Tunneling magnetoresistance of hydrothermally sintered La1-Sr MnO3-silica nanocomposites
Résumé
The study deals with tunneling magnetoresistance in a series of composite systems of so-called 0–3 connectivity, in which highly conducting manganite nanoparticles of ferromagnetic groundstate (0-dim objects) are embedded in the (3-dim) insulating matrix of silica. The sample fabrication included the sol-gel preparation of La1–xSrxMnO3 particles of the x = 0.35 composition and 25 nm mean crystallite size, their coating by silica of controlled thicknesses in the 1–5 nm range, and subsequent consolidation by hydrothermal sintering at 300 °C. Temperature dependent electric resistivities of the materials were measured in magnetic fields of 0 and 40 kOe down to 5 K, and field-dependent isothermal curves were taken by sweeping magnetic field up to 140 kOe. The field-dependent effects were interpreted in terms of the low- and high-field magnetoconductance. It is important that extents of these phenomena are markedly independent of the silica amount, despite the five orders change in absolute resistivity values. Microscopic mechanisms of the intergrain transport, applicable to polycrystalline manganites, nanogranular compacts and nanocomposites in general, are proposed.