ANISOTROPIC MAGNETIC AND TRANSPORT-PROPERTIES OF UNIGE

Magnetism in UNiGe which adopts the orthorhombic TiNiSi type of struct ure 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 theta(p) equal to -98, 3 and 41 K for the a, b and c axis, respectively. Also the electrical resistivity is ani sotropic and reflects magnetic phase transitions at 41.5 and 50 K, in very good agreement with specific-heat data. An antiferromagnetic stru cture of U moments of about 1.4 mu(B) with a propagation vector q = (0 , 0.5, 0.5) can be concluded from neutron-diffraction studies at low t emperatures. Two metamagnetic transitions are observed in high-field m agnetization 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 magn etic moments in fields above the second transition. The magnetization measured at 35 T amounts to 1.45 mu(B)/fu. The huge magnetic anisotrop y is reflected in the weak linear magnetic response to fields along th e a axis yielding only 0.23 mu(B)/fu. at 35 T. The destruction of anti ferromagnetic ordering in high fields is accompanied by a reduction of about 80 % of the electrical resistivity. The huge magnetic anisotrop y and giant magnetoresistance which is also observed in other UTX comp ounds (T = transition metal, X = p-metal) can be understood in terms o f anisotropic 5f-ligand hybridization.