Eur. Phys. J. B (2013) 86: 121
https://doi.org/10.1140/epjb/e2013-31003-y

Regular Article

Temperature dependent exchange bias effect in polycrystalline BiFeO₃/FM (FM  =  NiFe, Co) bilayers

¹ National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, P.R. China
² Department of Physics, Southeast University, Nanjing 211189, P.R. China
³ Department of Physics, Tongji University, Shanghai 200092, P.R. China

^a e-mail: xuqingyu@seu.edu.cn
^b e-mail: jdu@nju.edu.cn

Received: 3 November 2012
Received in final form: 23 January 2013
Published online: 27 March 2013

Abstract

Extensive studies on the temperature (T) dependent exchange bias effect were carried out in polycrystalline BiFeO₃(BFO)/NiFe and BFO/Co bilayers. In contrast to single-crystalline BFO/ferromagnet (FM) bilayers, sharp increase of the exchange bias field (H_E) below 50 K were clearly observed in both of these two bilayers. However, when T is higher than 50 K, H_E increases with T and decreases further when T is larger than 230 K (for BFO/NiFe) or 200 K (for BFO/Co), which is similar to those reported in single-crystalline BFO/FM bilayers. After the exploration of magnetic field cooling, the temperature dependent exchange bias can be explained considering two contributions from both the interfacial spin-glass-like frustrated spins and the polycrystalline grains in the BFO layer. Moreover, obvious exchange bias training effect can be observed at both 5 K and room temperature and the corresponding results can be well fitted based on a recently proposed theoretical model taking into account the energy dissipation of the AFM layer.