Magnetic model in multiferroic NdFe3(BO3)4 investigated by inelastic neutron scattering

We performed inelastic neutron scattering measurements on single crystals of NdFe3(BO311)4 to explore the magnetic excitations, to establish the underlying Hamiltonian, and to reveal the detailed nature of hybridization between the 4f and 3d magnetism. The observed spectra exhibiting a couple of key features, i.e., anticrossing of Nd and Fe excitations and anisotropy gap at the antiferromagnetic zone center, are explained by the magnetic model including spin interaction in the framework of weakly coupled Fe3+ chains, interaction between the Fe3+ and Nd3+ moments, and single-ion anisotropy derived from the Nd3+ crystal field. The combination of the measurements and calculations reveals that the hybridization between 4f and 3d magnetism propagates the local magnetic anisotropy of the Nd3+ moment to the Fe3+ network, leading to the determination of the bulk structure of both electric polarization and magnetic moment in the multiferroics of the spin-dependent metal-ligand hybridization type.