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

Abstract

We present the depth-resolved nuclear resonance reflectivity (NRR) studies of the magnetization evolution in [ 57 Fe(3 nm)/Cr(1.2 nm)] 10 multilayer under the 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 the results. For the first time we show that the azimuth angle, which is used in all papers devoted to the magnetization profile determination, has more complicated physical sense due to the partially coherent averaging of the scattering amplitudes from magnetic lateral domains. We describe the way 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 Fe layers at increasing applied field.

Nuclear resonance reflectivity from a [57Fe/Cr]30multilayer with the Synchrotron Mössbauer Source

“…The integration can be carried out either electronically or by broadening the linewidth of the SMS using small deviations from the nuclear Bragg conditions [an explanation of different adjustments of the SMS is given by Potapkin et al (2012)]. The NRR curves are very important for characterization of the magnetic ordering in multilayers (see, for example, Toellner et al, 1995;Bottyá n et al, 1998;Andreeva et al, 1999;Kalska et al, 2001;Lindgren et al, 2001;Rö hlsberger et al, 2002;Diederich et al, 2007;Couet et al, 2009;Ś lę zak et al, 2010;Gupta et al, 2010;Andreeva et al, 2015), because contrary to the X-ray reflectivity curves they are sensitive to the magnetic structure of the multilayers.…”

“…The natural perfect collimation and brightness of SR allowed for measurements of the reflected intensity over a large angular scale. The detection of periodicity in magnetic multilayers (or isotopic periodicity) became possible by observation of the 'magnetic' or 'isotopic' maxima on the NRR angular curve (Chumakov et al, 1993;Toellner et al, 1995;Deá k et al, 1999;Gupta et al, 2005Gupta et al, , 2008Rennhofer et al, 2006;Diederich et al, 2007;Andreeva et al, 2015). The NRR curves were measured using the time gating, i.e.…”

“…Polarization properties of the amplitude of the nuclear resonant scattering in the presence of the hyperfine splitting of nuclear levels make the reflectivity theory much more complicated compared with X-ray reflectivity theory. The 4 Â 4-matrix theory of Mö ssbauer reflectivity from multilayers (general for the energy and time domains, but developed initially for experiments with radioactive sources in the energy domain) has been developed and presented in many papers (Andreeva & Rosete, 1986;Irkaev et al, 1993b;Rö hlsberger, 1999;Andreeva et al, 2015). Peculiarities in the reflectivity time spectra, measured with -polarized SR for various angles of the incident beam and different hyperfine field arrangements in the multilayer, have been thoroughly analyzed Rö hlsberger et al, 2003;Andreeva & Lindgren, 2005;Andreeva et al, 2007).…”

“…Peculiarities in the reflectivity time spectra, measured with -polarized SR for various angles of the incident beam and different hyperfine field arrangements in the multilayer, have been thoroughly analyzed Rö hlsberger et al, 2003;Andreeva & Lindgren, 2005;Andreeva et al, 2007). Specific patterns of the reflectivity time spectra at various grazing angles and Bragg maxima of the reflectivity from periodic multilayers have been effectively used for the description of the magnetization depth-profiles in the investigated samples (see, for example, Rö hlsberger et al, 2003;Ś lę zak et al, 2010;Andreeva et al, 2015). For the data analysis the program package REFTIM has been developed and uploaded to the ESRF scientific software web site (Andreeva, 2008;Andreeva et al, 2016b).…”

Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance reflectivity

“…In some systems the 90 o initial orientation of the two magnetic sub-systems have been discovered [11][12][13][14], supported by the bilinear-biquadratic formalism or specific proximity magnetism model ( [15][16], and review [8]). However, the theoretical modeling and the more sophisticated experimental techniques, giving the depth resolved magnetization profiles, like polarized neutron reflectivity (PNR) or nuclear resonance reflectivity (NRR), present a more complicated picture of the depth resolved magnetization reorientations including the layer-by-layer twisting of the magnetization in each magnetic sub-systems [17][18][19][20][21][22][23][24][25][26][27].…”