Inelastic light scattering spectra of several members of the ${\mathrm{RFe}}_3({\mathrm{BO}}_3{)}_4$ 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 compounds, and a subsequent spin-reorientational transition for ${\mathrm{GdFe}}_3({\mathrm{BO}}_3{)}_4$. 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.

Optical absorption spectra of the ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ single crystals and luminescence spectra of the ${\mathrm{Y}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7:\mathrm{Yb}$ (1%) polycrystalline samples were registered at temperatures $4.2–300\mathrm{K}$. These spectra and earlier published data on magnetic properties of ${\mathrm{Yb}}^{3+}$ ions and on the temperature dependence of the electric field gradient at Yb nuclei in ${\mathrm{Yb}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ were used to analyze the crystal-field parameters in rare-earth titanates with the pyrochlore structure. The self-consistent sets of crystal-field parameters for rare-earth ions in the $16d$ sites with the $D_{3d}$ symmetry that describe satisfactory all known single-ion magnetic properties and low-energy excitations in $R_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ crystals ($R=\mathrm{Tb}$, Ho, Er, Tm, Yb) are presented.

Cascade of phase transitions in GdFe3(BO3)4 at 156, 37, and 9 K has been detected by specific heat measurements and further studied by Raman scattering and Nd3+spectroscopic probe method. A weakly...

We report temperature-dependent x-ray powder diffraction patterns and single-crystal electron spin resonance (ESR) and Raman spectra of the two-dimensional triangular-lattice antiferromagnet $\mathrm{RbFe}({\mathrm{MoO}}_4{)}_2.$ A structural phase transition is found to occur in this compound at $T_c\simeq 190\mathrm{K}.$ By analyzing our data and the literature data on similar compounds, we conclude that the 190 K transition comprises rotations of ${\mathrm{MoO}}_4$ tetrahedra and is, most likely, a transformation from a highly symmetric $P3\mathrm{}¯m1\mathrm{}$ room-temperature structure into a very similar but less symmetric $P3\mathrm{}¯c1\mathrm{}$ low-temperature one. The shift of the ESR frequency and the ESR linewidth were found to be determined by the crystal field influence and are described well considering the single-ion anisotropy with the constant ${D/k}_B=0.25\mathrm{}\mathrm{K}.$ The change of the crystal field at the iron site below the phase-transition point $T_c$ is estimated.