S. A. Lachenkov

Effect of the magnetic subsystem of the DyRh3.8Ru0.2B4 compound on its superconducting properties

A new DyRh3.8Ru0.2B4 magnetic superconductor with LuRu4B4-type structure is synthesized and studied. The magnetic subsystem of the compound is shown to substantially affect the superconducting sub-system. The field dependence of the magnetic moment M(B) of the complex DyRh3.8Ru0.2B4 rhodium boride differs markedly from that of the nonmagnetic classic YRh4B4 superconductor. The Bc2(T) dependence for the magnetic DyRh3.8Ru0.2B4 superconductor deviates from the classic parabolic function and exhibits an abrupt rise at 2.8 K, which is related to the transition of the magnetic subsystem of the compound from a ferrimagnetic (FM) to antiferromagnetic (AFM) state. The FM AFM transition of the magnetic subsystem is accompanied by the transition of the superconducting subsystem to a thermodynamically more stable superconducting state.

A Giant Increase in the Electrical Conductivity of the High-Resistivity Film MoS2 Semiconductor under Continuous Proton Injection

The highly reproducible effect of a giant (10 000-fold) increase in the electrical conductivity of a film sample of a high-resistivity MoS2 semiconductor with a layered structure under continuous proton injection in dynamic equilibrium conditions is reported for the first time. The effect disappears when the process of proton injection is interrupted. The potential to control the composition and the properties of materials by doping them with charge carriers of different signs, masses, and energies (as a complement to traditional chemical doping) is noted.

Analysis of the interrelation between magnetic and superconducting subsystems of RE(Rh1 − xRux)4B4 compounds by the examples of compounds DyRh3.8Ru0.2B4 and HoRh3.8Ru0.2B4

The complex way and the importance of solving the problem of coexistence of cooperative magnetism and superconductivity are emphasized by the example of a large group of borides of rare-earth and platinum metals with the general formula RE(Rh1 − xRux)4B4 and cluster structure of the LuRu4B4 type. To analyze the influence of the magnetic subsystem on Bc2(T), the Werthamer, Gelfand, and Hohenberg (WGH) theory is used, based on which, calculated dependences χ(T), which agree with the experimental results, are found. It is shown that by purposefully varying the magnetic subsystem a superconducting one can be formed and the dependence Bc2(T) required for it can obtained. Such approach is also recommended for strong-field superconductors—complex arsenides of iron and lanthanum with fluorine additives.

Superconductivity and magnetism of complex rhodium borides

A number of complex rhodium borides with an LuRu4B4-type structure is synthesized; these are DyRh4B4 (samples HP) with Tc ≈ 4.5 K, DyRh3.8Ru0.2B4 (samples AM) with Tc ≈ 4.5 K, Dy0.8Er0.2Rh3.8Ru0.2B4 (samples AM) with Tc ≈ 6.3 K, and HoRh3.8Ru0.2B4 (samples AM) with Tc ≈ 6.0 K. The temperature dependence of upper critical field Bc2(T) for all the samples under study exhibits an anomalous behavior. In all cases, the curve Bc2(T) demonstrates a point of inflection, after which the curve deviates from the classical parabolic law abruptly upward for DyRh4B4 and DyRh3.8Ru0.2B4 (the 1st group of compounds) and downward for the Dy0.8Er0.2Rh3.8Ru0.2B4 and HoRh3.8Ru0.2B4 compounds (the 2nd group). These compounds are found to be characterized by of the following phase transitions: paramagnet → ferrimagnet → superconductor (retained ferrimagnetism) → antiferromagnet (retained superconductivity). The latter transition to the antiferromagnetic state occurs only in the compounds of the 1st group. It is found that, for the DyRh3.8Ru0.2B4 compound, no traditional Meissner effect is observed but the so-called Volleben effect (paramagnetic Meissner effect) takes place.

Neutron diffraction study of RuSr2(Nd,Ce4+)2Cu2O10−δ

The crystal structure of the phase produced from the RuSr2(Nd0.7Ce0.3)2Cu2O10−δ (RuNd-1222) batch was studied by neutron diffraction at 290, 150, 50, 2, and 1.4 K. The composition of the phase was determined more precisely, in particular, the neodymium-to-cerium ratio was found to be close to the batch ratio and the oxygen content was determined. The temperature dependences were determined for the interatomic distances, the tilt and rotation angles of the RuO6 polyhedron, and the CuO(3)Cu and RuO(1)Ru bond angles. As temperature decreases, the rotation angle of the RuO6 polyhedron increases, while the tilt angle decreases. Magnetic susceptibility measurements showed magnetic ordering at Tm = 115 K in this phase. Comparative analysis of the structural parameters and Tm value for the RuNd-1222 phase and the known RuSm-1222 and RuGd-1222 phases was carried out.