  Polarized absorption spectra and magnetic circular dichroism (MCD) spectra of
Nd0.5Gd0.5Fe3(BO3)4 single crystal were measured in the range of 10000 - 21000
cm-1. The absorption spectra were studied as a function of temperature in the
range of 2 - 293 K and as a function of magnetic field 0 - 65 kOe at 2 K. The
excited 4f states of the Nd3+ ion were identified in terms of the irreducible
representations and in terms of |J,+-MJ> wave functions of the free atom. The
changes of the Lande factor during f-f transitions and the exchange splitting
of the ground and excited states were determined. It was found out that the
selection rules for electron transitions substantially changed in the
magnetically ordered state of the crystal. They are different for the different
transitions and they strongly depend on the orientation of the Fe sublattice
magnetic moment relative to the light polarization. It was revealed that the
local magnetic properties in the vicinity of the excited Nd3+ ion substantially
depended on its state. In particular, in some excited states a weak
ferromagnetic moment appears, the field induced reorientation magnetic
transitions occur and the changes of the local magnetic anisotropy type take
place. In some excited states the nonequivalent Nd3+ centers were found out.
