Effect of optical f - f excitations on the Nd-Fe exchange interaction in Nd ferroborate with multiferroic properties

Gavrichkov, Vladimir A.; Malakhovskii, Alexandr V.; Ovchinnikov, Sergey G. Physical Review B/ Phys. Rev. B 104, 064445 / DOI:https://doi.org/10.1103/PhysRevB.104.064445

We considered the effect of optical pumping at the ff transitions frequency on df superexchange in the rare-earth antiferromagnetic ferroborate Nd0.5Gd0.5Fe3(BO3)4 between Nd3+ ions in the excited states of the 4G5/2, 2G7/2, and Fe3+ in the ground state 6A1. In the ferroborate, df superexchange is directly related to the strong magnetoelectric coupling observed in the ground state of the material. We show that under optical pumping at the frequency of ff transitions 4I9/2(4G5/2+2G7/2) in the Nd3+ ion, the nature of the df interaction changes to FM. The phenomena can be explained by the occupation of the excited Nd3+ “spin pure” states with spin 1/2, or their mixing to the optically excited states with spin 3/2 due to the spin-orbit interaction. Near optically excited ions Nd3+, magnetic frustrations change from FM ordering under the df AFM interaction to AFM ordering under the FM interaction in the basal hexagonal plane.

DOI: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.064445