Canted antiferromagnetism in phase-pure CuMnSb

Abstract

We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at ${T}_{\mathrm{N}}=55$ K and a second anomaly at a temperature ${T}^{*}\ensuremath{\approx}34$ K. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of $(3.9\ifmmode\pm\else\textpm\fi{}0.1)\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$, consistent with the effective moment inferred from the Curie-Weiss dependence of the susceptibility. Below ${T}_{\mathrm{N}}$, the Mn sublattice displays commensurate type-II antiferromagnetic order with propagation vectors and magnetic moments along $\ensuremath{\langle}111\ensuremath{\rangle}$ (magnetic space group $R[I]3c$). Surprisingly, below ${T}^{*}$, the moments tilt away from $\ensuremath{\langle}111\ensuremath{\rangle}$ by a finite angle $\ensuremath{\delta}\ensuremath{\approx}{11}^{\ensuremath{\circ}}$, forming a canted antiferromagnetic structure without uniform magnetization consistent with magnetic space group $C[B]c$. Our results establish that type-II antiferromagnetism is not the zero-temperature magnetic ground state of CuMnSb as may be expected of the face-centered cubic Mn sublattice.