Optical spectra, crystal-field parameters, and magnetic susceptibility of multiferroicNdFe3(BO3)4

Abstract

We report high-resolution optical absorption spectra for NdFe 3 (BO 3 ) 4 trigonal single crystal which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering T N = 33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd 3+ 84 Kramers doublets. We perform crystalfield calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g-factors. In particular, the values g ⊥ = 2.385, g || = 1.376 were found for the Nd 3+ ground-state doublet. We obtain B loc =7.88 T and |J FN |= 0.48 K for the values of the local effective magnetic field at liquid helium temperatures at the Nd 3+ site and the Nd -Fe exchange integral, respectively, using the experimentally measured Nd 3+ ground-state splitting of 8.8 cm -1 . To check reliability of our set of crystal field parameters we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe 3+ ions J nn = -6.25 K (intrachain interactions) and J nnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with the experimental data.

Magnetic model in multiferroicNdFe3(BO3)4investigated by inelastic neutron scattering

“…The energy widths of the excitations at ω = 0.57 meV and 1.3 meV are broader than the experimental resolution. The energy split of 0.98 meV and the energy gap of 0.57 meV are consistent with the magnetic excitations reported from ESR measurement [28] and optical spectroscopy [29].…”

“…It also detected lifting of the Kramers doublet of the Nd 3+ ion due to the molecular field from the neighboring Fe 3+ ions. Optical spectroscopy provided the energy levels of the crystal field of the Nd 3+ ion and determined the parameters of the crystal field Hamiltonian [29].…”

Structural and magnetic investigations of single-crystalline neodymium zirconate pyrochloreNd2Zr2O7

“…Parameters of the free ion Hamiltonian h FI were taken from Ref. [51]. The initial values of the CF parameters were calculated in the framework of the exchange charge model [52,53] by making use of the parameters of the crystal lattice determined in the present work (see column A in Table IV).…”

Switching of Magnons by Electric and Magnetic Fields in Multiferroic Borates

“…According the optical experiments [66,67], in the iron borates the splitting of the ground rare-earth doublets are close to the magnon frequencies of the magnetic Fe-subsystem. Therefore, not only the static properties of the iron borates are strongly influenced by the rare-earth [54][55][56]58], but also the magnetic modes in these systems are strongly coupled.…”