Self-assembled Ag-modified multigranular chromium oxide nanocomposite particles in half-metallic CrO2 configuration for efficient room temperature magnetoresistance

Abstract

We report on the embedding of half-metallic ferromagnetic CrO2 phase in self-assembled Ag-modified chromium oxide nanocomposite granular particles for room temperature magnetoresistive applications. The multigranular nanostructure consists of small ferromagnetic domains of rutile-type-tetragonal CrO2 (t-CrO2) & orthorhombic CrO2 (o-CrO2) phases in the matrix of various chromium oxide phases. The matrix consisted of antiferromagnetic and insulating Cr3O8 and Cr2O3 phases as well as paramagnetic Cr2O and CrO3 phases in addition to CrO2. The nanocomposite particles consist of a correlated thin diamagnetic shell layer of silver of discontinuous formation over the core of multigranular chromium oxide nanostructure proficiently engineering the room temperature magnetoresistance (RTMR) properties. The nanocomposite structure possesses ferromagnetic properties predominantly due to the presence of ferromagnetic t-CrO2 &o-CrO2 phases, canted surface spins from antiferromagnetic Cr2O3 behaving as ferromagnetic domains and contribution from paramagnetic phase spins under the effect of magnetic field. Structural information derived from X-ray diffraction (XRD) based Rietveld analysis matched well with those obtained from the selected area electron diffraction (SAED) pattern of the as-synthesized multigranular chromium oxides nanocomposite particles. Fourier transform infrared spectroscopy (FTIR) provided structural bonding characteristics, while Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) gave surface bonding features in deconvoluted spectrum for comprehensive analysis of the as-synthesized multigranular chromium oxides nanocomposite particles. Electrical properties in a typical plot of lnρ vs.T−1/2 showed the half-metallic behaviour characteristic of t-CrO2 in a predominantly spin-dependent tunneling (SDT) mechanism in the heat-treated nanocomposite particles. Cold-pressed compacts of the as-synthesized nanocomposite particles revealed a significantly enhanced RTMR of − 80% under an applied in-plane magnetic field (H) of 3 kOe. The RTMR curves were acquired in two different geometries with H parallel (H || I) and perpendicular to the direction (H ┴ I) of applied current, respectively.