• Sandip Dhara

      Articles written in Bulletin of Materials Science

    • Growth, magnetic properties and the effect of cobalt addition in metal-organic chemical vapour deposited (MOCVD) gamma iron oxide thin films for magnetic recording applications

      Sandip Dhara A C Rastogi B K Das

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      The present study aims at investigating MOCVD technique for the deposition of magnetic oxide thin films using volatile metal-organic compounds as source material. A three-step scheme has been described to form γ-Fe2O3 phase starting from α-Fe2O3 films as-deposited in optically heated atmospheric cold wall CVD reactor. Growth of γ-Fe2O3 in a two-step process has been performed by depositing Fe3O4 phase directly by resistively heated low-pressure CVD (LPCVD) technique. Role of substrate temperature in controlling the oxidation leading to direct formation of metastable γ-Fe2O3 phase (single-step scheme) by atmospheric CVD technique has been described. A new mode of introduction of cobalt in the film, namely heterogeneous dispersion of cobalt in the γ-Fe2O3 matrix, has also been described. Crystallographic structure, microstructure and magnetic properties of the films have been studied in detail. Biaxial vector coil and high-temperature magnetic studies were carried out for determining the nature of anisotropy in the γ-Fe2O3 film. Growth of γ-Fe2O3 films in different schemes have been discussed from the studies of growth kinetics in a cold-and hot-wall-type reactor chambers.

    • Magnetic study above the curie temperature of γ-Fe2O3 in determining the dispersion nature of Co2+ ions in Co-modified γ-Fe2O3 thin films

      B K Das Sandip Dhara A C Rastogi

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      Gamma (γ) iron oxide thin films containing 6 at% of cobalt atoms selectively dispersed at interstitial and octahedral locations have been prepared by a reactive chemical vapour deposition process. Such dispersion gives microscopic Co-trapped and Co-doped regions inγ-Fe2O3 matrix and introduces magnetocrystalline anisotropy leading to high coercivity values of 64–112 kA/m. Temperature dependence of coercivity and saturation magnetization forγ-Fe2O3 films confirm the dispersion model.

    • Medium resolution magneto-optical Faraday rotation measurement system

      Sandip Dhara V N Moorthy A C Rastogi B K Das

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      Medium resolution magneto-optic Faraday rotation measurement setup has been reported. Measuremental setup reported is made up of simple polarized laser source, beam expander, analyzer and a bisected cross polarizedp-n detector for single ended measurements. Result of CoO modified yttrium iron garnet (YIG) films showed a rotation of 3 deg/μm which is comparable to earlier reported Co-doped YIG films.

    • Effect of post deposition reduction treatment of YIG thin films on stabilizing cubic garnet phase

      A C Rastogi V N Moorthy Sandip Dhara H P Gupta B R Awasthy B K Das

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      Yttrium iron garnet thin films have been prepared by low pressure metallo-organic chemical vapour deposition method (MOCVD). Dipivaloyl methanates of yttrium and iron have been used as the precursors in the MOCVD growth of the garnet films. Post deposition O2 annealing at 900°C is required to form a garnet phase which also shows orthoferrite and component Y2O3 and α-Fe2O3 phases. We show that a partial H2 reduction treatment minimizes secondary phases and stabilizes the garnet phase. These treatments also enhance the magnetic properties considerably.

    • Unique identification of phonon modes using polarized Raman studies of SnO(001) crystals..

      RAKTIMA BASU D SORNADURAI S AMIRTHAPANDIAN SANDIP DHARA

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      Stannous oxide (SnO), an exclusive p-type oxide semiconductor in the oxide family, is a source of renewed interest because of its ability to be an excellent anode material. So far, there are very few reports on the vibrational propertiesof SnO and controversy remains in the assignment of vibrational modes. Textured single crystals of SnO were synthesized by a one-step solvothermal method. The as-synthesized SnO crystals have a wide (001) plane, as confirmed by high resolution transmission electron microscopy images. Raman spectroscopy is used for the identification of phase as well as crystalline orientation. Moreover, a unique assignment of phonon modes in SnO is also performed using polarized Raman spectroscopic studies for different orientations around c-axis of the crystalwith the incident electric field vector. Thus, a novel methodologyof phonon assignment is adopted with a minimum amount of data collection for a diatomic molecule having a tetragonal symmetry with a number of symmetry elements.

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