Depth-dependent ferromagnetic spin structure and asymmetric magnetization reversal in exchange-biased Fe/FeMn bilayers

Abstract Depth-dependent spin rotation of the Fe spins upon magnetisation reversal of the ferromagnetic layer in polycrystalline Fe/FeMn exchange-biased bilayers was investigated by using 57Fe probe layers and angular hysteresis loops constructed from in-field 57Fe conversion electron Mossbauer spectroscopy (CEMS) measurements and magnetometry. Our results provide evidence for the formation of an exchange-spring-like domain wall structure inside the ferromagnetic Fe layer during magnetisation reversal along the forward branch of the hysteresis loop (H values varying from positive to negative), and coherent reversal along the recoil branch (H varying from negative to positive). This result implies asymmetric magnetisation reversal for each branch of the hysteresis loop, as indicated by depth-resolved CEMS and vibrating sample magnetometry. These results are relevant for the development of more precise quantitative models for exchange bias in polycrystalline metallic systems with Mn-based antiferromagnets such as those used in spintronic applications.