The exchange bias effect in phase separated NdSr CoO at the spontaneous ferromagnetic/ferrimagnetic interface

We report new results for the exchange bias effect in Nd SrCoO for x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the ferrimagnetic (FI) state in a spontaneously phase separated system. The zero-field-cooled magnetization exhibits FI (T) and ferromagnetic (FM; T) transitions at ∼23 and ∼70K, respectively, for x = 0.20. Negative horizontal and positive vertical shifts of the magnetic hysteresis loops are observed when the system is cooled through T in a positive static magnetic field. A training effect is observed for x = 0.20, which could be interpreted satisfactorily by the spin configurational relaxation model. The unidirectional shifts of the hysteresis loops as a function of temperature exhibit an absence of exchange bias above T for x = 0.20. Analysis of the cooling field dependence of the exchange bias field and magnetization indicates that the FM clusters consist of a single magnetic domain with an average size of around ∼20 and ∼40 for x = 0.20 and 0.40, respectively. The sizes of the FM clusters are close to the percolation threshold for x = 0.20; these grow and coalesce to form the bigger size for x = 0.40 resulting in a weak exchange bias effect. © 2009 IOP Publishing Ltd.