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Many efforts are under way to control the structure of heterointerfaces in nanostructured composite materials for designing functionality and engineering application. However, the fabrication of high-quality heterointerfaces is challenging because the crystal/crystal interface is usually the most defective part of the nanocomposite materials. In this work, we show that fully dense insulator (MgO)/semiconductor(Mg2Si)/superconductor(MgB2) nanocomposites with atomically smooth and continuous interfaces, including epitaxial-like MgO/Mg2Si interfaces, are obtained by solid phase reaction between metallic magnesium and a borosilicate glass. The resulting nanocomposites exhibit a semiconductor-superconducting transition at 36K owing to the MgB2 nanograins surrounded by the MgO/Mg2Si matrix. This transition is followed by the intergrain phase-lock transition at ~24K due to the construction of Josephson-coupled network, eventually leading to a near-zero resistance state at 17 K. The method not only provides a simple process to fabricate dense nanocomposites with high-quality interfaces, but also enables to investigate the electric and magnetic properties of embedded superconducting nanograins with good intergrain coupling. [ABSTRACT FROM AUTHOR]

The microscopic magnetic properties of high-quality GdN thin films have been investigated by electron spin resonance (ESR) and ferromagnetic resonance (FMR) measurements. Detailed temperature dependence ESR measurements have shown the existence of two ferromagnetic components at lower temperatures, which was not clear from the previous magnetization measurements. The temperature, where the resonance shift occurs for the major ferromagnetic component, seems to be consistent with the Curie temperature obtained from the previous magnetization measurement. On the other hand, the divergence of line width is observed around 57K for the minor ferromagnetic component. The magnetic anisotropies of GdN thin films have been obtained by the analysis of FMR angular dependence observed at 4.2K. Combining the X-ray diffraction results, the correlation between the magnetic anisotropies and the lattice constants is discussed. [ABSTRACT FROM AUTHOR]

We investigate the interaction between superconductivity and defect-induced d0 ferromagnetism using a composite consisting of MgB2 and MgO nanocrystals. The composite exhibits a ferromagnetic hysteresis behavior in the temperature region from 40 to 300 K. Defective MgO nanocrystals (~20 nm) embedded in the composite are considered to be responsible for the observed ferromagnetism. The zero field cool and field cool magnetization curves show that the superconducting transition occurs at Tc = 38.6K, in agreement with Tc of pure MgB2. In the temperature region from Tc to 0.9Tc (~35 K), the magnetization hysteresis curves show a superposition of ferromagnetic (F) and superconducting (S) signals. When the temperature of the system is decreased below 0.65Tc (~25 K), the S signals dominate over the F signals. The resulting magnetic hysteresis loops are highly asymmetric and the descending filed branch is nearly flat, as predicted in the case of surface pinning. At temperatures below 0.5Tc (~20 K), a sharp peak is developed near zero field in the magnetization hysteresis curves, implying an enhancement of superconducting vortex pinning. The observed pinning enhancement most likely results from magnetic pinning due to randomly distributed magnetic MgO grains, which yield the magnetic inhomogeneity and the related pinning potential in a length scale of ~100nm. Thus, the present ferromagnetic/superconducting composite provides an ideal model system that demonstrates the availability of d0 ferromagnetism as a source of magnetic potential for effective vortex pinning. [ABSTRACT FROM AUTHOR]