Nanoscale-Thick Ni-Based Half-Heusler Alloys with Structural Ordering-Dependent Ultralow Magnetic Damping: Implications for Spintronic Applications

Atomic ordering and its consequence on the crystal structure are fundamental issues in the application of half-metallic Heusler alloys considered as a high spin-polarized electron source. NiMnSb is a promising half-metallic half-Heusler alloy for spintronic devices due to its low magnetic damping, non-centrosymmetric crystal structure, and rich anisotropies. Here, we report a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate. High temperature deposition is a crucial parameter for crystal growth and magneto-dynamic properties such as damping, anisotropy, magnetization, etc. After investigating the ferromagnetic resonance (FMR) spectroscopy using a time-resolved magneto-optical Kerr (TRMOKE) microscope and calculating the crystal structure using VESTA and the density of states from first-principles calculations, we discuss how the deposition temperature influences the crystal ordering, damping, and magnetization. Ultralow Gilbert damping with high anisotropic field and saturation magnetization were found for the highly ordered C1_b structured nano-scale thick NiMnSb film deposited at 573 K. We also found quite nice agreement between theoretical and experimental data of crystal ordering and damping that explains how the ordering affects the magnetic parameter as well as sample quality. Furthermore, the negative anisotropic magnetoresistance ratio implies the robust bulk half-metallicity. Such unique combination of highly ordered half-metallic NiMnSb alloy in the nano-scale regime with ultralow damping can be regarded as an advantage for applications in spintronic devices.