Concentration- and thickness-dependent magnetic properties of NixMn100-x in epitaxially grown NixMn100-x/Ni/(Co/)Cu3Au(001)

Magnetic proximity effects in single-crystalline NixMn100-x/Ni(/Co) bilayers on Cu3Au(001) are investigated for in-plane (IP) and out-of-plane (OoP) magnetization by means of the longitudinal and polar magneto-optical Kerr effect. Attention is paid to the influence on concentration-and thickness-dependent antiferromagnetic ordering (T-AFM) and blocking (T-b) temperatures as well as the exchange bias field (H-eb). For all the NixMn100-x films under study in contact with IP Ni, increasing T-AFM is observed with decreasing Ni concentration from similar to 50 to similar to 20%, whereas only a slight change in T-AFM is observed for the OoP case. Between similar to 28% and similar to 35% Ni concentration, a crossover temperature exists below which T-AFM for the IP samples is higher than for the OoP samples and vice versa. T-b is higher for the IP case than for OoP, except for an equi-atomic NiMn film, while H-eb increases significantly for both magnetization directions with decreasing x. These results are attributed to: (i) a rotation of the non-collinear 3Q-like spin structure of NixMn100-x from the more-OoP to the more-IP direction for decreasing Ni concentration x, along with an associated increased magnetic anisotropy, and (ii) a smaller domain wall width within the NixMn100-x films at smaller x, leading to a smaller thickness required to establish exchange bias at a fixed temperature.