High-temperature magnetic investigations on uranium compounds

We investigated the magnetic property of typical uranium compounds by measuring the magnetic susceptibility in an extended temperature range up to about 800 K. The magnetic susceptibility follows the Curie-Weiss law for a localized 5f²-electron compound UPd₃ and a ferromagnetic insulator UFe₄P₁₂. In most of the investigated compounds we observed a crossover effect of the 5f electrons from a low-temperature itinerant nature to a high-temperature localized one. This is found to be characteristic for ferromagnetic superconductors such as UGe₂ and UIr, and also for antiferromagnets like USb₂ or UNiSb₂. To assess an extension of this characteristic property in the uranium compounds we also investigated typical 5f-itinerant compounds like UGa₃ and UPtGa₅. The crossover effect is essentially important in heavy fermion compounds such as UPt₃, UPd₂Al₃ and URu₂Si₂. Even in the paramagnetic compound of UB ₄, the magnetic susceptibility is not temperature-independent, but approaches a 5f-localized tendency at high temperatures. Since the samples were single crystals, we were also able to trace the evolution of the magnetic anisotropy. The high-temperature anisotropic susceptibility data were analyzed on the basis of the crystalline electric field scheme.