[en] A systematic investigation of the structure and magnetic properties of arc-melted and as-quenched Sm₂Fe_17-xGa_xC_1.5 samples with 0≤x≤6 has been made by X-ray diffraction and magnetic measurements. X-ray diffraction studies have shown that these samples crystallize in the rhombohedral Th₂Zn₁₇-type structure. The unit-cell volumes v of Sm₂Fe_17-xGa_xC_1.5 compounds increase monotonically with increasing Ga concentration. The Ga-concentration dependence of the Curie temperature T_C exhibits a maximum value of 633 K at about x=2. The room-temperature saturation magnetization M_s decreases monotonically with increasing Ga concentration. The Sm₂Fe_17-xGa_xC_1.5 compounds exhibit an easy c-axis anisotropy at room temperature. The anisotropy field is found first to increase and then to decrease with increasing x, having a maximum value of 130 kOe at about x=2. The coercivities of 13.0-16.0 kOe are obtained in as-quenched Sm₂Fe_17-xGa_xC_1.5 (x=2 and 3) ribbons prepared at the speeds of 15-30 m/s at room temperature. The substitution of Ga in Sm₂Fe₁₇C_1.5 not only stabilizes the hard magnetic phase but also leads to the increase in coercivity. (orig.)

[en] The structural and magnetic properties of compounds in the series Sm₂(Fe_1-xCo_x)₁₆SiC are investigated by means of X-ray diffraction (XRD) and magnetization measurements. Samples with x = 0 to 0.3 are prepared by the arc-melting method. XRD patterns indicate that arc-melted Sm₂(Fe_1-xCo_x)₁₆SiC alloys crystallize in the rhombohedral Th₂Zn₁₇-type structure. The substitution of Co leads to a decrease in the lattice constants and the unit-cell volume. The Curie temperature increases monotonically with increasing Co concentration from 576 K for x = 0 to 796 K for x = 0.3. The saturation magnetization is higher than 125 emu/g for Sm₂(Fe_1-xCo_x)₁₆SiC with x > 0. Sm₂(Fe_1-xCo_x)₁₆SiC with x ≤ 0.3 compounds exhibit an easy c-axis anisotropy at room temperature and the anisotropy field H_a is found to have a maximum value of 120 kOe for x = 0.1. (orig.)

[en] Based on the statistical theory of X-ray dynamical diffraction for thin films, the mosaicity of three types of semiconductor epitaxic layers has been investigated by analyzing their rocking curves by the X-ray double-crystal diffraction method. It is shown that the statistical theory can provide quantitative information on the mosaicity of the epitaxic layers such as the mean size and the mean disorientation of mosaic blocks in the layers. Some misunderstandings in interpreting experimental data are cleared up by taking into account the effect of diffuse scattering. It is emphasized that attempts to obtain structural parameters of specimens from their rocking curves by means of the Takagi-Taupin equations for coherent fields only are not strictly correct since diffuse scattering causes additional changes in the tails of the rocking curves. (orig.)

[en] A one-dimensional solvable model of fermions is mapped to the XXX ferromagnetic chain. At T=0, it is shown that there is off-diagonal long range order for the reduced density matrix rho₂ in the model. In the momentum space the single particle state pairs are coherently occupied. The momenta of the particles in each pair are equal but with opposite directions

[en] Short communication

[en] Er₂Fe₁₅Ga₂C_x compounds with x = 0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 are prepared by arc melting and heat treating at 1400 K for two days. X-ray diffraction of Er₂Fe₁₅Ga₂C_x shows that the prepared samples are approximately single phase, having the hexagonal Th₂Ni₁₇-type or the rhombohedral Th₂Zn₁₇-type structure. For x ≥ 2.5, the samples contain a few percent of α-Fe. Both substitutional gallium and interstitial carbon in Er₂Fe₁₇ lead to an increase of the unit cell volume. The Curie temperature is found to rise with x from 478 K for x = 0 to 611 K for x = 2.5, and decreases to 585 K at x = 3.0. The saturation magnetization μ_s at 1.5 K is almost independent of carbon concentration. The thermomagnetic measurements demonstrate that all samples studied here exhibit a spin reorientation transition. The spin reorientation temperature is found to increase strongly with the carbon concentration for x < 1.5, and it is essentially constant at about 230 K for x ≥ 1.5. (orig.)

[en] The LaFe_12-xAl_xMn (x=2,3,4,5,6,7) alloys have been annealed at different temperatures and for different periods. The crystal structures and magnetic properties of these compounds are investigated by X-ray diffraction and ac susceptibility measurements. The results indicate that the NaZn₁₃-type structure is slightly sensitive to Mn-doping. However, the magnetic properties of these compounds are strongly related to the annealing temperature and period. A structural transition occurs in LaFe₅Al₇Mn after annealing at 773 K for about three months. A magnetic transition from ferromagnetic to paramagnetic state is found in LaFe₇Al₅Mn after annealing at 773 K for two months. (orig.)

[en] The crystal structure and magnetic properties of LaCo_13-xAl_x compounds have been investigated by X-ray powder diffraction and magnetization measurement. X-ray powder diffraction shows that the compounds crystallize in cubic NaZn₁₃-type structure with lattice parameter a = 11.345(2) to 11.473(4) A in the range of x ≤ 2.7, and in the tetragonal Ce₂Ni₁₇Si₉ structure at x = 3. Magnetization measurements reveal that both cubic and tetragonal LaCo_13-xAl_x are ferromagnetic with Curie temperature higher than 840 K, and the magnetic moment per Co atom in LaCo_13-xAl_x compounds decreases with Al content. (orig.)

[en] We put forward a conjecture for a class of scalar field theories analogous to the recently proposed weak gravity conjecture for U(1) gauge field theories. Taking gravity into account, we find an upper bound on the gravity interaction strength, expressed in terms of scalar coupling parameters. This conjecture is supported by some two-dimensional models and noncommutative field theories

[en] The quantum version of the direct and inverse problem of the inverse scattering transform for the nonlinear Schroedinger model of spin-1/2 particles with attractive coupling are investigated. The Yang-Baxter equations are solved to get various commutation relations; the energy spectrum and the quantum Gelfand-levitan equations are obtained. (orig.)