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 TN=55K and a second anomaly at a temperature T∗≈34K. Powder and single-crystal neutron diffraction establish an
ordered magnetic moment of (3.9±0.1)μB/f.u.,
consistent with the effective moment inferred from the Curie-Weiss dependence
of the susceptibility. Below TN, 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∗, the moments tilt away from ⟨111⟩ by
a finite angle δ≈11∘, 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.Comment: 14 pages, 15 figure