The interrelation of magnetic and dielectric properties of Co(x)Mn(1 - x)S solid solutions.

Magnetization of the cation-substituted Co(x)Mn(1 - x)S sulfides upon cooling in zero and 100 Oe magnetic fields at the temperatures 4-300 K has been measured. Permittivity of these materials at frequencies from 1 to 100 kHz in magnetic and dc electric fields in the 100-300 K temperature range has been determined. Change in the dielectric permittivity under an external magnetic field is found to have a maximum in the temperature ranges of T1 ~ (110-120 K) and T2 ~ (230-250 K). Formation of spontaneous magnetic moment and the rise of magnetic susceptibility are revealed at the same temperatures in the Co(x)Mn(1- x)S solid solutions. Features of the magnetoelectric properties of the sulfides have been explained by orbital ordering.

Dielectric properties of a mixed-valence Pb3Mn7O15 manganese oxide.

We investigated the low-frequency dielectric properties of a Pb(3)Mn(7)O(15) single crystal with manganese ions in the mixed-valence state (Mn(3+)/Mn(4+)). Dielectric relaxation was found in the frequency window from 20 to 100 kHz in the temperature range 110-180 K. The dielectric spectra of the crystal were analyzed using a Debye model. Estimations made within the model and analysis of resistivity data suggest that the relaxation behavior of the dielectric constant is related to polaronic charge carrier hopping. Around 250 K, charge ordering occurs in the crystal when the Mn(3+) and Mn(4+) ions are arranged in a specific order among the crystal sites. With a decrease in temperature, an ac electric field can induce a charge hop between the equivalent lattice sites available, related to crystal symmetry. This hopping is equivalent to the reorientation of an electric dipole that yields Debye-type behavior of the complex dielectric constant. The observed anisotropy in the behavior of the dielectric properties and resistivity can be attributed to a pronounced two-dimensional character of the crystal structure.

Low-temperature magnetic phase diagram of HoFe(3)(BO(3))(4) holmium ferroborate: a magnetic and heat capacity study.

We present the results of the magnetic and heat capacity study of a magnetic phase diagram of a HoFe(3)(BO(3))(4) single crystal. Two magnetic phase transitions are found in the low-temperature region. The transition from the paramagnetic to easy-plane antiferromagnetic state occurs at T(N) = 37.4 K and is independent of an applied magnetic field. The sharp heat capacity peaks and magnetization jumps corresponding to the spontaneous and field-induced spin-reorientation transitions between the easy-axis and easy-plane states are observed below 4.7 K. Also, the additional heat capacity peaks, which can be attributed to the Schottky anomalies with the field-dependent characteristic temperatures, are found. According to the magnetic and thermal measurement data, the magnetic phase diagrams of HoFe(3)(BO(3))(4) for the magnetic field parallel and perpendicular to the crystal axis are constructed.

[Interpretation of mechanical impedance of biological tissues in the three level model with the power source of vibrations]. / Interpretatsiia mekhanicheskogo impedansa biologicheskikh tkanei v trekhsloinoi modeli s silovym istochnikom kolebanii.

Theoretical expressions were derived for the mechanical impedance of a round piston on the surface of a viscoelastic triple layer with sublayers linked with each other and with the rigid base. The expressions were obtained on the assumption that the piston creates an even oscillatory pressure and does not create shear stresses. The calculations in the developed model were compared with corresponding calculations in the known strict model and with experimental values obtained on a relaxed and stressed human biceps. The results obtained suggest that models of this kind can be used for reconstructing the mechanical parameters of multilayer biological tissues.