Electronic properties of UX3 (X = Ga, Al, and Sn) compounds in high magnetic fields:: Transport, specific heat, magnetization, and quantum oscillations

We have performed measurements of the specific heat and resistivity in static magnetic fields up to 12 T, as well as magnetic measurements in a static field of 0.1 T and in pulsed fields up to 50 T on high-quality UX3 (X= Ga, Al, and Sn) single crystals. The behavior of the electronic specific heat coefficients in applied field gamma(B) either remains nearly constant or increases as B increases and is inconsistent with the expectations of the single-impurity model. For UGa3, different de Haas-van Alphen (dHvA) frequencies are observed above and below a magnetic transition at a field B(M)similar to 12 T at T similar to 0.5 K, indicating that a major reconstruction of the Fermi surface occurs. Neither USn3 nor UAl3 exhibited a magnetic transition in fields to 50 T, and only a single weak dHvA frequency was observed in these compounds. The difference between the behavior of the UX3 compounds can be attributed to the degree of hybridization of the 5f orbitals with the conduction electron orbitals. UGa3 behaves as an itinerant Sf-electron system, while UAl3 has a tendency to localization, but is still relatively delocalized. USn3 is a heavy fermion compound. Concurrent to our experimental investigations we have performed calculations of the energy band structures of the three compounds. Owing to the delocalized 5f behavior of UGa3, and also of UAl3, we find that an itinerant, energy band approach explains the dHvA frequencies of antiferromagnetic UGa3 and paramagnetic UAl3 reasonably well. For UGa3 an unusual sensitivity of the magnetic moment to the magnetic structure and the lattice parameter occurs, providing evidence that UGa3 is an unique example of an itinerant uranium-based antiferromagnet. [S0163-1829(99)04321-0].