V. A. Bedarev

IR active vibrations of a TbFe3(BO3)4 crystal

The IR reflection spectra of a TbFe3(BO3)4 crystal are measured in the spectral range 200–2000cm−1 in E⊥c polarization at temperatures 10 and 300K. The reflection spectrum so obtained is analyzed and its interpretation is given on the basis of the internal vibrations of the ionic complexes BO33−, FeO69−, and TbO69− of the TbFe3(BO3)4 crystal. Davydov splitting on the internal vibrational modes at a structural phase transition, which is accompanied by multiplication of the unit cell, was not observed in the experimental spectral range. This is due to the localization of the vibrations of the ionic complexes BO33−, FeO69−, and TbO69− of the TbFe3(BO3)4 crystal.

Rotational magnetocaloric effect in TbAl3(BO3)4

A rotational magnetocaloric effect is predicted in the TbAl3(BO3)4 crystal based on the results of measuring field dependences of magnetization and the temperature dependence of heat capacity. The effect is modeled using the quasi-doublet approximation. Changes to the crystal entropy at constant temperature are determined, as well as at varying temperature under adiabatic conditions. The refrigerant capacity of the crystal is estimated. It is shown that terbium aluminum borate is a promising material for magnetic cooling.

Low-temperature magnetic phase transition in aluminum borate TbAl3(BO3)4

Magnetic ordering temperature, initial splitting and effective g-factor of the ground quasi-doublet of a Tb3+ ion were determined by investigating the heat capacity and ESR in a TbAl3(BO3)4 single crystal. The parameters of the magnetic interaction were calculated.

Structural phase transition in two-dimensional tetramer-cuprate Na5RbCu4(AsO4)4Cl2

Raman scattering and optical birefringence are used in to investigate a low-temperature phase transition in a single crystal of the two-dimensional Na5RbCu4(AsO4)4Cl2. Phonon anomalies point to a first-order nature of the transition. The observed transition is most probably related to an order-disorder transition of the Rb ion positions along the z axis within the ionic framework of mixed alkali metal chloride lattices.

Magnetoresonance properties of antiferromagnetic TbFe3(BO3)4 at low temperatures

The magnetic resonance and field dependence of magnetization were studied in a single crystal of TbFe3(BO3)4 at temperatures from 2 to 13 K and frequencies from 18 to 142 GHz. Two pairs of lines with different intensities were found in the EPR spectrum. The found lines can be assigned to two types of centers: the Tb3+ ions which neighbor with the Bi and Mo growth impurities. The initial splitting of the lowest quasi-doublet of such Tb3+ ions by the crystal field and exchange field acting on the rare-earth ions from the iron sublattices were determined. The amount of these centers was estimated.

Light-induced optical absorption in the garnet Ca3Mn2Ge3O12

Light-induced change in the optical absorption of the garnet Ca3Mn2Ge3O12 has been found. The magnitude of the light-induced optical absorption does not depend on the polarization state of the exciting illumination. The effect persists for a long time at low temperatures and can be attributed to light-induced generation or redistribution of Mn4+ ions in the crystal.

Magnetic field-induced rotation of the plane of polarization of light in the antiferromagnetic ferroborate TbFe3(BO3)4

The magnetic field dependences of the rotation of the plane of polarization of light and the magnetization in single crystals of the ferroborate TbFe3(BO3)4 are studied. The main contribution to the magnetic field-induced rotation of the plane of polarization is found to be from the magnetic subsystem of the terbium ions.

Effect of light illumination on antiferromagnet-metamagnet phase transitions in the garnet Ca3Mn2Ge3O12

The effect of linearly polarized light illumination on the metamagnetic phase transition in the antiferromagnetic garnet Ca3Mn2Ga3O12 is studied. The crystal is exposed to light propagating both along the tetragonal axis [001] and along the [100] direction. In both cases, a change of the field Ht of the metamagnetic phase transition is observed under illumination, and this change depends on the orientation of plane or polarization of the light with respect to the crystal axes. In the first case, k‖H‖[001], the value of Ht decreases on exposure to light with the polarization E‖[110] and increases on exposure to light with the polarization E‖[110]. In the second case, k‖H‖[100], the value of Ht decreases irrespective of the orientation of the plane of polarization of the light with respect to the crystal axes. However, the magnitudes of the change of Ht are different for light with the polarization E‖[011] and with the polarization E‖[011]. The change of the field of the metamagnetic phase transition in t...

Antiferromagnetic resonance in crystalline PrFe3(BO3)4

Experimental AFMR studies of crystalline PrFe3(BO3)4 over a wide frequency range of 10–143 GHz at a temperature of 4.2 K have been carried out. The high-frequency properties of praseodymium ferroborate are well described in terms of a model of a two-sublattice antiferromagnet with an “easy axis” anisotropy. An energy gap of 134.3 ± 0.5 GHz is determined and the magnitude of the effective magnetic anisotropy field is estimated to be 1.9 ± 0.1 kOe. An analysis indicates that the spin-orientational phase transition in this compound is a first order transition.

Features of electronic paramagnetic resonance in the ErAl3(BO3)4 single crystal

An additional resonance line was found in the EPR spectrum of the ErAl3(BO3)4 crystal at a temperature of 4.2 K, along with the main line. The appearance of an additional line is associated with the possible formation of magnetic clusters in the crystal.