Anisotropic magnetic and transport properties of UNiGe

Magnetism in UNiGe which adopts the orthorhombic TiNiSi type of structure with lattice constants a=700.7 pm, b =423.7 pm, c=720.7 pm is strongly anisotropic. The Curie-Weiss behaviour of the susceptibility above 80 K yields values of Θ_p equal to -98, 3 and 41 K for the a, b and c axis, respectively. Also the electrical resistivity is anisotropic and reflects magnetic phase transitions at 41.5 and 50 K, in very good agreement with specific-heat data. An antiferromagnetic structure of U moments of about 1.4 μ_B with a propagation vector q=(0, 0.5, 0.5) can be concluded from neutron-diffraction studies at low temperatures. Two metamagnetic transitions are observed in high-field magnetization data at 4.2 K in fields applied along the b (at 17 and 25 T) and c (at 3 and 10 T) axes yielding parallel alignment of the magnetic moments in fields above the second transition. The magnetization measured at 35 T amounts to 1.45 μ_B/f.u. The huge magnetic anisotropy is reflected in the weak linear magnetic response to fields along the a axis yielding only 0.23 μ_B/f.u. at 35 T. The destruction of antiferromagnetic ordering in high fields is accompanied by a reduction of about 80 of the electrical resistivity. The huge magnetic anisotropy and giant magnetoresistance which is also observed in other UTX compounds (T=transition metal, X=p-metal) can be understood in terms of anisotropic 5f-ligand hybridization