Magnetic structure of Fe/Gd multilayers determined by resonant x-ray magnetic scattering

Abstract

The magnetic structures of a $({\mathrm{F}\mathrm{e}/\mathrm{G}\mathrm{d})}_{15}$ multilayer are determined by resonant x-ray magnetic scattering using circular polarized light of energies tuned close to the Gd L and the Fe K absorption edges. Difference superlattice Bragg peaks observed by flipping the photon helicity show that the magnetic moments of the Gd layers are directed antiparallel to the in-plane applied field at temperatures higher than 180 K, and are twisted below. The local Gd magnetizations in each 5.4-nm-thick layer are highly nonuniform in both magnitude and twist angle in the out-of-plane direction: the interface sublayers nearly fully magnetize at room and low temperatures under the influence of the adjacent Fe magnetizations, whereas the central sublayers show measurable spontaneous magnetizations at 200 K and below. An application of the $1\ensuremath{-}{(T/T}_{c})$ law shows a reduced Curie temperature ${(T}_{c}=214\mathrm{K})$ compared with bulk Gd for the central sublayers, while ${T}_{c}=1023\mathrm{K}$ for the interface sublayers. The interface and central sublayers exhibit distinct twist behaviors as a function of temperature below the compensation temperature, indicating the short-range nature of the Fe-Gd interaction. The element-specific resonant x-ray scattering confirmed the antiferromagnetic arrangement of the Gd and Fe moments at room temperature.