Element selective magnetism in Ho0.5Nd0.5Fe3(BO3)4 single crystal probed with hard X-ray magnetic circular dichroism

We present a study of a Ho0.5Nd0.5Fe3(BO3)4 single crystal aiming at understanding the roles of each magnetic sublattices in magnetic transitions at low temperatures. The crystal structure is determined to have the R32 symmetry in whole studied temperature range but the crystal appears to be racemic. Element selective magnetic properties studied with X-ray magnetic circular dichroism at the L2,3-edges of Ho and Nd, and at the Fe K-edge at T = 3 K under magnetic fields of ±17 T are compared with the results of macroscopic magnetization measurements in pure and substituted crystals. All three magnetic sublattices are shown to be strongly coupled and to undergo a spin-reorientation transition when magnetic field is applied along the trigonal c-axis. On the contrary, when magnetic field is applied in the ab-plane only the holmium atoms exhibit a sizeable magnetization jump. This result allows us to conclude that the spin-flop transitions observed in macroscopic magnetization curves and associated anomalies of electric polarization are due to the Ho3+ magnetic moment reorientation.