Direct observation of multivalent states and 4 f → 3d charge transfer in Ce-doped yttrium iron garnet thin films

Due to their large magneto-optic responses, rare earth-doped yttrium iron garnets, Y₃Fe₅O₁₂ (YIG), are highly regarded for their application potential in photonics and magnonics. Here, we consider the case of Ce-doped YIG (Ce-YIG), in which substitutional Ce³⁺ ions are expected to be magnetic because of their 4f¹ ground state. To investigate the impact of Ce-doping on the magnetism and electronic properties of the YIG parent compound, we exploited synchrotron x-ray spectroscopies. Using these element and site- specific spectroscopies, we demonstrate the emergence of an electron charge transfer from Ce 4f states specifically towards Fe 3d states at the tetrahedral sites of the YIG structure. As a consequence of the perturbation of the cation electronic states, the site-specific (Ce and Fe) sublattice magnetizations are disturbed in such a way that their respective magnetization hysteretis curves show atypical signatures, deviating from conventional magnetic hysteretic behavior. Our study establishes a step forward in the comprehension of the fundamental physical processes caused by rare-earth doping regarding YIG electronic and magnetic properties that, as aforementioned, is a prerequisite to further optimize and tailor the optical properties of these important materials.