Anomalous magnetic properties of an iron film system deposited on fracture surfaces of \alpha-Al₂O₃ ceramics

An iron film percolation system is fabricated by vapour-phase deposition on fracture surfaces of \alpha-Al₂O₃ ceramics. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurement reveals that the magnetic phase of the film samples evolve from a high-temperature ferromagnetic state to a low-temperature spin-glass-like state, which is also demonstrated by the temperature-dependent ac susceptibility of the iron films. The temperature dependence of the exchange bias field H_\rm e of the iron film exhibits a minimum peak around the temperature T=5 K, which is independent of the magnitude of the cooling field H_\rm cf. However, for T > 10 K, (1) H_\rm e is always negative when H_\rm cf=2 kOe and (2) for H_\rm cf = 20 kOe (1Oe\approx80 A/m), H_\rm e changes from negative to positive values as T increases. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase.