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Structural studies by means of powder X-ray diffraction and single-crystal neutron diffraction show that URhGe crystallizes in the orthorhombic TiNiSi-type of structure. Combined magnetic, electrical-transport and thermal studies performed for the first time on a single crystal confirm ferromagnetic order of URhGe below 9.6 K. In contrast to previous powder neutron-diffraction experiments, our single-crystal results point to collinear ferromagnetic order of U moments of 0.35±0.08 μ B confined to the b–c plane, i.e. with no component along the a -axis, which is the hard-magnetization direction in URhGe. Our findings regarding the magnetic properties are in good agreement with theoretical first-principle calculations.

URhGe crystallizes in the orthorhombic TiNiSi-type of structure and has been studied untill now only in polycrystalline form. Here, we report on the low-temperature specific heat of URhGe measured on a single crystal. The compound orders ferromagnetically at T C =9.6 K. Because of this low magnetic-ordering temperature, the specific heat c p cannot be described by the usual expression γT + aT 3 , also at low temperatures. Up to 7 K, c p is satisfactorily described by the relationship γT + bT 2 , which must be associated with the temperature depenedence of the magnetization in this temperature interval. The value of γ amounts to 164 mJ/mol U K 2 . We have also studied the effect on c p of an external magnetic field applied along the principal axes. The results are discussed in terms of the strong magnetic anisotropy of URhGe.