Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds

The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field.     

Low field magnetocaloric effect and heat capacity of A-site ordered NdBaMn2O6 manganite

The magnetocaloric effect (MCE) in the A-site ordered manganite NdBaMn₂O₆ is studied. The MCE in this compound has an anomalous behavior. In low magnetic fields, the abrupt transitions between the direct and inverse magnetocaloric effects are observed. In a relatively strong magnetic field , the direct and inverse effects are observed only at cooling, while the heating mode reveals only an inverse MCE. The value of the MCE ( and for  kOe) does not reach high values, but the proximity of the effects occurring at room temperatures expects the use of both effects in the magnetic cooling technology.     

Magnetocaloric properties of La0.7Ca0.3MnO3 manganites with 16O → 18O isotopic substitution

This paper reports on a study of the effect of isotopic ¹⁶O → ¹⁸O oxygen substitution on the heat capacity and magnetocaloric properties of the La_0.7Ca_0.3MnO₃ manganite. Direct measurements of the magnetocaloric effect have demonstrated that, in La_0.7Ca_0.3MnO₃, the effect reaches a fairly large magnitude, but its temperature width is rather small. The ¹⁶O ar ¹⁸O isotopic substitution shifts the temperature of the maximum of the effect toward lower temperatures while leaving its magnitude practically unchanged. The magnetocaloric effect in the La_0.7Ca_0.3Mn¹⁶O₃ + La_0.7Ca_0.3Mn¹⁸O₃ sandwich structure has been measured by the direct method. It has been shown that fabrication of a sandwich from materials with close temperatures of the maxima of the magnetocaloric effect permits increasing the relative cooling power (RCP) compared with that of the starting materials.     

Magnetocaloric properties of manganites in alternating magnetic fields

The magnetocaloric effect has been measured in manganites of various chemical compositions in weak alternating magnetic fields. The capabilities of a simple method for measuring the magnetocaloric effect by modulating the magnetic field have been demonstrated. The dependence of the magnetocaloric effect on the temperature, magnetic field, and chemical composition of samples is interpreted.