Canted antiferromagnetism in phase-pure CuMnSb

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 $T^{*} \approx 34~\mathrm{K}$. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of $(3.9\pm0.1)~\mu_{\mathrm{B}}/\mathrm{f.u.}$, 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 $\langle111\rangle$ (magnetic space group $R[I]3c$). Surprisingly, below $T^{*}$, the moments tilt away from $\langle111\rangle$ by a finite angle $\delta \approx 11^{\circ}$, 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.Comment: 14 pages, 15 figure

Magnetic properties of the noncentrosymmetric tetragonal antiferromagnet EuPtSi3_3

We report a comprehensive study of single crystals of the noncentrosymmetric rare-earth compound EuPtSi$_3$ grown by the optical floating-zone technique. Measurements of the magnetization, ac susceptibility, and specific heat consistently establish antiferromagnetic order of localized Eu2+ moments below the Néel temperature T$_N$=17 K, followed by a second magnetic transition at T$_{N1}$=16 K. For a magnetic field along the easy [001] axis, the magnetic phase diagram is composed of these two phases. For fields applied in the magnetically hard basal plane, two additional phases emerge under magnetic field, where the in-plane anisotropy is weak with [100] being the hardest axis. At the phase transitions, the magnetic properties exhibit hysteresis and discrepancies between differential and ac susceptibility, suggesting slow reorientation processes of mesoscale magnetic textures. Consistently, powder and single-crystal neutron diffraction in zero field identify magnetic textures that are modulated on a length scale of the order of 100 Å, most likely in the form of Néel-type antiferromagnetic cycloids

Low-temperature structural investigations of the frustrated quantum antiferromagnets Cs2Cu(Cl4−xBrx){\mathrm{Cs}}_{2}\mathrm{Cu}\left({\mathrm{Cl}}_{4-x}{\mathrm{Br}}_{x}\right)

Powder x-ray diffraction (PXRD) and single-crystal neutron scattering were used to study in detail the structural properties of the Cs2Cu(Cl4−xBrx) series, good realizations of layered triangular antiferromagnets. Detailed temperature-dependent PXRD reveal a pronounced anisotropy of the thermal expansion for the three different crystal directions of the orthorhombic structure without any structural phase transition down to 20 K. Remarkably, the anisotropy of the thermal expansion varies for different x, leading to distinct changes of the geometry of the local Cu environment as a function of temperature and composition. The refinement of the atomic positions confirms that for x=1 and 2, the Br atoms occupy distinct halogen sites in the [CuX4] tetrahedra (X = Cl, Br). The precise structure data are used to calculate the magnetic exchange couplings using density functional methods for x=0. We observe a pronounced temperature dependence of the calculated magnetic exchange couplings, reflected in the strong sensitivity of the magnetic exchange couplings on structural details. These calculations are in good agreement with the experimentally established values for Cs2CuCl4 if one takes the low-temperature structure data as a starting point