UPtAl is a ferromagnet with a spontaneous magnetic moment Ms = 1.38 μB/f.u. directed along the hexagonal c axis and Curie temperature TC = 43.5 K. The uniaxial magnetocrystalline anisotropy is very strong, the estimated anisotropy field Ba exceeds 290 T. In a thermally-demagnetized sample the initial susceptibility along the c axis is very low for a wide field interval below a critical field Bst. Then the magnetization increases abruptly and saturates in a rather narrow field interval. The low-temperature hysteresis loop is almost rectangular with a 100% remanent magnetization. The coercivity (Bc = 0.7T at 1.7K) weakens rapidly with increasing temperature and vanishes at 20 K. A zero-field cooled sample exhibits a large thermal hysteresis. In the vicinity of Bst and Bc, a very pronounced magnetic viscosity is observed. As the main mechanism of the magnetic hysteresis we propose the pinning of domain walls which are very narrow due to the huge anisotropy and a relatively weak exchange interaction. The susceptibility as a function of temperature in paramagnetic range obeys a Curie-Weiss law with an effective magnetic moment μeff = 2.85 μB/f.u. The paramagnetic Curie temperatures Θp observed in fields applied along the a- and the c-axis differ considerably (-375 and 46 K, respectively) reflecting the fact that the huge uniaxial magnetic anisotropy persists in paramagnetic state. The electrical resistivity of UPtAl is rather isotropic. The large magnetic contribution to resistivity is due to a strong interaction of conduction-electron states with the narrow 5f-band states responsible for U magnetic moments in UPtAl. Up to T = 30 K, the temperature dependence of resistivity obeys a quadratic law ρ(T) = ρ0 + AT2 with A = 0.061 μΩ·cm/K2. UPtAl has an enhanced electronic specific-heat coefficient γ = 69 mJ/mol·K2. The correlation between A and γ fits to the Kadowaki-Woods plot.
ASJC Scopus subject areas
- Physics and Astronomy(all)