Pressure effects on the magnetic transitions in strongly-correlated-electron systems.

摘要

In this thesis, the pressure effects on the magnetic properties of strongly-correlated-electron systems (mostly compounds based on uranium, cerium, other rare earths and transition-metal oxides) were studied by means of both bulk and microscopic techniques. The bulk studies include magnetic, specific heat and magnetoresistance measurements. The microscopic investigations utilized neutron diffraction. In order to gain insight into the stability of the magnetic phases, the strength of exchange interactions and the mechanism underlying the relative stability of different possible phases of these materials, many of these studies were performed under multi-extreme conditions (low temperature, high magnetic field and high pressure). In general, we find relatively weak pressure dependence in compounds with localized unpaired electrons, while substantially larger pressure effects are found in more itinerant compounds.; Most of the strongly-correlated-electron systems studied here exhibit huge magnetocrystalline anisotropy. In the case of uranium compounds, we were able to establish that the large anisotropy is connected to the anisotropic 5f-ligand hybridization, while the anisotropy in cerium and other rare-earth compounds can be attributed to crystal-field effects.