[en] Samples of Nd₂Fe_17-xT_xC_y with T=V, Nb, Cr, and Zr were prepared by melting of the constituent elements including C and studied by neutron diffraction. Comparing with their uncarbided counterparts, we found that the substituents transfer, more or less, from the 6c site to the 18f and 18h sites with the introduction of C atoms. This behavior appears to relate to the electronegativities between the C atoms and the early transition series elements because the 18f and 18h sites are near neighbors of the interstitial C site. However, the C effects in the V, Nb, Cr, and Zr samples are not as strong as those in Ti samples. SQUID measurements show that the Curie temperatures of these samples depend on both the interstitial C atoms and the substituents. copyright 1997 American Institute of Physics

[en] Recent developments in rare earth intermetallic materials which may be suitable for bonded magnets are reviewed. These include isotropic coercive powder with a refined grain structure, isotropic single-phase powder showing remanence enhancement, exchange-coupled hard/soft nanostructures, anisotropic coercive powder, and two-phase dipole-coupled powders. Most of these new materials are based on Nd₂Fe₁₄B or Sm₂Fe₁₇N₃. copyright 1997 American Institute of Physics

[en] The effect of Fe doping (<20%) on the Mn site in the ferromagnetic (x=0.37) and the antiferromagnetic (x=0.53) phases of La_1-xCa_xMnO₃ has been studied. Upon doping, no appreciable structure changes have been found in either series. However, conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. These results are not due to the strong lattice effects commonly seen in doping of the La sites. Rather, replacement of Mn³⁺ by Fe³⁺ depopulates the hopping electrons, and weakens the double exchange. The effect of Fe doping can be explained in terms of the band structure. copyright 1997 American Institute of Physics

[en] The La endash Ca endash Mn endash O (LCMO) system grown on lattice matched LaAlO₃ substrates by pulsed laser deposition (PLD) has attracted much recent attention because of the colossal magnetoresistance exhibited. Interest in these materials is because of their potential application in the magnetic recording industry where one of the challenges is to integrate the chip signal-conditioning circuits together with the sensing elements. We have previously reported the giant magnetoresistance characteristics of La endash Ca endash Mn endash O films grown on Si (100) substrates by PLD. Although magnetoresistance at 50 K under a field of 4.7 T was more than 35% (Δρ/ρ₀), no colossal magnetoresistance values were present, clearly due to the imperfections introduced by the lattice mismatch between film and substrate. In this paper we report the transport properties and colossal magnetoresistance behavior in LCMO/CeO₂/Si(100) multilayers grown by PLD. The CeO₂ is attractive as a buffer layer due to its lattice constant, a, of 5.411 Angstrom, which is close to that of silicon (the misfit factor, being only 0.35%). And by simply rotating the unit cell 45 degree in the basal plane, the mismatch is less than 0.16% with LCMO along the a endash b plane. It is found that the LCMO/CeO₂/ Si(100) multilayers also exhibit a well-defined peak of resistivity versus temperature, a similar behavior to a single LCMO layer on a Si substrate. A magnetoresistance value of more than 93% (Δρ/ρ₀) was obtained at 77 K under a field of 12 T. The films have been characterized by vibrating sample magnometer, four-point probe and scaning tunneling microscopy, and details of the influence of the multilayer preparation parameter will also be discussed. copyright 1997 American Institute of Physics

[en] The magnetic penetration depth in the vortex state of YBa₂Cu₃O_6.95 has been measured as a function of temperature T and magnetic field H applied along the c axis. The internal field distribution in single crystals was fit assuming a triangular vortex lattice with an average in-plane penetration depth λ_ab=(λ_aλ_b)^1/2=1155(3) Angstrom, extrapolated to T=0 and H=0; λ(H,T) increases with both T and H. The large T-independent increase in λ_ab with H is attributed to a strong nonlinear response as a result of the unconventional pairing in the superconducting state. copyright 1997 The American Physical Society

[en] The carrier concentration dependence of the spin pseudogap phenomenon in LaBa₂Cu₃O_y has been studied by means of the NMR/NQR method. From the T dependence of 1/T₁T of the planar Cu site, it has turned out that the characteristic temperature for the spin pseudogap at the staggered mode is a monotonic function of hole concentration in the lightly doped region. However, a spin-gap-like behavior was observed even in the optimally doped sample (y=6.96), where the maximal superconducting transition temperature (T_c) is realized as a function of hole doping. This feature is quite different from that in YBa₂Cu₃O_y, where the spin pseudogap is restricted to the lightly doped region and is not observed in the optimally doped sample (y=6.98). Together with 1/T_2G and Knight shift data, the nature of the gap is discussed. copyright 1997 The American Physical Society

[en] Multilayered composites consisting of LaPO₄ (La-monazite) layers alternating with various ZrO₂-based materials were fabricated to investigate whether LaPO₄ provides a weakly bonded interface suitable for promoting toughening, as previously observed in the system LaPO₄/Al₂O₃. The following ZrO₂-based materials were assessed: Y-ZrO₂, Y-ZrO₂/Al₂O₃, Ce-ZrO₂, and Ce-ZrO₂/Al₂O₃. Debonding was observed in all cases. The composites containing Y-ZrO₂ and Y-ZrO₂/Al₂O₃ were stable, with no reactions, at temperatures up to at least 1,600 C. However, in the composites containing Ce-ZrO₂, interdiffusion of Ce and La occurred, resulting in formation of a pyrochlore-like phase and, in the case of the Ce-ZrO₂/Al₂O₃ composite, a (Ce,La)Al₁₁O₁₈ magnetoplumbite phase

[en] Multilayer system W/Si have been obtained on oxidized Si substrate by means magnetron spraying. Then samples were heated in 950 C. Created structures and processes occurring at the films boundary e.g. melting, diffusion, silicides formation have been observed by means of RBS method. 6 refs, 1 fig

[en] Sublimation recovery of zirconium tetrafluoride and its pyrohydrolysis in the course of reprocessing Algoma baddeleyite-zirconium ores by ammonium hydrofluoride have been studied. Practicability of zirconium recovery (with a high yield) from the concentrate by means of ZrF₄ sublimation in inert medium and Zr(2) oxide preparation by hyrohydrolytic decomposition has been considered. 6 refs., 3 figs., 2 tabs

[en] Short communication