Training effect of exchange bias in La0.67Sr0.33MnO3/SrTiO3 superlattice

The training effect of exchange bias has been observed in the superlattice consisting of ferromagnetic La0.67Sr0.33MnO3 and non-magnetic SrTiO3 layers. The exchange field shows an approximately power-law decrease with an increase in the number of hysteresis loop measurements. The vertical shift of the hysteresis loop reveals the existence of the net uncompensated spins at the interface between the La0.67Sr0.33MnO3 and the SrTiO3 layers. The irreversibility of magnetization measurements gives clear evidence that the interfacial spins will be frozen at low temperature. It is suggested that the frozen uncompensated spins at the interface are responsible for the shift of the hysteresis loop and the training effect of exchange bias might be a result of the relaxation process of those interfacial spins when the superlattice is consecutively field-cycled.