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 stat ic 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 in creases as B increases and is inconsistent with the expectations of the sin gle-impurity model. For UGa3, different de Haas-van Alphen (dHvA) frequenci es are observed above and below a magnetic transition at a field B(M)simila r 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 transi tion 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 compound s 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 experiment al investigations we have performed calculations of the energy band structu res of the three compounds. Owing to the delocalized 5f behavior of UGa3, a nd also of UAl3, we find that an itinerant, energy band approach explains t he dHvA frequencies of antiferromagnetic UGa3 and paramagnetic UAl3 reasona bly well. For UGa3 an unusual sensitivity of the magnetic moment to the mag netic structure and the lattice parameter occurs, providing evidence that U Ga3 is an unique example of an itinerant uranium-based antiferromagnet. [S0 163-1829(99)04321-0].