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

Magnetocaloric properties of (RE)3_3Ga5_5O12_{12} (RE=Tb,Gd,Nd,Dy)

We report the characteristic magnetic properties of several members of the rare earth garnet family, Gd$_3$Ga$_5$O$_{12}$ (GGG), Dy$_3$Ga$_5$O$_{12}$ (DGG), Tb$_3$Ga$_5$O$_{12}$ (TGG), and Nd$_3$Ga$_5$O$_{12}$ (NGG), and compare their relative potential utility for magnetocaloric cooling, including their minimal adiabatic demagnetisation refrigeration (ADR) temperatures and relative cooling parameters. A main objective of this work was to find potential improvements over the magnetocaloric properties of GGG for use in low temperature ADR cryostats. Using Tb$^{+3}$ and Dy$^{+3}$ in the RE-site offers in principle higher saturation magnetisation and Nd$^{+3}$ gives a lower de Gennes factor and therefore potentially low transition temperature. Our results show that Dy$_3$Ga$_5$O$_{12}$ yields an optimal relative cooling parameter ($RCP$) at low applied fields and a low transition temperature, which would allow for the design of more efficient ADR cryostats.Comment: 10 pages, 10 figures, submitted to Physical Review Applie

De Haas-van Alphen effect and Fermi surface properties of single crystal CrB2

We report the angular dependence of three distinct de Haas-van Alphen (dHvA) frequencies of the torque magnetization in the itinerant antiferromagnet CrB2 at temperatures down to 0.3K and magnetic fields up to 14T. Comparison with the calculated Fermi surface of nonmagnetic CrB2 suggests that two of the observed dHvA oscillations arise from electron-like Fermi surface sheets formed by bands with strong B-px,y character which should be rather insensitive to exchange splitting. The measured effective masses of these Fermi surface sheets display strong enhancements of up to a factor of two over the calculated band masses which we attribute to electron-phonon coupling and electronic correlations. For the temperature and field range studied, we do not observe signatures reminiscent of the heavy d-electron bands expected for antiferromagnetic CrB2. In view that the B-p bands are at the heart of conventional high-temperature superconductivity in the isostructural MgB2, we consider possible implications of our findings for nonmagnetic CrB2 and an interplay of itinerant antiferromagnetism with superconductivity.Comment: 8 pages, 4 figure

Ultra-high vacuum compatible induction-heated rod casting furnace

We report the design of a radio-frequency induction-heated rod casting furnace that permits the preparation of polycrystalline ingots of intermetallic compounds under ultra-high vacuum compatible conditions. The central part of the system is a bespoke water-cooled Hukin crucible supporting a casting mold. Depending on the choice of the mold, typical rods have a diameter between 6 mm and 10 mm and a length up to 90 mm, suitable for single-crystal growth by means of float-zoning. The setup is all-metal sealed and may be baked out. We find that the resulting ultra-high vacuum represents an important precondition for processing compounds with high vapor pressures under a high-purity argon atmosphere up to 3 bars. Using the rod casting furnace, we succeeded to prepare large high-quality single crystals of two half-Heusler compounds, namely, the itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb

Single crystal growth of CeTAl₃ (T = Cu, Ag, Au, Pd and Pt)

Abstract We report single crystal growth of the series of CeTAl3 compounds with T = Cu, Ag, Au, Pd and Pt by means of optical float zoning, where high crystal quality was confirmed in a thorough characterization process. With the exception of CeAgAl3, all compounds crystallize in the non-centrosymmetric tetragonal BaNiSn3 structure (space group: I4mm, No. 107), whereas CeAgAl3 adopts the related orthorhombic PbSbO2Cl structure (Cmcm, No. 63). An attempt to grow CeNiAl3 resulted in the composition CeNi2Al5. Low temperature resistivity measurements down to ∼ 0.1 K did not reveal evidence suggestive of magnetic order in CePtAl3 and CePdAl3. In contrast, CeAuAl3, CeCuAl3 and CeAgAl3 display signatures of magnetic transitions at 1.3 K, 2.1 K and 3.2 K, respectively. This is consistent with previous reports of antiferromagnetic order in CeAuAl3 and CeCuAl3 as well as ferromagnetism in CeAgAl3, respectively

High‐Pressure Studies of Correlated Electron Systems

Tuning the electronic properties of transition-metal and rare-earth compounds by virtue of changes of the crystallographiclattice constants offers controlled access to new forms of order. We review the development oftungsten carbide and moissanite Bridgman cells conceived for studies of the electrical resistivity up to 10GPa,as well as bespoke diamond anvil cells developed for neutron depolarization studies up to 20GPa. For the diamondanvil cells, the applied pressure changes as a function of temperature in quantitative agreement withthe thermal expansion of the pressure cell. A set-up based on focussing neutron guides for measurements of thedepolarization of a neutron beam by samples in a diamond anvil cell is described. Resistivity measurementsand neutron depolarization provide evidence of ferromagnetic order in SrRuO$_3$ up to 14GPa close to a putativequantum phase transition. Combining hydrostatic, uniaxial, and quasi-hydrostatic pressure, the emergenceof incipient superconductivity in CrB$_2$ is observed. The temperature dependence of the electrical resistivity inCeCuAl$_3$ is consistent with emergent Kondo correlations and an enhanced coupling of magneto-elastic excitationswith the conduction electrons at low and intermediate temperatures, respectively