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 $T_{\mathrm{N}}=55\mathrm{K}$ and a second anomaly at a temperature $T^{\ast }\approx 34\mathrm{K}$. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of $(3.9\pm 0.1)\hat{I}{¼}_{\mathrm{B}}/f.u.$, 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 $⟨111⟩$ (magnetic space group $R[I]3c$). Surprisingly, below $T^{\ast }$, the moments tilt away from $⟨111⟩$ by a finite angle $\hat{I}´\approx 11^{\circ }$, 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.

14 pages, 15 figures