Enhanced magnetoresistance in pulsed laser deposited stable chromium oxide thin films

Granular thin films of primarily rutile type tetragonal chromium dioxide (t-CrO2), along with a minor phase of hexagonal Cr2O3 were deposited on rutile type TiO2 layers by KrF excimer laser based pulsed laser deposition (PLD) technique using Cr2O3 targets. The TiO2 under-layer was also deposited by PLD process on oxidized Si substrates followed by annealing at 1100 degrees C for 10-15 min under O-2 ambient. The lattice-matched interfacial TiO2 layer stabilizes the metastable Cr (IV) phase of CrO2, otherwise it readily converts into its stable phase of Cr (III) oxide, Cr2O3, under ambient conditions. Studies with X-ray diffraction (XRD) and Raman spectroscopy confirmed the stable t-CrO2 phase in the films. The microstructure in the films was studied with field emission scanning electron microscope (FESEM) and magnetic force microscope (MFM). As revealed by electrical analysis, the ferromagnetic (FM) t-CrO2 grains in conjunction with the antiferromagnetic (AFM) Cr2O3 phase in the tailored thin films effectively support an electrical transport process based on inter-granular spin-dependent tunneling (SDT) mechanism, giving rise to significantly high magnetoresistance (MR). A typical sample exhibits a markedly improved MR-value, viz., -30% at an applied field (H) of 438 kA/m at 278 K, than reported values in CrO2 thin films. Such a large MR value in the Coulomb blockade regime arises primarily not only because of the considerably suppressed spin flipping but also as a result of the highly effective SDT mechanism through an interlinked FM-AFM structure of chromium oxides in this specially engineered microstructure of the thin films. Such type of stable half-metallic thin films with low-H switching behavior is attractive for pertinent use in spintronics and magnetic sensing based applications.