Peculiarities of the 4I9/2-(4G5/2+2G7/2) transition behavior in   Nd0.5Gd0.5Fe3(BO3)4 and local magnetic properties of the crystal in the   excited states
  Polarized absorption spectra of single-crystal Nd0.5Gd0.5Fe3(BO3)4 were studied in the region of transition 4I9/2-(4G5/2+2G7/2) in Nd3+ ion as a function of temperature (2-34 K) and magnetic field (0-65 kOe). Spectra of natural circular dichroism were measured in the range of 5-40 K. It was found out that the local magnetic properties in vicinity of the excited ion substantially depend on its state. In particular, a weak ferromagnetic moment appears in some excited states. It was found out that selection rules for electron transitions in magnetically ordered state substantially deviate from those in paramagnetic state of the crystal. They are different for different transitions and they are very sensitive to orientation of the sublattice magnetic moment relative to the light polarization. In the spectrum of the natural circular dichroism, the transition is revealed which is not observed in the absorption spectrum. 
A.V. Malakhovskii, S.L. Gnatchenko, I.S. Kachur, V.G. Piryatinskaya,   A.L. Sukhachev, V.L. Temerov
cond-mat.str-el cond-mat.mtrl-sci