Magnetooptical Effects and Optical Absorption of FeBO₃ in the Region of ⁶A_1g → ⁴T_1g (⁴G), ⁴T_2g (⁴G) Transitions

The spectra of optical absorption, magnetic linear (MLD) and magnetic circular dichroism (MCD) in the weak ferromagnet FeBO₃ are investigated for transitions ⁶A_1g → ⁴T_1g(⁴G) and ⁶A_1g → ⁴T_2g(⁴G) at temperatures in the range of 90 to 300 K. It is shown that the temperature dependence of the absorption intensity and the zero moments of MLD and MCD of exciton–magnon lines for the transition → ⁴T_1g is described by an exponent exp (–T/T₀) and the MLD of these lines reveal an anomalous temperature dependence. In the region of the transition → ⁴T_2g, where there are no exciton–magnon lines, MLD is not observed at all. The strength of coupling of the exciton–magnon for the transition ⁴T_1g with even vibration E_g is determined and its independence of temperature is shown.