Exchange bias induced by the spin glass-like phase in multifunctional ferrimagnetic CoFe₂O₄ thin films

Exchange bias is a characteristic with wide technological utility; however, the underlying mechanism of planar exchange bias in thin films remains elusive. Herein, a series of ferrimagnetic CoFe₂O₄ (CFO) thin films with different thicknesses are deposited by DC magnetron sputtering. A giant exchange bias field of approximately 11.1 kOe, accompanied by a high coercivity of approximately 25.1 kOe, is observed at 5 K. The evident branching behavior in the magnetization curves and the magnetic relaxation characteristics both indicate a glassy transition in the system. Importantly, we observe a correlation between the freezing temperature of the spin glass-like phase and the temperature at which the exchange bias disappears. This suggests that the exchange bias in the films is caused by unidirectional anisotropy, which arises from the coupling between the FIM and spin glass-like phases. In addition, CFO thin films show a rapid photoresponse in the visible light range, making them multifunctional materials with self-powered properties. These findings offer novel perspectives and important insights into the intrinsic mechanisms of exchange bias in ferrimagnetic materials, highlighting the potential of CFO thin films in spintronic-optoelectronic integrated applications.