Electronic properties of a UIrGe single crystal

Structural study by means of x-ray powder diffraction and Laue technique sh ow that UIrGe crystallizes in the orthorhombic TiNiSi-type structure. Magne tic measurements reveal a huge magnetic anisotropy in UIrGe with the hard m agnetization axis along the a axis, i.e., along the direction of U-U zig-za g chains. Comprehensive magnetic, electrical-transport, thermopower, and th ermal studies on a single crystal indicate the magnetic order of UIrGe belo w 15.8 K with an additional transition at 14.1 K. Magnetic and transport me asurements on the polycrystalline sample, however, suggest that UIrGe order s magnetically at 16.4 K. All anomalies shift towards lower temperatures wi th increasing magnetic field suggesting that an antiferromagnetic ground st ate takes place in UIrGe at low temperatures. The drastically different low -temperature behavior of the electrical resistivity for single crystal (inc reasing with decreasing temperature) as compared with that for the polycrys talline sample (electrical resistivity decreases with lowering temperature) suggests different physical properties of bulk and surface areas. Resistiv ity and thermoelectric measurements indicate that a small gap across a part of the Fermi surface is established in the case of the single crystal. [S0 163-1829(99)00237-4].