Observation of reversed hysteresis loops and negative coercivity in CoFeAlO magnetic thin films

The magnetic and magneto-optical properties of CoFeAlO thin films fabricated by the RF magnetron reactive sputtering technique have been studied via vibrating sample magnetometer and the magneto-optical Kerr effect. It is found that, along the hard magnetization direction, the magnetic hysteresis loop is reversed and the coercive force is negative. This phenomenon can qualitatively be interpreted within the framework of the proposed two-layers model. It was also found that when as-deposited CoFeAlO thin films were annealed in vacuum (2×10−7 Torr) at a temperature of 180 °C for 2 h, the negative coercivity disappeared. The relationship between the magnetic and microstructural behaviors of the thin films is discussed.