Role of Cu in exchange bias in FeMn revealed with neutron scattering*

We observed an unusual behavior: a non-magnetic material, copper, modifies magnetic properties of antiferromagnetic FeMn in close proximity. Copper is responsible for the ``\textit{intrinsic}'' exchange bias (EB) observed in a multilayered system without a distinct, separate ferromagnetic (FM) layer: Ta(5 nm)/[FeMn(5-45 nm)/Cu(5 nm)]$_{10}$/Ta(5 nm) [1]. This EB occurs between pinned and unpinned uncompensated magnetization (UM) in the FeMn layers. The analysis of the remanent magnetization (M$_{\mathrm{R}})$ shows that the unpinned (ferromagnet-like) UM is distributed uniformly throughout FeMn [1]. Since the magnitude of the EB loop shift (H$_{\mathrm{E}})$ scales with the inverse thickness of the FeMn layer, this EB is clearly an interfacial phenomena. This behavior is similar to that described by Malozemoff's model for the bilayer (antiferromagnet-ferromagnet) EB systems [2]. Thus, the pinned UM should be located near the FeMn interface. Results of polarized neutron reflectometry that explain the role of Cu in the unusual magnetism in these FeMn/Cu multilayers will be presented. \\[4pt] [1] D. Kaya \textit{et al.}, J. Appl. Phys., \textbf{113}, 17D717 (2013).\\[0pt] [2] A.P. Malozemoff, Phys. Rev. B \textbf{35}, 3679 (1987), \textit{ibid}., \textbf{37}, 7673 (1988).