Magnetooptical Study of Spin-Orientation Phase Transition in NdFe3(BO3)4 Single Crystal

The magnetic field dependences of birefringence in a NdFe3(BO3)4 single crystal have been measured in the case where the direction of light propagation coincides with the trigonal crystal axis C3 (k ║ C3), and the external magnetic field is oriented along the second-order axis C2 (H ║ C2). In the temperature range, in which an incommensurate phase exists with the formation of a long-period antiferromagnetic helix, the strongly pronounced jumps in the field dependence of birefringence are revealed and identified as a first-order spin-orientation phase transition. The phase transition was accompanied by a hysteresis in the field dependences of birefringence. The H–T phase diagram for a NdFe3(BO3)4 single crystal has been plotted in the case where the magnetic field is oriented along the crystal axis  C2 (H ║ C2).