Cubic MnSb: Epitaxial growth of a predicted room temperature half-metal

Epitaxial films including bulklike cubic and wurtzite polymorphs of MnSb have been grown by molecular beam epitaxy on GaAs via careful control of the Sb${}_4$/Mn flux ratio. Nonzero-temperature density functional theory was used to predict ab initio the half-metallicity of the cubic polymorph and compare its spin polarization as a function of reduced magnetization with that of the well known half-metal NiMnSb. In both cases, half-metallicity is lost at a threshold magnetization reduction, corresponding to a temperature $T^{*}<T_C$. This threshold is far higher for cubic MnSb compared to NiMnSb and corresponds to $T^{*}>350$ K, making epitaxial cubic MnSb a promising candidate for efficient room temperature spin injection into semiconductors.

Figure 1

Nonzero-$T$ electronic structure theory for MnSb and NiMnSb. The curves show the calculated Fermi level spin polarization $P_{\text{DOS}}$ as a function of magnetization reduction for $c$-MnSb (red squares) and NiMnSb (blue diamonds), while the inset table summarizes calculated $T_C$ values from DLM-DFT. The experimental lattice parameter was assumed for $c$-MnSb, and the value used for NiMnSb matched that of Ref. 12. The vertical line labeled RT represents room temperature, assuming the experimental $T_C$ of NiMnSb for both materials.

Figure 2

Spin-polarized DOS for $c$-MnSb at different magnetizations $M\left(T\right)$ calculated by DLM-DFT at the experimental lattice parameter. The three curves correspond to $T=0$ K (blue dash), $T=T^{*}$ (red dash-dot), and $T=T_C$ (black solid line): the upper panel shows majority spin DOS and the lower minority spin DOS.

Figure 3

TEM data for polymorphic MnSb films on GaAs(111). A typical bright-field image (a) and Fourier transforms from individual regions (b) are labeled with constituent phases, while a high resolution micrograph of the $c$-MnSb/$n$-MnSb boundary shows a sharp epitaxial interface.