  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.
