On the correlation between anisotropy of gyrotropic and magnetic properties of samarium and terbium orthoferrites

Rare earth orthoferrites are interesting for investigation and promising materials for practical application. This paper deals with the existence of the correlation between the polar diagrams of polarization plane rotation obtained by us (SIROTA, LOMAKO 1976, 1978, 1979) and those of magnetic torques plotted from the data of BELOV et al. 1967, 1968a, 1968b). In this case the relationship is established between the optical anisotropy and crystallographic magnetic anisotropy of the orthoferrites crystals under investigation.     

SEM diagnostics of the surface of MK-40 and MA-40 heterogeneous ion-exchange membranes in the swollen state after thermal treatment

The morphology of the surface of MK-40 and MA-40 ion-exchange membranes in the swollen state after chemical and thermal treatment is studied using scanning electron microscopy. The distribution of portions of the ion exchanger on the surface of heterogeneous membranes is found to be of a complex stochastic nature; their sizes for the MK-40 and MA-40 membranes are 5–30 and 8–40 μm, respectively, while the sizes typical for the secondary porous structure are 2–8 μm. An increase in the share of the ion-exchange component of the surface (by 20–40%), the sizes of the ion-exchange portions (by 20%), and the surface porosity (by two-three times) in the samples subjected to thermal treatment is revealed.     

A new surface phase in liquid normal-alkanes

A new surface phase is found in liquid normal-alkanes. X-ray and surface tension measurements show the formation of a crystalline monolayer on the surface of the liquid at temperatures up to 3°C above the bulk solidification temperature, T_f. The molecules in the monolayer are hexagonally packed and oriented normal to the surface. A single solid monolayer persists down to T_f, thus exhibiting a very limited partial wetting. The new surface phase is obtained only for chain lengths 14<n50. Its vanishing for n14 is interpreted as a possible transition from surface freezing to surface melting behaviour. The measurements are satisfactory accounted for within a simple theory based on surface energy cosiderations.     

Cohesive energy, phonon spectra, and thermodynamic properties of elements with the structures A1, A2, A3, A4—Al, Cu, V, Ti, Mg, Si, and Sn

The dependences of the cohesive (atomization) energy on the interatomic distance for elements Al, Cu, Ti(A₂), V, Mg, Ti(A₃), Si, and Sn are calculated using methods based on the Thomas-Fermi-Dirac-Gambosh statistical atomic theory. The obtained dependences are approximated by the Mie-Grüneisen potential. The phonon spectra calculated on the basis of the Born-Kärmän model and the Born-Kärmän-Blackman-de Lunay approach are used to determine the temperature dependences of the specific heat, free energy, and internal energy of the elements under investigation. The calculated cohesive energy, equilibrium interatomic distances, and temperature dependences of the specific heat agree with the experimental data.     

Crystallo-optical properties of the SmxTb1−xFeO3 orthoferrites

The paper reports the results of X-ray diffraction studies as well as the angular dependences of rotation of the plane of polarization and birefringes of the Sm_xTb_1−xFeO₃ crystals (x = 0; 0.2; 0.4; 0.55; 0.8; 1). The polar diagrams presented for the plane (001) have the symmetry mm2, while for (110), the symmetry lowers up to the axis of a second order. The gyrotropic measurements made have allowed us to refer the Sm_xTb_1−xFeO₃ to a planar class of an orthorhombic crystal system with the space group C_2v⁹–Pn2a, class mm2. – The magnitude of birefringence for the Sm_xTb_1−xFeO₃ is found to be sensitive both to a crystallographic direction and a composition, the greatest values stand for (110). For (001), a non-monotonous birefringence variation with the composition is observed. The angles between optic axes, calculated by the birefringence magnitudes, are in fair agreement with gyrotropic data for the compositions x = 0.55 – 1.