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The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic resonance (FMR) measurements and calculations from first principles to investigate how the composition of the epitaxially grown NiMnSb influences the magnetodynamic properties of saturation magnetization MS, Gilbert damping α, and exchange stiffness A. MS and A are shown to have a maximum for stoichiometric composition, while the Gilbert damping is minimum. We find excellent quantitative agreement between theory and experiment for MS and α. The calculated A shows the same trend as the experimental data, but has a larger magnitude. Additionally to the unique inplane anisotropy of the material, these tunabilities of the magnetodynamic properties can be taken advantage of when employing NiMnSb films in magnonic devices.

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NiMnSb is a ferromagnetic half-metal which, because of its rich anisotropy and very low Gilbert damping, is a promising candidate for applications in information tech- , we find that a variation in composition can change the strength of the four-fold anisotropy by more than an order of magnitude and cause a complete 90• rotation of the uniaxial anisotropy. This provides valuable flexibility in designing new device geometries.

Spin-dependent transport phenomena due to relativistic spin-orbit coupling and broken space-inversion symmetry are often difficult to interpret microscopically, in particular when occurring at surfaces or interfaces. Here we present a theoretical and experimental study of spin-orbit torque and unidirectional magnetoresistance in a model room-temperature ferromagnet NiMnSb with inversion asymmetry in the bulk of this half-Heusler crystal. Aside from the angular dependence on magnetization, the competition of Rashba-and Dresselhaus-type spin-orbit couplings results in the dependence of these effects on the crystal direction of the applied electric field. The phenomenology that we observe highlights potential inapplicability of commonly considered approaches for interpreting experiments. We point out that, in general, there is no direct link between the current-induced nonequilibrium spin polarization inferred from the measured spin-orbit torque and the unidirectional magnetoresistance. We also emphasize that the unidirectional magnetoresistance has not only longitudinal but also transverse components in the electric field: current indices which complicate its separation from the thermoelectric contributions to the detected signals in common experimental techniques. We use the theoretical results to analyze our measurements of the on-resonance and off-resonance mixing signals in microbar devices fabricated from an epitaxial NiMnSb film along different crystal directions. Based on the analysis we extract an experimental estimate of the unidirectional magnetoresistance in NiMnSb.