Structural and magnetic asymmetry at the interfaces of an Ag/57Fe/Ag trilayer studied using x-ray standing wave based techniques

Abstract

Interfaces in magnetic multilayers play a decisive role in determining their structural and magnetic properties, which significantly impact the performance of the spintronic devices. This work investigates the bottom and top interfaces of a few-nanometer-thick sup(57)Fe layer in an Ag/sup(57) Fe/Ag trilayer. The subnanometer depth resolution was obtained using x-ray standing waves (XSWs) generated by an underlying [W/Si] sub(10) multilayer. Each interface was selectively probed by scanning the standing-wave antinodes across the trilayer by varying the x-ray incidence angle around the Bragg condition. Detailed depth-resolved structural and magnetic information was obtained by combining the x-ray fluorescence (XRF) with isotope-selective (sup(57) Fe) grazing-incidence nuclear resonance scattering (GINRS) under XSW conditions. The results reveal a pronounced asymmetry in the interfacial roughness; the sup(57) Fe-on-Ag interface exhibits a larger rms roughness of 9.7 plus minus 1.0 Angstrom, whereas the Ag-on- sup(57) Fe interface is comparatively smoother, with a roughness of 6.4 plus minus 1.0 Angstrom. Correspondingly, GINRS measurements probed distinct hyperfine fields at the two interfaces, consistent with the observed structural asymmetry. Temperature-dependent measurements reveal enhanced interfacial intermixing. Fe K-edge extended x-ray absorption fine structure spectroscopy combined with temperature-dependent magnetic measurements shows that annealing at 325 degrees C induces strong nanoscale intermixing, resulting in the formation of Fe nanoparticles embedded in Ag. These results demonstrate that XSW-assisted XRF and GINRS provide a powerful and interface-specific probe of buried structural and magnetic asymmetries, offering valuable insights for the design and optimization of spintronic multilayer nanostructures.