XMCD study of Mn-Ir/Co-Fe bilayers with giant exchange anisotropy

摘要

Exchange anisotropy is one of indispensable physical phenomena to realize recent high density magnetic storage devices. In order to understand the mechanism of exchange anisotropy in terms of spin structure, studies by means of X-ray magnetic circular dichroism (XMCD) are nowadays done for ferromagnetic (FM)/ antiferromagnetic (AFM) bilayer systems. The XMCD can detect uncompensated spins of AFM, and makes it possible to know the magnetization process of AFM layer. Ohldag et al. reported the correlation between exchange bias and pinned interfacial AFM spins through the XMCD studies for several exchange biased bilayer systems[1]. They concluded that the observed exchange anisotropy energy, J{sub}K, is dominated by the ideal interfacial coupling energy, J, between the FM and the AFM layers. The experimental fact, they found and deduced the above conclusion from, is that the pinned interfacial spins is always 4% of the interface layer, regardless of the exchange bias strength. It thus examines their thesis to compare the vertical offset of hysteresis loop of uncompensated AFM spins, which corresponds to the pinned interfacial spins, for the bilayer systems having same J and different J{sub}K. From this viewpoint, Mn{sub}75Ir{sub}25/Co-Fe bilayer is a favorable system, because its J{sub}K remarkably enhances to be a giant value exceeding 1erg/cm{sup}2 with promoting chemical ordering of Mn and Ir atoms[2]. But the J will remain constant against the enhancement of J{sub}K, since the atomic ordering of Mn and Ir does not change the chemical composition at the interface. In the present study, we therefore measured element specific magnetic hysteresis (ESMH) loops for Mn-Ir/Co-Fe bilayers with different chemical ordering of Mn-Ir layer by XMCD technique.