Incommensurate antiferromagnetic phase in UNiGe

By specific-heat, magnetization, electrical resistivity, and neutron-diffraction measurements on a single crystal we have confirmed that UNiGe orders antiferromagnetically below 50.5 K into an incommensurate phase with q=(0,1/2,-1/2)±(0,δ,δ), δ∼0.15. δ decreases continuously with decreasing temperature to ∼0.123 at 41.5 K, where the incommensurate phase vanishes in a first-order phase transition and a commensurate antiferromagnetic structure with q=(0,1/2,1/2) sets in and remains stable down to the lowest temperatures. If a magnetic field sufficient to induce a metalmagnetic transition (1--5 T) is applied along the c axis, both antiferromagnetic phases are transformed to an uncompensated AF phase with q=(0,1/3,1/3) yielding a nonzero magnetization M∼1/3xMS. The latter structure is destroyed and a complete alignment of U moments is achieved in fields above 10 T. The strikingly different B-T diagrams observed for a magnetic field applied along different crystallographic directions reflect strongly anisotropic exchange interactions