Structure and magnetism of epitaxial NiMn single layers and Co/NiMn bilayers on Cu$_{3}$Au(100)*

The structure of single-crystalline NixMn100-x (NiMn) ultrathin films on Cu3Au(100) and also the magnetic properties of Co films on the NiMn/Cu3Au(100) films have been investigated by multiple techniques. For 10 $\le $ x $\le $ 77, our results revealed good epitaxial, layer-by-layer growth at a substrate temperature of 300 K for all NiMn films with near equiatomic composition. The results indicate a face-centered tetragonal (fct) structure for NiMn, as expected for the L1o phase, and with the c-axis along the film normal. For the Co/NiMn bilayers, MOKE hysteresis loops show a thickness independent coercivity, suggesting no magnetic coupling at the Co/NiMn interface. Although the structural results indicate the formation of ftc NiMn in the equiatomic concentration range, we have no indication of antiferromagnetism for NiMn on Cu3Au(100) at room temperature. This is contrary to the observations for Co/NiMn on Cu(100).