[en] The possibility of utilizing the Moessbauer reflection technique based on the detection of the internal conversion electrons was envisaged soon after the discovery of the effect. The typical application of this technique is study of the surface properties after various treatments. 33 refs, 30 figs, 3 tabs

[en] The growth of Bi-Pb-Sr-Ca-Cu films by liquid phase epitaxy is described. Films consisting of Bi_2-yPb_ySr_3-xCa_xCu₂O_8+z (2212 phase) and Bi_2-yPb_ySr_2-xCa_xCu₂O_6+z (2201 phase) are grown. Good quality single crystal films result. The melt composition and film stoichiometry vary. For the 2212 phase the effects of the Ca and Pb stoichiometry on both the structural and superconducting properties are discussed. Furthermore the c lattice parameter of the 2212 films is found to increase linearly with the Ca content per formula unit with a slope of 0.3 A per 0.5 Ca atoms per formula unit. No sizeable changes in the superconducting properties are found for films with a Ca content between 0.8 and 1.3 atoms per formula unit. Lead doping is shown to decrease the transition temperature without broadening the transition itself; 0.4 lead atoms per formula unit decrease the transition temperature down to 69K. The transport properties of these films are also discussed and the critical current density is shown to depend on the particular substrate chosen. (orig.)

[en] Moessbauer spectroscopy has shown that there are at least three magnetic phases of samarium iron garnet and possibly five, if spin reorientations that are not abrupt are assumed to occur between these phases. The easy magnetic axes are: [111], 560>T> or approx. =60 K; [110], approx. 45>T> or approx. =18 K; [100], approx. 10>T > or = 5 K. The spin reorientations are estimated to occur between approx. 60 and approx. 45 K and between approx. 18 and approx. 10 K. While the phases with the [111] and [110] easy magnetic axis have been reported before, this is the first report of the lowest-temperature phase with [100] easy magnetic axis, and of the possible spin reorientations. If the latter exist, the lowest-temperature phase can not be tetragonal; it is most likely orthorhombic. The sequence of magnetic space groups is: R3c', [111] → F2'/d' → Fdd'd', [110] → I2'/c' → Ibc'a', [100]

[en] Critical currents carried by Bi-Sr-Ca-Cu-O superconducting samples have been measured as a function of temperature and of a weak applied magnetic field. Both polycrystalline samples, of the 2212 (T _c = 85K) and 2223 (T _c = 110K phases, and single crystals of the 85K phase have been investigated. For sintered samples the critical current density, at a temperature of 0.65T _c , is lower than 50 A/cm ² and is strongly reduced in a field of few tens of Gauss. In the single crystals investigated the critical current density are of the same order of magnitude. However in these samples the temperature dependence is markedly different from the one observed in sintered specimens, and is not affected by the presence of weak applied field

[en] Superlattices based on standard high temperature superconductors (HTS) such as YBa₂Cu₃O_7-x and Bi₂Sr₂Cu_nCa_n-1O_x have been extensively used to investigate many fundamental issues in HTS physics such as dimensionality, vortex dynamics, proximity effects, epitaxial strain effects, interplay between superconductivity and magnetism. Recently, a different approach based on thin layers of the (Ca, Sr, Ba)CuO₂ compounds (infinite layers compounds) has been applied to the synthesis of superconducting cuprate heterostructures. Ideal infinite layer (IL) compounds alone are not superconducting; however, in IL-based heterostructures, the occurrence of charge transfer among layers containing different alkaline earth ions can give rise to superconductivity. Structural features of these heterostructures can be engineered in a wide range and, consequently, their superconducting properties are studied. The highlights of these investigations are reviewed here. (topical review)

[en] Novel microwave absorption and dispersion measurements have been performed on well-characterized single-crystal platelets of the high-T/sub c/ superconductor YBa₂Cu₃O/sub 7-x/. The results are explained in terms of the rapid variation of the penetration depth near and below T/sub c/. Since EPR measurements are very sensitive to small changes in absorption and dispersion, this technique should be very useful in the understanding of the transition temperature region in both new and old superconducting materials

[en] Films of Bi₂Sr₂CaCu₂O/sub 8+//sub x/ have been grown from KCl solution. Gadolinium gallium garnet substrates (1 1 1) oriented have been used. The films resulted highly textured with the c axis perpendicular to the substrate surface. The onset of the resistive transition was 85 K, while zero resistance was obtained at 50 K. This technique is particularly promising in view of the possibility to grow large epitaxial films of both the Bi₂Sr₂CaCu₂O/sub 8+//sub x/ and the Bi₂Sr₂Ca₂Cu₃O/sub 10+//sub x/ phases

[en] In the present work we report structural and transport properties of epitaxial SrRuO₃ films grown by laser molecular beam epitaxy (Laser MBE) equipped with in-situ reflection high energy electron diffraction (RHEED) analysis at very low oxygen pressure (less than 10^-4 mbar). Several works have given first evidence of a strong correlation between transport and magnetic properties and structural properties of SrRuO₃ (such as the influence of the strain, substrate-film interface, etc.). We worked on the determination of the conductive and magnetic properties of SrRuO₃ films as a function of the strain. Different strains were induced varying the SrRuO₃ films thickness from ultrathin (few unit cells) to thick (thousands of Angstrom) structures. Superlattices based on SrRuO₃ and SrTiO₃ films were also grown. In such a structure, the largest value of strain was achieved and the transport properties confirm our simple SrRuO₃ conducting model. (orig.)

[en] Preliminary results on high Tc superconductors are reported. One of Y-Ba-Cu-O compound system has been fabricated. The temperature dependence of the resistance has been determined. The critical temperature of the samples annealed in Oxygen atmosphere is well above the normal boiling point of liquid nitrogen

[en] Novel microwave absorption and dispersion measurements have been performed on polycrystalline samples and well-characterized single-crystal platelets of high-T/sub c/ superconductors YBa₂Cu₃O/sub 7-//sub x/. The results are explained in terms of fluxoids and rapid variation of the penetration depth near and below T/sub c/. The microwave absorption increases as a function of the magnetic field as a result of increase in the surface area of the normal-conducting region. By applying a modulating field in a particular manner and from thermodynamic considerations there are strong indications of energy absorption by fluxoids