Electromechanical properties of Pb<Subscript>3</Subscript>Ga<Subscript>2</Subscript>Ge<Subscript>4</Subscript>O<Subscript>14</Subscript> piezoelectric crystals grown from solution in a melt

Single crystals of lead gallium germanate Pb₃Ga₂Ge₄O₁₄ are grown from their own solution melts. The propagation of bulk acoustic waves is investigated, and the elastic, piezoelectric, and dielectric constants are calculated. The temperature dependences of the dielectric constants of this compound are analyzed.     

Intramolecular cyclization of 5-aryl-3-arylamino-4-benzoyl-1h-3-pyrrolin-2-ones to pyrrolo[3,4-<Emphasis Type="Italic">b</Emphasis>]quinolines

It has been shown that 5-aryl-3-arylamino-4-benzoyl-1H-3-pyrrolin-2-ones cyclize in the presence of conc. H₂SO₄ to give pyrrolo[3,4-b]quinolines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1543–1545, October, 2004.     

Magnetic and thermal properties of single-crystal NdFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The neodymium ferroborate NdFe₃(BO₃)₄ undergoes an antiferromagnetic transition at T _N = 30 K, which manifests itself as a λ-type anomaly in the temperature dependence of the specific heat C and as inflection points in the temperature dependences of the magnetic susceptibility χ measured at various directions of an applied magnetic field with respect to the crystallographic axes of the sample. Magnetic ordering occurs only in the subsystem of Fe³⁺ ions, whereas the subsystem of Nd³⁺ ions remains polarized by the magnetic field of the iron subsystem. A change in the population of the levels of the ground Kramers doublet of neodymium ions manifests itself as Schottky-type anomalies in the C(T) and χ(T) dependences at low temperatures. At low temperatures, the magnetic properties of single-crystal NdFe₃(BO₃)₄ are substantially anisotropic, which is determined by the anisotropic contribution of the rare-earth subsystem to the magnetization. The experimental data obtained are used to propose a model for the magnetic structure of NdFe₃(BO₃)₄.     

Spectroscopic study of magnetic phase transitions in Nd<Subscript>x</Subscript>Gd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Magnetic ordering and spin reorientation in iron borates Nd_xGd_1?xFe₃(BO₃)₄ (x = 0.01, 0.04, 0.25, 1.0) are studied using a rare-earth spectroscopic probe.     

Magnetization and specific heat of DyFe3(BO3)4 single crystal

We present thermodynamic and magnetic studies of single crystalline DyFe₃(BO₃)₄. The data indicate an easy axis antiferromagnetic order below T_N~ 38 K which we attribute to the Fe subsystem. The Dy subsystem remains paramagnetic down to the lowest investigated temperatures of 2 K, but it is polarized by the Fe spins due to a f-d interaction. External magnetic field leads to a spin-flop transition in the iron subsystem as well as to superposed magnetization in the Dy subsystem. The repopulation of two low-lying Kramers doublets in Dy³⁺ ions results in well defined Schottky anomalies in specific heat and magnetization.     

Colossal magnetodielectric effect in SmFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> multiferroic

The colossal (more than threefold) decrease in the dielectric constant ɛ in the easy-plane SmFe₃(BO₃)₄ ferroborate in a magnetic field of ∼5 kOe applied in the basal ab plane of the crystal has been found. A close relation of this effect to anomalies in the field dependence of the electric polarization has been established. It has been shown that this magnetodielectric effect is due to the contribution to ɛ from the electric susceptibility, which is related to the rotation of spins in the ab plane, arises in the region of the antiferromagnetic ordering T < T _N = 33 K, and is suppressed by the magnetic field. A theoretical model describing the main features of the behavior of ɛ and electric polarization in the magnetic field has been proposed, taking into account the additional anisotropy in the basal plane induced by the magnetoelastic stresses.     

Magnetoelectric interactions in rare-earth ferroborates

Magnetic-field-induced phase transitions in single crystals of the rare-earth ferroborates GdFe₃(BO₃)₄ and NdFe₃(BO₃)₄ have been studied by measuring magnetoelectric dependences and torque curves. These phase transitions can serve as one of the possible mechanisms for magnetic control of electric polarization. Magnetic phase transitions in GdFe₃(BO₃)₄ are analyzed theoretically.     

Magnetostriction studies of magnetic phase transitions in the copper metaborate CuB2O4

The field dependences of the longitudinal and transversal magnetostriction of the copper metaborate CuB₂O₄ were measured at various temperatures below the Néel point in magnetic fields directed along the tetragonal axis or in the basal plane. Magnetostriction was found to exhibit jumps at magnetic-field-induced phase transitions to a commensurate weak ferromagnetic state, as well as to grow smoothly in fields above and below the critical level. The magnetostriction observed in a magnetic field directed along the tetragonal axis is shown to be primarily caused by volume dilatation of the crystal. The experimental data obtained were used to construct the magnetic phase diagram of copper metaborate magnetized along the tetragonal axis.     

On the excitation and propagation of magnetoelastic and magnetostatic waves in inhomogeneously magnetized monocrystals

Results are presented of the experimental study of the excitation of magnetoelastic and magnetostatic waves in monocrystalline prisms of iron garnets magnetized by an inhomogeneous external field with a longitudinal component decaying in the axial direction. Application of such excitation conditions to the reduction of the working frequencies of controllable microwave delay lines is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 53–56, September, 1981.     

Evolution of the mössbauer spectra of ludwigite Co3 − x Fe x O2BO3 with substitution of iron for cobalt

A concentration series of single crystals of iron-cobalt ludwigites Co_{3 ? x} Fe _x O₂BO₃ (x = 0.0125, 0.025, 0.050, 0.10, 1.0) has been synthesized. The structure has been studied using X-ray diffraction and Mössbauer effect. A preferred occupation of nonequivalent crystallographic positions by iron in the ludwigite structure has been revealed. It has been found that the valence of substituting iron ions is three. It has been revealed that the structure of the γ-resonance spectrum of Co₂FeO₂BO₃ is complicated due to a composition disorder in the system.