Lattice vibrations of alpha'-NaV_2O_5 in the low-temperature phase. Magnetic bound states?

We report high resolution polarized infrared studies of the quarter-filled spin ladder compound alpha'-NaV_2O_5 as a function of temperature (5K <= T <= 300K). Numerous new modes were detected below the temperature T_c=34K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at T_c and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2, 1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.Comment: 15 pages, 13 Postscript figure

Effect of magnetic ordering of Dy

Optical transmission spectroscopy study of the Haldane magnet Dy2BaNiO5 was performed in the region of f-f transitions of the Dy3+ ion in a wide range of temperatures (5-300 К). At temperatures lower than TN (59 K), Kramers doublets of the rare-earth ion split. Spectroscopic data obtained were used to calculate the Schottky-type anomaly in the temperature dependence of the magnetic susceptibility of Dy2BaNiO5 and to model the experimental data available in literature. Anomalous behavior of crystal-field energies of the Dy3+ ion was attributed to the magnetoelectric interactions

Raman scattering on electronic levels in rare-earth iron borates

We have performed a Raman scattering study for single crystals of the rare-earth (RE) iron borates RFe3(BO3)4, R = Nd, Tb, Pr, in the range of temperatures 3-300 К. Electronic Raman scattering on the 4f levels of RE ions was registered, which enabled us to specify the schemes of crystal-field levels within ground multiplets of the RE ions. A splitting of the Kramers doublets in electronic Raman spectra of the neodymium iron borate testifies a magnetic ordering of the compound. Raman scattering from a coupled mode of the spin oscillations of the Fe and Nd subsystems was observed in NdFe3(BO3)4

Magnetic phase transitions in two-dimensional frustrated Cu

Using optical study of electronic spectra of rare-earth (RE) ions, magnetic phase transitions in the low-dimensional frustrated RE magnets Cu3R(SeO3)2O2Cl (R = Sm, Yb, Er, Nd, Pr, Eu) were investigated. Phase transitions were registered either by splittings of crystal-field (CF) doublets or by repulsion of CF levels of f-ions in a staggered magnetic field. Different scenarios of magnetic order in isostructural compounds of the francisite family are discussed

Raman scattering on electronic levels in rare-earth iron borates RFe3(BO3)4

We have performed a Raman scattering study for single crystals of the rare-earth (RE) iron borates RFe3(BO3)4, R = Nd, Tb, Pr, in the range of temperatures 3-300 К. Electronic Raman scattering on the 4f levels of RE ions was registered, which enabled us to specify the schemes of crystal-field levels within ground multiplets of the RE ions. A splitting of the Kramers doublets in electronic Raman spectra of the neodymium iron borate testifies a magnetic ordering of the compound. Raman scattering from a coupled mode of the spin oscillations of the Fe and Nd subsystems was observed in NdFe3(BO3)4

Study of wide band-gap crystal LiCaAlF

Polarized IR-reflection spectra and results of ab initio calculations of vibrational and electronic properties of LiCaAlF6 single crystal are presented. It is shown that the crystal band gap is direct. Experimental and theoretical parameters are obtained for dipole-active and all phonons, respectively, including silent modes. Experimental IR-reflection and Raman spectra are well described in the frame of results obtained by ab initio calculations. The peculiarities are discussed concerning the structure of electronic bands, the interatomic interactions, the character of lattice vibrations, and the phonon dispersion

Magnetic phase transitions in two-dimensional frustrated Cu 3

Using optical study of electronic spectra of rare-earth (RE) ions, magnetic phase transitions in the low-dimensional frustrated RE magnets Cu3R(SeO3)2O2Cl (R = Sm, Yb, Er, Nd, Pr, Eu) were investigated. Phase transitions were registered either by splittings of crystal-field (CF) doublets or by repulsion of CF levels of f-ions in a staggered magnetic field. Different scenarios of magnetic order in isostructural compounds of the francisite family are discussed