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)/BiFeO
₃
(t
_BFO
)/Ni
₈₀
Fe
₂₀
(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.