexchange interactions.