Heat capacity and magnetocaloric effect in manganites (La1−yEuy)0.7Pb0.3MnO3 (y:0.2; 0.6)

Heat capacity and intensive magnetocaloric effect (MCE) in manganites (La_1−yEu_y)_0.7Pb_0.3MnO₃ [y=0.2; 0.6] (LEPM) were investigated by means of adiabatic calorimeter. The heat capacity anomaly as well as the values of both the intensive (ΔT_AD) and the extensive (ΔS_MCE) MCE were found to decrease upon increased replacement of La with nonmagnetic Eu. However, because of widening of the MCE peaks, the LEPM compounds show the relative cooling power, RCP/ΔH, comparable to other solid solutions of manganites. Owing to strong effect of Eu→La substitution on the Curie temperature, LEPM might have potential as the solid state refrigerants in multi-element cooling apparatus operating in a wide temperature range.     

Modulated magnetic structure in quasi-one-dimensional clinopyroxene NaFeGe<Subscript>2</Subscript>O<Subscript>6</Subscript>

The magnetic structure of the NaFeGe₂O₆ monoclinic compound has been experimentally investigated using the elastic scattering of neutrons. At a temperature of 1.6 K, an incommensurate magnetic structure has been observed in the form of an antiferromagnetic helix formed by a pairs of the spins of the Fe³⁺ ions with helical modulation in the ac plane of the crystal lattice. The wave vector of the magnetic structure has been determined and its temperature behavior has been studied. The analysis of the temperature dependences of the specific heat and susceptibility, as well as the isotherms of the field dependence of the magnetization, has revealed the existence of not only the order-disorder magnetic phase transition at the point T _N = 13 K, but also an additional magnetic phase transition at the point T _c = 11.5 K, which is assumingly an orientation phase transition.     

Fluorescence of a Liquid Drop with a Dye Excited by Femtosecond Laser Pulses

Results of investigations into the spectral and power characteristics of two-photon fluorescence of a liquid drop with the Rhodamine 6G dye irradiated by femtosecond laser pulses are presented. It is demonstrated that stimulated emission of two types is realized in drops with the concentrated dye solution, namely, superfluorescence within the drop volume and lasing on whispering gallery modes.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 15–19, April, 2005.     

Adiabatic calorimetric study of the intense magnetocaloric effect and the heat capacity of (La<Subscript>0.4</Subscript>Eu<Subscript>0.6</Subscript>)<Subscript>0.7</Subscript>Pb<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

The temperature dependences of the intense magnetocaloric effect ΔT _AD(T, H) and the heat capacity C _p (T) of the (La_0.4Eu_0.6)_0.7Pb_0.3MnO₃ manganite are directly measured using adiabatic calorimetry. The experimental dependences ΔT _AD(T) are in satisfactory agreement with those calculated from the data on the behavior of the magnetization. The factors responsible for the absence of an anomaly in the experimental temperature dependence of the heat capacity C _p (T) in the range of the magnetic phase transition are discussed.     

Specific Heat and Thermal Expansion of Triglycine Sulfate–Porous Glass Nanocomposites

The effect of restricted geometry on specific heat capacity and thermal expansion of the triglycine sulfate (TGS)–borosilicate glass composites have been studied first. A decrease in the entropy and temperature of the P2₁ ? P2₁/m phase transition in the TGS component with decreasing the glass matrix pore diameter at the invariable specific heat and thermal expansion coefficient has been observed. The estimates are indicative of the minor effect of internal pressure on the TGS pressure coefficient dT_C/dp in the composites.     

Effect of Isovalent Cation Substitution on the Thermal,Caloric, and Magnetocaloric Properties of the (La1 – yEuy)0.7Pb0.3MnO3 Manganites

Physics of the Solid State - Crystalline samples of the (La1&nbsp;–&nbsp;yEuy)0.7Pb0.3MnO3 (y = 0, 0.2, 0.4, 0.5, 0.6, and 0.8) manganite solid solutions have been grown. Temperature...     

A study of the effect of gradual substitution NH<Subscript>4</Subscript> → Cs on phase transitions in NH<Subscript>4</Subscript>LiSO<Subscript>4</Subscript> crystals

Solid solutions in the Cs_x(NH₄)_1?xLiSO₄ (0≤x≤0.35) system are grown and investigated. The birefringence (n_a?n_b) and the heat capacity are measured in the temperature range 100–530 K. The (x-T) phase diagram is constructed. It is demonstrated that the substitution of cesium for ammonium in the NH₄LiSO₄ crystal affects the transition temperatures in such a way that the region of the ferroelectric phase increases and the ferroelastic phase disappears at x>0.22. The character of the high-temperature transition remains unchanged (2β=0.24±0.01 for all compositions), but the birefringence anomaly and enthalpy decrease. As the concentration x increases, the low-temperature transition becomes more similar to a first-order transition: the birefringence jump δn and the temperature hysteresis ΔT increase.     

State of spin glass in SmFeTi<Subscript>2</Subscript>O<Subscript>7</Subscript>

The SmFeTi₂O₇ compound has been synthesized using the solid-phase reaction method. In order to determine the magnetic state, X-ray structural, Mössbauer, calorimetric, and magnetic measurements have been performed. The state of spin glass with the freezing point T _f = 7 K has been found for SmFeTi₂O₇.     

Structural,spectroscopic, and thermophysical investigations of the oxyfluorides CsZnMoO3F3 and CsMnMoO3F3 with the pyrochlore structure

The structure, infrared and Raman spectra, heat capacity, and thermal expansion have been investigated. It has been shown that, down to liquid-helium temperatures, the cubic pyrochlore structure of the CsMnMoO₃F₃ and CsZnMoO₃F₃ oxyfluorides remains stable. The influence of cation substitution on individual features of the properties of the oxyfluorides has been analyzed.     

Nature of optical properties of GdFe3(BO3)4 and GdFe2.1Ga0.9(BO3)4 crystals and other 3d5 antiferromagnets

Influence of the partial substitution of paramagnetic Fe³⁺ ions by diamagnetic Ga³⁺ ions in the trigonal crystal GdFe₃ (BO₃)₄ on its optical and magnetic properties is studied and discussed in connection with problems common for all antiferromagnets containing 3d ⁵ ions. Polarized optical absorption spectra and linear birefringence of GdFe₃ (BO₃)₄ and GdFe_2.1Ga_0.9 (BO₃)₄ single crystals have been measured in the temperature range 85–293 K. Specific heat temperature dependence (2–300 K) and structure of GdFe_2.1Ga_0.9 (BO₃)₄ crystal have been also studied. As a result of substitution of 30% Fe to Ga the Neel temperature diminishes from 38 till 16 K, the strong absorption band edge shifts on 860 cm^-1 (0.11 eV) to higher energy and the d-d transitions intensity decreases substantially larger than the Fe concentration does. Strong absorption band edge is shown to be due to Mott-Hubbard transitions. Correlation between position of the strong absorption band edge and the Neel temperature of antiferromagnets has been revealed. Properties of the doubly forbidden d-d transitions in the studied crystals and in other antiferromagnets are explained within the framework of the model of the exchange-vibronic pair absorption, which is theoretically analyzed in detail. The model permitted us to determine the connection between parameters of d-d absorption bands (intensity, width and their temperature dependences), on the one hand, and the exchange, spin-orbit and electron-lattice interactions, on the other hand.