Exchange bias in BiFeO3/Ni81Fe19 magnetic films and its thermal stability

This paper deals with the exchange bias and its thermal stability in magnetic BiFeO3/Ni81Fe19 bilayer sputtered under an electromagnetic field. The results show that the BiFeO3/Ni18Fe19 bilayer presents an in-plane uniaxial magnetic anisotropy and a significant exchange bias effect, however the exchange bias field H in the BiFeO3/Ni18Fe19 bilayer does not show a visible training effect. The forward and recoil loop shifts towards positive fields, while holding the film in a negative saturation field. H-ex decreases monotonously with the increase in the holding time (t(sat)), whereas H is almost the same. With increasing temperature T-m, H-ex will not alter significantly, which means that H-ex is not sensitive to the temperature, showing a good thermal stability. However, H-c may reduce rapidly with the increase in temperature. We believe that the good thermal stability may result from the coupling between ferroelectric and antiferromagnetic moments in BiFeO3.