Influence of magnetic ordering on electronic structure of Tb<Superscript>3+</Superscript> ion in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal

Optical absorption spectra of trigonal crystal TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subs cript> have been studied in the region of <Superscript>7</Superscript>F<Subscript>6</Subscript> → <Superscript>5</Superscript>D<Subscript>4</Subscript> transition in Tb<Superscript>3+</Superscript> ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb<Superscript>3+</Superscript> excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb<Superscript>3+</Superscript> ion environment only in the excited state of the Tb<Superscript>3+</Superscript> ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb<Superscript>3+</Superscript> local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D <Subscript>3</Subscript> symmetry approximation) consists of two close singlet states of A <Subscript>1</Subscript> and A <Subscript>2</Subscript> type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subs cript> structural phase transition. The temperature interval of coexistence of the phases is about 3 K. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011