The exchange bias effect in phase separatedNd1−xSrxCoO3 at the spontaneous ferromagnetic/ferrimagnetic interface

Abstract

We report new results for the exchange bias effect inNd1−xSrxCoO3 forx = 0.20 and 0.40, where the exchange bias phenomenon is involved with the ferrimagnetic (FI) state ina spontaneously phase separated system. The zero-field-cooled magnetization exhibits FI (TFI) and ferromagnetic(FM; TC)transitions at ∼23 and ∼70 K,respectively, for x = 0.20. Negative horizontal and positive vertical shifts of the magnetichysteresis loops are observed when the system is cooled throughTFI in a positive static magnetic field. A training effect is observed forx = 0.20, which could be interpreted satisfactorily by the spin configurationalrelaxation model. The unidirectional shifts of the hysteresis loops asa function of temperature exhibit an absence of exchange bias aboveTFI forx = 0.20.Analysis of the cooling field dependence of the exchange bias field and magnetization indicatesthat the FM clusters consist of a single magnetic domain with an average size of around∼20 and∼40 Å forx = 0.20 and 0.40, respectively. The sizes of the FM clusters are close to the percolation threshold forx = 0.20; these grow and coalesce to form the bigger size forx = 0.40 resulting in a weak exchange bias effect.