Lateral grain size effect on exchange bias in polycrystalline NiFe/FeMn bilayer films

This study explores the effect of lateral grain size on the exchange bias in the magnetron sputtered NiFe(5 nm)/FeMn(20 nm) bilayer films. The thicknesses of ferromagnetic (NiFe) and antiferromagntic (FeMn) layers were kept constant in the study. The lateral grain size variation was induced by increasing Ta buffer layer thickness. The cross-sectional transmission electron microscopy revealed that bilayers deposited on thicker Ta buffer layers have larger lateral grain diameter. Grain-to-grain epitaxy from buffer layer controls lateral grain size at NiFe/FeMn interface. A large increase in exchange bias field was observed with increasing thickness of Ta buffer layer, which is attributed to the enhanced ferromagnetic/antiferromagnetic coupling originated from larger interface lateral grain area.