Magnetic and dielectric studies of multiferroic CuO nanoparticles confined to porous glass

Dc magnetization and ac electric permittivity were measured for the CuO-porous glass nanocomposite made and for pressed powder CuO. Magnetization curves showed a bend between two linear segments for both the nanocomposite and bulk cupric oxide at 230 K evidencing that the temperature of the transition from the paramagnetic into multiferroic phase did not change noticeably under nanoconfinement. Results suggested also a reduction of the temperature of the second transition into the collinear antiferromagnetic phase. ZFC and FC magnetizations were found to bifurcate for the nanocomposite and bulk CuO. The bifurcation was accompanied with peaks on ZFC magnetization.     

Acoustic studies of melting and crystallization of sodium nitrite nanocrystals in the pores of mesoporous silicate matrices

A conventional phase-pulse acoustic method was used to study melting and crystallization of sodium nitrite embedded in the pores of mesoporous silicate matrices. The pore diameter was 20, 37, and 52 Å. The measurements were performed at a frequency of 3–8 MHz in the temperature interval 290–560 K. The temperature dependence of ultrasonic velocity was found to exhibit anomalies corresponding to phase transitions of sodium nitrite. The transitions were smeared in temperature and shifted to lower temperatures from the melting point T _b of bulk sodium nitrite; the shift in crystallization temperature was greater than that of the melting temperature. The irreversible character of melting was revealed. The size dependence of the melting temperature of sodium nitrite was obtained. Phenomena observed in the experiments were discussed with the use of different size effect models.     

Inhomogeneous configurations in the Lifshitz-type improper incommensurate ferroelectric thin films

The model with the Lifshitz invariant for periodic and helicoidal structures has been analyzed without neglecting of the amplitude function oscillations considering the amplitude and phase functions as equal in significance variables. We have shown that this approach gives significantly richer picture of the order parameter phase and amplitude distribution, than in the approximation of the constant amplitude. The amplitude function oscillations are shown to be extremely important for finding of the phase function distribution in a thin film. Along with numerical calculations, analytic consideration is carried out in the limit of small anisotropy. Both regular and chaotic regimes are studied.     

Dielectric studies of a α-LiIO<Subscript>3</Subscript> crystals grown from neutral and alkaline solutions

The dielectric properties of lithium iodate crystals of the hexagonal modification grown from solutions with pH = 6.2, 7.1, and 11.0 in the frequency range from 25 Hz to 1 MHz at temperatures of 290–420 K were investigated. The temperature dependence of the imaginary part of the permittivity was found to exhibit clearly pronounced relaxation peaks originating from ionic mobility. The shift in the position of the relaxation maxima was used to calculate the activation energy and attempt frequency for mobile ions. The Cole-Cole diagrams revealed the existence of a spectrum of relaxation times. The presence of the specific feature in the ionic mobility of lithium iodate crystals grown from solutions with pH ～ 7 was confirmed.     

NMR Investigation of the WTe2 Weyl Semimetal below the Topological Transition Temperature

Physics of the Solid State - NMR investigations are performed on 125Te nuclei of WTe2 Weyl topological semimetal at temperatures of 41 and 293 K. The measurements were carried out using a Bruker...     

Temperature dependence of the spin-lattice relaxation time for quadrupole nuclei under conditions of NMR line saturation

The contributions of different mechanisms of nuclear spin-lattice relaxation are experimentally separated for ⁶⁹Ga and ⁷¹Ga nuclei in GaAs crystals (nominally pure and doped with copper and chromium), ²³Na nuclei in a nominally pure NaCl crystal, and ²⁷Al nuclei in nominally pure and lightly chromium-doped Al₂O₃ crystals in the temperature range 80–300 K. The contribution of impurities to spin-lattice relaxation is separated under the condition of additional stationary saturation of the nuclear magnetic resonance (NMR) line in magnetic and electric resonance fields. It is demonstrated that, upon suppression of the impurity mechanism of spin-lattice relaxation, the temperature dependence of the spin-lattice relaxation time T₁ for GaAs and NaCl crystals is described within the model of two-phonon Raman processes in the Debye approximation, whereas the temperature dependence of T₁ for corundum crystals deviates from the theoretical curve for relaxation due to the spin-phonon interaction.     

Dielectric parameters of mesoporous sieves filled with NaNO<Subscript>2</Subscript>

This paper reports on a dielectric study of MCM-41 molecular sieves with cellular channels of different sizes filled with the NaNO₂ ferroelectric. The temperature dependences of the permittivity and electrical conductivity of sodium nitrite in cellular channels are calculated from experimental data on the permittivity and electrical conductivity of the composite. The calculations are performed using the relationships obtained for the hexagonal matrix with parallel cylindrical inclusions within pores. The observed increase in the conductivity of sodium nitrite in confined geometry at high temperatures is attributed to partial melting. It is shown that the increase in the permittivity of the composite is caused by Maxwell-Wagner relaxation processes.     

Phonon Spectroscopy of the Schottky-Like Low-Energy Paramagnetic Excitations in Garnet Solid Solution Crystals

Journal of Experimental and Theoretical Physics - The interaction of weakly nonequilibrium phonons with the low-energy paramagnetic excitations of the rare-earth ions of the yttrium series in...     

Dielectric properties of crystalline binary KNO3—AgNO3 mixtures embedded in nanoporous silicate matrices

The results of dielectric studies of MCM-41 sili cate matrices with cellular pores (37.0 and 26.1 ? in diameter) filled by binary mixtures of K_1−x Ag _x NO₃ (x=0, 0.05, 0.10) are reported in comparison with those obtained for bulk salts of the same composition in the temperature range of structural phase transitions. It has been revealed that, upon heating, the nanocomposites undergo transitions from crystal modification II to phase I, as in bulk KNO₃, whereas the bulk mixtures with x=0.05 and 0.10 have a complex structure in accordance with the phase diagram. It has been shown that embedding binary salts and pure potassium nitrate in pores with a diameter of 26.1? results in the formation of an intermediate ferroelectric phase upon cooling. The permittivity and electrical conductivity are found to increase with increasing AgNO₃ concentration in bulk samples, as well as with decreasing pore size in the nanocomposites for all values of x.