Electron correlation effects and ferromagnetic order in β-UB2C

Measurements of the magnetic susceptibility, magnetization, electrical resistivity, magnetoresistance, specific heat, thermoelectric power and neutron powder diffraction on a polycrystalline sample of β-UB2C are reported. It is found that this compound with enhanced electronic specific-heat coefficient is a ferromagnet below TC = 74.5(0.5) K. At 1.5 K the ordered magnetic moment of the uranium ions is found to be 1.12(1) μB (U1 in 3b) and 1.03(1) μB (U2 in 6c), respectively. The uranium moments are close to the ab-plane (Φ = 470 and Θ = 84 deg.) forming ferromagnetic chains parallel to the hexagonal c-axis. In addition to the ferromagnetic transition, we found a characteristic temperature T* = 37 K, at which both the electrical resistivity and specific heat show anomalies. The thermoelectric power is positive and displays a maximum at 12 K. The observed features are compared to those of ferromagnetic UGe2 and UIr, known as superconductors under pressure. We discuss the experimental data in terms of strong electron correlation effects