Solid State Phenomena Vols. 152-153

Abstract: Ultrahigh-resolution photoemission spectroscopy of 1T-Fe0.5TiSe2 was performed in order to study the changes in the density of states across the superconducting transition. We observed the gap about 2 meV in spectrum measured at 4.5 K.

Abstract: We investigate the interplay between the BCS and 2D Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) states in the dirty thin ferromagnetic metal/superconductor (FM/S) nanostructures. For the FM/S bilayers we have derived the dependencies of critical temperature on the FM layer exchange field, electronic correlations and thickness. Moreover, in the corresponding FM/S/FM trilayers we predict two new π phase superconducting states with electron-electron repulsion in the FM layers. The 2D modulated LOFF states are possible in such trilayers only in presence of a weak magnetic field and at suitable parameters of the FM and S layers. On this base we originally propose the method of proximity effect probe the magnitude and sign of the electronic correlations, the order parameter symmetry and exchange fields in various FM layers.

Abstract: The proximity effect of the ferromagnetic metal/superconductor (FM/S) bilayers in а external longitudinal magnetic field is considered in the dirty limit. The critical temperature and the superconducting current distribution versus applied magnetic field’s magnitude, film’s thicknesses and a transparency of the contact is calculated, with taking into account аn umklapp processes possibility on the interface of the FM/S contact. It is shown that superconducting current is strictly inhomogeneous and asymmetrical. It is shown also that the current inhomogeneity depends heavily from the FM/S interface transparency.

Abstract: The Low Temperature Heat Capacity of the layered structure Nd3Ni13-xCoxB2 (x = 0, 1, 3, 6, 8, 11 and 13) solid solutions has been measured from 350 mK to 300 K. For high Co content (x ≥ 8), a hyperfine contribution has been explained as due to hyperfine fields of 112.4 kG for Co and 3.68 MG for Nd. The electronic heat capacity contribution reveals an increase of the density of states at the Fermi level as the Co content is increased. For x = 0 a low dimensionality magnetic transition attributed to the Nd sublattice is observed. The substitution of Ni by Co (1  x < 3) induces interaction disorder on the Nd sublattice. For Nd3Ni13B2 an estimation is given for the molecular field of Hm = 54 kG and the exchange constant of J/kB = 4.1 K.

Abstract: The anisotropic magnetic properties of the metallic layered compound with hexagonal crystal structure 2H-NbSe2 are investigated as a function of their dependence on high-energy electron irradiation. Pauli paramagnetism of free electrons is shown to dominate the magnetic susceptibility, P. The anisotropy is related to spin-orbit effects on the hybridized electronic states. Irradiation affects the density of states at the Fermi surface, increasing both P and the anisotropy. Below a threshold temperature, TS=54 K, the paramagnetic contribution, which increases with the dose, is ascribed to dangling bonds, nanotubes and nanorods generated by irradiation.

Abstract: Definite regularity in the distribution of ferromagnetic, antiferromagnetic and superconducting elements is observed in the periodic table starting with the 4-th period. These trends were explained by distinction of degree of division of the d (f)- or р-orbitals of neighboring atoms in the crystal. We calculated also the radii of the external d (f)- and р-orbitals and the nearest to them orbitals with the Slater’s method. It is demonstrated that in the superconducting crystals the d-shells approach the nucleus of neighboring atoms are much closely those for ferromagnetic or antiferromagnetic crystals.

Abstract: The phase transition of Nb/Cu0.41Ni0.59/Nb triple layers from the normal to the superconducting state has been studied experimentally by measuring the temperature dependence of the electrical resistance, R(T). It is shown that the shape of the R(T) curves is different depending on the Cu0.41Ni0.59 thickness. To explain the experimental data we developed a qualitative model which makes more evident the interconnection between the superconducting phase transition and the 0 to  crossover in SFS structures.

Abstract: We investigate the properties of a thin-walled superconducting shell placed in electrical contact with a ferromagnetic cylinder embedded in the superconductor. The case of a superconductor surrounded by the ferromagnet is also considered. Associated with the orbital effect, spontaneous vortex states may appear, characterized by different winding numbers. Special attention is paid to the switching between states of different vorticities and to the behaviour of the critical temperature caused by an external field.

Abstract: The magnetic and X-ray diffraction measurements of the ferromagnetic compounds (MnCo)1-xGe have been performed for the concentration range 0 ≤ x ≤ 0.05. The structural and magnetic phase diagrams have been obtained. Compositions for which the magnetic transition from ferromagnetic to paramagnetic state coincides with the structural transition from an orthorhombic to a hexagonal phase have been determined to be 0.015 ≤ x ≤ 0.025. It was found that for the compound with x = 0.015 application of 1 T magnetic field in isothermal regime in the vicinity of the Curie temperature is accompanied by the entropy change 1.3 J/(Kkg).

Abstract: The three-dimensional model for the theoretical description of the phase transformations and the magnetocaloric effect in shape – memory Heusler Ni2+xMn1-xGa alloys (x=0.18 – 0.27) with a coupled magnetostructural phase transition by the classical Monte Carlo method is proposed. It is shown that the isothermal magnetic entropy change upon magnetic field variations from 0 to 5 T and other magnetic properties are in good agreement with the available experimental data.