Structure and magnetism of Ni$_{50}$Mn$_{50}$ monolayers on Cu$_{3}$Au(001)

The growth, structure and magnetism of equiatomic NiMn ultrathin films on Cu$_{3}$Au(100) and the magnetism of Fe/FeMn bilayers on this substrate were investigated. NiMn alloys in a concentration range around 50-50{\%} have an L1$_{0}$ structure with lattice constants a and c of 3,74 e 3,52 {\AA}, respectively. This NiMn-phase is antiferromagnetic (AFM), with high N\'{e}el temperature ($\sim $ 1070 K), being very interesting for ferromagnetic / antiferromagnet systems with exchange bias effect and, therefore, for magneto-electronic devices. Cu$_{3}$Au is an ordered fcc phase with lattice parameter of 3,75 {\AA}, a substrate with very good epitaxial relationship with L1$_{0}$ NiMn. The NiMn monolayers were grown by coevaporation, under molecular beam epitaxy conditions, and characterized in situ by RHEED, LEED, XPS, AES and MOKE. Structural analysis revealed the epitaxy and layer-by layer growth at room temperature. MOKE measurements suggest that the Fe/Ni$_{50}$Mn$_{50}$ bilayers present exchange bias, indicating that equiatomic NiMn films, as grown on Cu$_{3}$Au(100) at room temperature, is AFM, as expected for the L1$_{0}$.