Electronic properties of a UIrGe single crystal

Structural study by means of x-ray powder diffraction and Laue technique show that UIrGe crystallizes in the orthorhombic TiNiSi-type structure. Magnetic measurements reveal a huge magnetic anisotropy in UIrGe with the hard magnetization axis along the a axis, i.e., along the direction of U-U zig-zag chains. Comprehensive magnetic, electrical-transport, thermopower, and thermal studies on a single crystal indicate the magnetic order of UIrGe below 15.8 K with an additional transition at 14.1 K. Magnetic and transport measurements on the polycrystalline sample, however, suggest that UIrGe orders magnetically at 16.4 K. All anomalies shift towards lower temperatures with increasing magnetic field suggesting that an antiferromagnetic ground state takes place in UIrGe at low temperatures. The drastically different low-temperature behavior of the electrical resistivity for single crystal ~increasing with decreasing temperature! as compared with that for the polycrystalline sample ~electrical resistivity decreases with lowering temperature! suggests different physical properties of bulk and surface areas. Resistivity and thermoelectric measurements indicate that a small gap across a part of the Fermi surface is established in the case of the single crystal. @S0163-1829~99!00237-4#