Band-theoretical prediction of magnetic anisotropy in uranium monochalcogenides

Magnetic anisotropy of the uranium monochalcogenides US, USe, and UTe is studied by means of fully relativistic spin-polarized band structure calculations within the local spin-density approximation. It is found that the size of the magnetic anisotropy is fairly large (similar or equal to 10 meV/unit formula), which is comparable to experiment. This strong anisotropy is discussed in view of a pseudogap formation, of which crucial ingredients are the exchange splitting of U 5f states and their hybridization with chalcogen p states Cf-p hybridization). An anomalous trend in the anisotropy is found in the series (US much greater than USe<UTe) and interpreted in terms of competition between localization of the U 5f. states and the f-p hybridization. It is the spin-orbit interaction on the chalcogen p stares that plays an essential role in enlarging the strength of the f-p hybridization in UTe, leading to an anomalous systematic trend in the magnetic anisotropy.