Field-induced spin reorientation in[Fe/Cr]nmultilayers studied by nuclear resonance reflectivity

Abstract

We present depth-resolved nuclear resonance reflectivity studies of the magnetization evolution in ${[^{57}\mathrm{Fe}(3\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/\mathrm{Cr}\phantom{\rule{0.16em}{0ex}}(1.2\phantom{\rule{0.16em}{0ex}}\mathrm{nm})]}_{10}$ multilayer under applied external field. The measurements have been performed at the station BL09XU of SPring-8 at different values of the external field (0--1500 Oe). We apply the joint fit of the delayed reflectivity curves and the time spectra of the nuclear resonance reflectivity measured at different grazing angles for enhancement of the depth resolution and reliability of results. We show that the azimuth angle, which is used in all papers devoted to the magnetization profile determination, has a more complicated physical sense due to the partially coherent averaging of the scattering amplitudes from magnetic lateral domains. We describe how to select the true azimuth angle from the determined ``effective azimuth angle.'' Finally we obtain the noncollinear twisted magnetization depth profiles where the spin-flop state appears sequentially in different $^{57}\mathrm{Fe}$ layers at increasing applied field.