Molecular beam epitaxy of the half-Heusler antiferromagnet CuMnSb

We report the growth of CuMnSb thin films by molecular beam epitaxy on InAs (001) substrates. The CuMnSb layers are compressively strained (0.6 %) due to lattice mismatch. The thin films have a $\omega$ full width at half-maximum of 7.7 arcsec according to high resolution x-ray diffraction, and a root-mean-square roughness of 0.14 nm as determined by atomic force microscopy. Magnetic and electrical properties are found to be consistent with reported values from bulk samples. We find a Néel temperature of 62 K, a Curie-Weiss temperature of −65 K, and an effective moment of $5.9{\mu }_B/\mathrm{f}.\mathrm{u}.$ Transport measurements confirm the antiferromagnetic transition and show a residual resistivity at 4 K of $35\mu$Ω cm.

Figure 1

Evolution of the RHEED reconstructions during growth of CuMnSb along [110] and $\left[1\overline{\text{1}}0\right]$ crystal directions. Before CuMnSb growth, an InAs $2\times 4$ reconstruction is observed [(a),(d)]. This transforms to a blurry $2\times 2$ reconstruction at the growth start of CuMnSb [(b),(e)]. With CuMnSb growth, the $2\times 2$ reconstruction becomes sharper and more intense [(c),(f)]. Specular spot oscillations (g) with a period of half a unit cell confirm layer-by-layer growth.

Figure 2

High-resolution x-ray diffraction scans of the CuMnSb thin film. (a) $\omega -2\theta$ diffractogram of the symmetric (002) diffraction peak (blue dots) together with a full dynamical simulation (orange line). (b) Rocking curve of the (002) CuMnSb peak (blue dots) with the fitted Voigt profile (orange line). (c) Reciprocal space map of the asymmetric (224) diffraction peak. The relaxation triangle for the CuMnSb layer is also shown (red lines). The pseudomorphic CuMnSb layer shows no signs of relaxation.

Figure 3

Atomic force microscopy measurements of the Ru capped CuMnSb sample (a) and an InAs buffer (b). The surface of Ru on CuMnSb shows atomic steps in the [010] crystal direction and a root-mean-square roughness of 0.14 nm. A decreased Sb flux of $3.9\times {10}^{-8}\mathrm{mbar}$ leads to a formation of dots on the CuMnSb surface (c). Dots with a higher density are formed at the surface for an increased Sb flux of $4.3\times {10}^{-8}\mathrm{mbar}$ (d). The height of the steps is consistent with half a unit cell (InAs or CuMnSb), as can be seen in the line scan (e) taken through two of the steps seen in (a).

Figure 4

Projections of the CuMnSb and InAs crystal along the $\left[1\overline{\text{1}}0\right]$ direction are superimposed on the STEM images [(a) and (b)]. For this orientation, only atoms of the same species are aligned along the line of sight. The color assignment is as follows: Sb, dark green; Cu, red; Mn, blue; In, magenta; As, light green; Ru, gray. The Ru is found to grow ordered on the CuMnSb (a). The interface between InAs and CuMnSb (b) shows a clean transition between the two materials. Both layers show a high degree of order and match the overlayed crystal. A model of the CuMnSb unit cell is depicted in (c). Larger area scans can be found in the Supplemental Material [19].

Figure 5

(a) Temperature dependence of the susceptibility during cooldown at 1 T. The cusp at 62 K marks the transition from paramagnetic to antiferromagnetic behavior ($T_{\text{N}}$). (b) Temperature-dependent inverse susceptibility during cooldown at 1 T. The lines indicate the Curie-Weiss behavior in the two temperature regimes with linear behavior of the inverse susceptibility. (c) Temperature dependence of resistivity of the CuMnSb thin film during warmup in zero field. The transition from antiferromagnetic to paramagnetic phase ($T_{\text{N}}$) is clearly indicated by a kink at 62 K. The inset shows raw data of the sample without substraction of the comparison signal.