Temperature dependence of the exchange bias properties in polycrystalline BiFeO3/Ni80Fe20

In this study, we report a temperature dependent analysis of the exchange bias properties in BFO/Py bilayers as a function of the BFO thickness. The temperature dependence of the exchange bias field (H_e) and the coercive field (H_c) are first presented. To understand exchange bias magnetization reversal and the magnetic anisotropies, we will then present an azimuthal study of H_e and H_c at 300 K and 77 K. Finally, results of a controlled field cooling protocol applied on all samples will be discussed to understand anisotropy energy distribution. The bilayers were grown by radio-frequency sputter deposition, with the following structure: Si/Pt(14 nm)/BiFeO₃(t_BFO)/Ni₈₀Fe₂₀(10 nm)/ Pt(10 nm), with t_BFO among 0 nm, 29 nm and 177 nm . To induce uniaxial anisotropy, a 300 Oe field H_dep was applied during the growth . The XRD analysis confirmed a single polycrystalline structure for the BFO layer.