Magnetic, thermal, and transport properties of single-crystalline U3Fe4Ge4

Magnetic, thermal, and transport properties of a U3Fe4Ge4 single crystal have been studied. The compound crystallizes in the orthorhombic Gd3Cu4Ge4 structure type. U3Fe4Ge4 displays ferromagnetic order below the Curie temperature TC = 18 K. The magnetism originates from the uranium sublattice, as iron atoms have no ordered magnetic moments. U3Fe4Ge4 exhibits a pronounced easy-axis anisotropy with the anisotropy field exceeding 60 T. The spontaneous magnetic moment is Ms = 1.2 μB/f.u. at T = 2 K. Magnetic contribution to specific heat shows a gap excitation behavior with Δ = 4 meV, which can be related to the magnon gap due to the anisotropy. The Sommerfeld coefficient of the electronic specific heat is γ = 57 mJ/(mol-U K2) in the ordered state, whereas it is much higher (145 mJ/(mol-U K2) if derived from the paramagnetic state. Electrical resistivity has very high values on the mΩ cm range.

► U3Fe4Ge4 represents pure uranium magnetism as iron has no ordered magnetic moment.
► Magnetic, thermal, and transport properties were studied on a U3Fe4Ge4 single crystal.
► U3Fe4Ge4 is a strongly itinerant 5f ferromagnet.
► A strong easy-axis anisotropy is observed that results in a gap excitation behavior.