Raman scattering from phonons and magnons inRFe3(BO3)4

Abstract

Inelastic light scattering spectra of several members of the RFe3(BO3)4 family reveal a cascade of phase transitions as a function of temperature, starting with a structural, weakly first order, phase transition followed by two magnetic phase transitions. Those consist of the ordering of the Fe-spin sublattice revealed by all the compound, and a subsequent spin-reorientational transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice ordering leads to a strong suppression of the low energy magnetic scattering, and a multiple peaked two-magnon scattering continuum is observed. Evidence for short-range correlations is found in the 'paramagnetic' phase by the observation of a broad magnetic continuum in the Raman data, which persists up to surprisingly high temperatures.

Magnetodielectric and magnetoelastic coupling inTbFe3(BO3)4

“…21 We have done Raman spectroscopy measurements to look for direct evidence of spin-lattice coupling. According to the previous reports 7,22 there are 59 transverse optical modes that correspond to ⑀ ab , i.e., phonon modes corresponding to a TO mode propagating perpendicular to the c axis. We have checked the temperature dependence of these modes and observed that only two low-lying ones shift their frequency at low temperatures: the first one at 200 cm −1 and the second one at 260 cm −1 .…”

“…In the magnetically ordered phase Gd 4f-Fe 3d magnetic interactions cause a spinreorientation transition which is coupled to the dielectric constant via spin-lattice interaction. 7,16 Application of magnetic field strongly shifts the spin-reorientation transition, giving rise to 1% magnetodielectric effect. 16 Here, we present a detailed experimental study on the magnetodielectric and magnetoelastic coupling in TbFe 3 ͑BO 3 ͒ 4 .…”

Low-temperature absorption spectra and electron structure of HoFe3(BO3)4 single crystal

“…5), are easily identified at T = 2 K in the D 3 symmetry approximation (Table 2) basing on their polarizations, and they correspond to the total (9) decomposition. The Da and Db lines are, probably, the exciton-magnon ones (magnon in the Fe sublattice), at least the Db line, whose distance of 23.7 cm -1 from the D7 line is equivalent to 34 K. Indeed, a peak of the two-magnon Raman scattering was observed at approximately 52 cm -1 in some ferroborates [22]. The Da line can be also the consequence of the D2 line exchange splitting.…”

Spectroscopy ofRFe3(BO3)4multiferroics: phase transitions, spin-phonon interaction, coupled electron-phonon modes

“…High-resolution electronic spectra of EuFe3(BO3)4 allowed us to find that below TN iron magnetic moments order into a collinear structure along one of the C2 axes in the ab plane [6]. The temperature dependences of the phonon frequencies exhibit peculiarities at TN, which testifies the spin-phonon interaction [4,5,11]. Static and dynamic mechanisms of such interaction are discussed and an experimental proof of a role of the static mechanism is given [11].…”

“…All RE iron borates antiferromagnetically order at TN = 30 -40 K. Those of them that have an ionic radius of the R 3+ ion smaller than the one of Sm 3+ undergo a structural phase transition. We have shown that this is a so called "weak" first-order phase transition [4] and have discussed a possible nature of quasi-soft modes [5]. The temperature of the structural phase transition Ts and some of the optical properties turned out to depend on the crystal growth technology [6], which, from one hand, has to be taken into account when interpreting experimental data and, from the other hand, opens a possibility to control Ts.…”