Nonuniform and sequential magnetization reversal via domain structure formation for multilayered system with grain size induced enhanced exchange bias

摘要: We report on the magnetization reversal in series of exchange-biased multilayers NiFe(10.0 nm)/[ Ir20Mn80(6.0 nm)/Co80Fe20(3.0 nm)] N studied by specular reflection and off-specular scattering polarized neutrons. All specimens are sputtered post-annealed at 530 K (i.e. above IrMn Neel temperature 520 K) Ar atmosphere before cooling to room presence a field 130 Oe which induces unidirectional anisotropy. find HEB is dependent upon number bilayers as it gradually increases from 0.33 kOe for N=1 considerably higher value upto ≈0.9 N=10. X-ray diffuse data reveal no significant variation lateral correlation length only weak dependence vertical rms interface roughness N. Atomic magnetic force microscopy, however, show strong reduction grain size accompanied distinct changes ferromagnetic domain structure. The enhancement exchange bias effect presumably related shrinking antiferromagnet due structural evolution multilayers. Polarized neutron reflectometry (PNR) measurements done different applied fields sweeping both branches hysteresis loop. spin-flip (SF) cross section N=10 3 samples diffusely scattered intensity appears approaches most intense where net vanishes. disappearance saturation indicates that process. proceeds sequentially starting with bottom (top) CoFe layer decreasing (increasing) along stack. each wall motion. Thus main result, we observe sequential symmetric concomitant in-plane fluctuations revealed indicate more complex mechanism than hitherto considered. Moreover, although decreases N=3 10 factor about four remains similar.