Observation of Giant Zero-Field Cooled Spontaneous Exchange Bias Effect in La2FeCoO6 Double Perovskite Ceramic

Abstract

The La₂FeCoO₆ ceramic was synthesized via the sol–gel route, and their temperature-dependent exchange bias (EB) effects have been analyzed at different magnetic fields. XRD investigation reveals that at a lower temperature, the monoclinic structure with the P2₁/n space group was maintained, whereas, from room temperature to 450 K, the rhombohedral structure with the R3c space group was noticed. The tolerance factor suggested the presence of distortion, and the XPS analysis of Fe and Co confirms the defect sites in La₂FeCoO₆. Hence, the variety of magnetic phases formed during the FC and ZFC processes resulted in unidirectional anisotropy. Negative field cooling magnetization was observed in M-T measurements, and ferromagnetic clusters were detected at room temperature M-H measurements. Negative EB fields and upward shifts in hysteresis were observed at low temperatures. The hysteresis and EB fields changed below the Neel transition, with a transition from positive to negative EB observed with increasing magnetic field and temperature. The observed EB was attributed to the pinning effect of surface spins in interfacial frozen glassy states at the interface of large ferrimagnetic grains.