Paramagnetic magneto-optical activity f-f transitions in HoFe_3(BO_3)_4 and HoAl_3(BO_3)_4 single crystals

摘要

Absorption and magnetic circular dichroism (MCD) spectra of HoFe3(BO3)(4) and HoAl3(BO3)(4) single crystals were measured as a function of temperature in the range of 90-293 K. Based on integrals of f-f absorption and MCD bands, temperature dependences of the paramagnetic magneto-optical activity (MOA) of f-f transitions were obtained for the first time. It was revealed that MOA of the same f-f transitions in the studied crystals were substantially different and their temperature dependences did not follow the Curie-Weiss law in contrast to the properties of allowed transitions. The observed phenomena were accounted for as a consequence of the nature of f-f transitions allowance. In temperature dependences of the MOA of two transitions the singularities were revealed, which indicated to some local structural distortions in the corresponding excited states.