Single-crystalline CrSb(0001) thin films grown by dc magnetron co-sputtering

TL;DR

This work reports the fabrication of high-quality single-crystalline CrSb(0001) thin films in the NiAs structure via dc magnetron co-sputtering, using a PtSb(0001) buffer on SrF2(111) to promote epitaxy. Structural and chemical characterization shows phase-pure, (0001)-oriented CrSb and PtSb with extremely low mosaicity, smooth interfaces, and near-stoichiometric composition. Electrical and magnetic measurements indicate metallic CrSb with no detectable anomalous Hall effect under the studied orientation, though the material remains a promising platform for exploring altermagnetism when symmetry is manipulated. The buffer-layer strategy is highlighted as a practical route to high-crystal-quality NiAs-type CrSb and may extend to related materials such as MnSb and MnTe for spintronic investigations.

Abstract

The recent discovery of altermagnetism has sparked renewed interest in the growth of epitaxial films of the NiAs-phase polymorph of CrSb. This paper describes the magnetron sputtering-based fabrication and characterization of high-quality single crystalline CrSb(0001) thin films supported by an isostructural nonmagnetic PtSb buffer. X-ray diffraction and scanning transmission electron microscopy show that the films are phase pure and possess a very high crystalline quality (mosaicity ~0.05deg), while also being free of extended crystallographic defects. Both scanning electron microscopy and atomic force microscopy confirm their smooth and homogeneous topography. Additionally, the elemental composition of our films was found to be close to stoichiometric via electron probe microanalysis and x-ray fluorescence. Thus, the developed samples represent an ideal platform for further investigation of the material properties of CrSb.

Figures (9)

• Figure 1: (a) Unit cells of PtSb and CrSb with lattice parameters in bulk crystals. Arrows attached to Cr atoms indicate the magnetic order. (b) Cross-sectional HAADF-STEM image of a polished SrF2(111) (substrate)/30 PtSb(0001) (buffer)/20 CrSb(0001) heterostructure with zone axis $[2\bar{1}\bar{1}0]$.
• Figure 2: X-ray diffraction symmetric radial scans of our optimized films, performed in the parallel beam geometry with the detector in scanning 1D mode and using Cu-K$\alpha_1$ radiation. The results are presented for films grown on both cleaved and polished SrF2(111) substrates and are vertically offset for clarity. The corresponding rocking curves of the 0004 Bragg peak, measured with the detector in 0D mode, are presented on the right side (using the same line colors). The curves show a full width at half maximum (FWHM) of $0.05\degree$ and $0.35\degree$ in cleaved and polished cases, respectively.
• Figure 3: 0002 and 0004 film peaks from the XRD symmetric radial scan of cleaved SrF2(111)/30 PtSb(0001)/20 CrSb(0001), with the detector in 0D mode. The diffraction signals can be simulated well using the kinematic multibeam model of diffraction.
• Figure 4: Pole figure for $\left\{1\bar{1}02\right\}$ ($r$-planes) of PtSb(0001)/CrSb(0001) shown in stereographic projection. The sample was aligned such that SrF2$[1\bar{1}0]$ corresponds to $\phi=0\degree$. Six evenly spaced $1\bar{1}02$ poles or diffraction maxima (circled in red) affirm the perfect 6-fold rotational symmetry of the (0001)-oriented hexagonal unit cells of both layers. The appearance of a pole at $\phi=0\degree$ implies PtSb/CrSb$[2\bar{1}\bar{1}0]$$\parallel$SrF2$[1\bar{1}0]$. PtSb and CrSb cannot be distinguished in this measurement due to their nearly identical lattice constants. A sketch on the right illustrates the $r$-plane orientation within the unit cell.
• Figure 5: Cross-sectional HAADF-STEM of PtSb(0001)/CrSb(0001) showing their mutual epitaxial compatibility. The bilayer was grown on polished SrF2(111). The corresponding crystal structure is overlaid on the images as a guide to the eye. Despite their isostructural nature, the two crystalline layers exhibit distinct Z-contrast due to the different atomic weights of Pt and Cr.