Effect of spin glass frustration on exchange bias in NiMn/CoFeB bilayers

Exchange bias in ferromagnetic/antiferromagnetic systems can be explained in terms of various interfacial phenomena. Among these spin glass frustration can affect the magnetic properties in exchange bias systems. Here we have studied a NiMn/CoFeB exchange bias system in which spin glass frustration seems to play a crucial role. In order to account the effect of spin glass frustration on magnetic properties, we have performed the temperature and cooling field dependence of exchange bias. We have observed the decrease of exchange bias field (HEB) with cooling field (HFC) whereas there is not significant effect on coercive field (HC). Exponential decay of HEB and HC is found in these exchange bias systems. Further, training effect measurements have been performed to study the spin relaxation mechanism. We have fitted the training effect data with frozen and rotatable spin relaxation model. We have investigated the ratio of relaxation rate of interfacial rotatable and frozen spins in this study. The training effect data are also fitted with various other models. Further, we observed the shifting of peak temperature towards higher temperature with frequency from the ac susceptibility data.