Effect Of Optical F - F Excitations On The Nd-Fe Exchange Interaction In Nd Ferroborate With Multiferroic Properties

We considered the effect of optical pumping at the f - f transitions frequency on d-f superexchange in the rare-earth antiferromagnetic ferroborate Nd0.5Gd0.5Fe3(BO3)(4) between Nd3+ ions in the excited states of the (4)G(5/2), (2)G(7/2), and Fe3+ in the ground state (6)A(1). In the ferroborate, d-f 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 f - f transitions I-4(9/2) <-> ((4)G(5/2) + (2)G(7/2)) in the Nd3+ ion, the nature of the d- f 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 FMordering under the d-f AFM interaction to AFM ordering under the FM interaction in the basal hexagonal plane.