Correlation between exchange bias field and domain size of ferromagnetic layer in Mn-Ir/Co-Fe bilayers

In order to clarify the correlation between the exchange bias strength and magnetic domain structure in ferromagnetic/antiferromagnetic (AF) bilayers, ferromagnetic domain structure was observed at Co-L-3 edge for polycrystalline Mn-Ir/Co-Fe bilayers by using the x-ray magnetic circular dichroism photoelectron emission microscopy technique. From the observation for four different samples prepared with the respective thermal annealing procedures, a positive correlation was found between the strength of exchange bias field and the ferromagnetic domain size. Within the framework of single spin ensemble model, it was indicated that the larger size of AF domain, which means small distribution of fixing direction of AF spins, can induce the larger exchange bias field. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073659]