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Involved people: G. Amoretti, S. Carretta, P. Santini
The physical interest in actinide compounds is due not only to their nuclear properties, but also to the rich and unusual magnetic and electronic properties. The peculiar phenomena occurring in these systems have to be ascribed to the role of 5f electrons, which show various degrees of localization in the different compounds, ranging from completely localized to itinerant band-like situations. The degree of localization also depends on external parameters such as, e.g. temperature or pressure. In this respect, these compounds resemble 3d compounds, but they differ for the role of orbital degrees of freedom, which are not quenched by the crystal electric field. This results in a very great variety of peculiar and exotic physical properties, most of which are still awaiting a full theoretical comprehension. In particular, orbital degrees of freedom enable multipolar ordering to take place, i.e. a phase transitions characterized by order parameters with rank larger than one (e.g., electric quadrupole or magnetic octupole). For instance, we have proposed rank-5 magnetic-multipole order to occur in NpO2.
Qualitative picture of the arrangement of magnetic triakontadipoles (cones) and of the induced electric quadrupoles (ellipsoids) in the 4-sublattices triple-q ground state of NpO2.
We work in close collaboration with the Institute for Transuranium Elements in Karlsruhe.
Main research topics: