Specific features of Nd3+ Kramers doublets’ splitting in an antiferromagnetic crystal NdFe3(BO3)4 in an external magnetic field

The optical absorption spectra of an easy-plane NdFe3(BO3)4 antiferromagnet are measured in the region of the 4I9/2 → 2H11/2 transition of the of Nd3+ ion. The study is performed in the 2–35 К temperature range, in external magnetic fields of up to 65 kOe directed both along the С3 axis and the basal plane of the crystal. The splitting values of the Nd3+ excited states in the exchange field of the Fe3+ subsystem and the g-factors of the 2H11/2 multiplet states are determined. The nontrivial dependences of the splitting of some Nd3+ states in a magnetic field indicate that these states have anisotropic Fe–Nd exchange interaction.