Surface stabilized GMR nanorods of silver coated CrO2 synthesized via a polymer complex at ambient pressure

Stable anisotropic nanorods of surface modified CrO2 (∼18 nm diameter) with a correlated diamagnetic layer (2-3 nm thickness) of silver efficiently tailors useful magnetic and magnetoresistance (MR) properties. Essentially, it involves a core-shell structure that is developed by displacing part of Cr4+ ions by Ag atoms on the CrO2 surface (topotactic surface layer) via an etching reaction of a CrO2-polymer complex with Ag+ ions in hot water followed by heating the dried sample at 300-400 °C in air. The stable Ag-layer so obtained in the form of a shell protects CrO2 such that it no longer converts to Cr2O3 in ambient pressure during the processing. X-ray diffractogram of the Rutile type tetragonal CrO2 structure (lattice parameters a=0.4429 nm and c=0.2950 nm) includes weak peaks of a minority phase of an fcc-Ag (a=0.4086 nm). The silver surface layer, which manifests itself in a doublet of the 3d5/2 and 3d3/2 X-ray photoelectron bands of binding energies 368.46 eV and 374.48 eV, respectively, suppresses almost all Cr bands to appear in a measurable intensity. The sample exhibits a distinctly enhanced MR-value, e.g., (−) 7.6% at 77 K, than reported values in compacted CrO2 powders or composites. Such a large MR-value in the Coulomb blockade regime (<100 K) arises not only due to the suppressed spin flipping at low temperature but also from a spin dependent co-tunneling through an interlinked structure of silver and silver coated CrO2 nanorods.