D. M. Phase

Study of the effect of Mn doping on the BiFeO3 system

In this work a Mn doped magnetoelectric BiFeO3 system is studied. X-ray diffraction (XRD), scanning electron microscopy, energy dispersive x-ray analysis (EDX), Mossbauer spectroscopy at room and high temperatures, differential scanning calorimetry (DSC), high temperature magnetization, dielectric constant measurements and x-ray photoelectron spectroscopy (XPS) are used to characterize the samples. The XRD result shows BiFeO3 as a major phase along with about 1–2% impurity phase. EDX shows the equi-atomic ratio of Bi and Fe site cations. Using DSC it is observed that the Neel temperature decreases with Mn doping. Using Mossbauer and XPS it is observed that Fe exists in the +3 oxidation state. The samples have an antiferromagnetic nature with Mn doping.

Correlation of spectral features of photoluminescence with residual native defects of ZnO thin films annealed at different temperatures

We investigated the effects of post-growth annealing in the temperature range of 873 to 1273u2009K on the spectral features of photoluminescence (PL) vis-a-vis the crystalline and compositional native defects of ZnO thin films grown at 773u2009K by pulsed laser deposition (PLD) on sapphire substrates. It is found in the PL spectra at 10u2009K that the deep level emission (DLE) shifted from red-orange spectral region of ∼1.8–2.4u2009eV to yellow–green region of ∼2.4–2.9u2009eV with the increasing temperature of annealing. We propose that the PL in red-orange region originating from the singly ionized oxygen vacancies diminished due to increased replenishment of oxygen with increasing annealing temperature and that in the yellow–green region originating from the oxygen interstitials and/or zinc vacancies increased due to enhanced concentration of these point defects. As the annealing temperature was increased, the overall intensity of PL in the DLE region increased slightly up to 973u2009K but beyond that it increased steeply and ...

Direct observation of oxygen induced room temperature ferromagnetism in MoO2 thin films by x-ray magnetic circular dichroism characterizations

We report the element specific polarized near edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments on well characterized undoped MoO2 thin films that show ferromagnetism at room temperature. The polarization dependent of Ou2009K edge NEXAFS spectra indicate a strong hybridization of Ou20092p-4d Mo orbitals followed by a strong anisotropy in the electronic properties. An unquenched orbital magnetic moment within the Ou20092p shell is clearly evident from the XMCD Ou2009K edge, which is ferromagnetically coupled to the neighboring Mo moments as confirmed by Mou2009M3,2 edge XMCD experiment.

Study of site-disorder in epitaxial magneto-electric GaFeO3 thin films

Epitaxial thin films of GaFeO3 (GFO) with different thicknesses (22–170u2009nm) are prepared on (001) oriented yttria-stabilized zirconia substrate using pulsed laser deposition. The M-H data measured below Curie temperature (TC) mimic two phase composite magnetic system consisting of hard and soft magnetic phases. The results are explained in terms of Fe distribution among the available cation sites of GFO. Thermo-magnetic irreversibility and cusp in zero-field cooled magnetization are observed for all the films and are explained in terms of the magnetic anisotropy of the GFO.

Band alignment and interfacial structure of ZnO/Ge heterojunction investigated by photoelectron spectroscopy

Studies on band-offset and band-alignment of heterojunction of highly c-axis oriented ZnO thin films grown on n-Ge (1 1 1) by pulsed laser deposition show a type-II band alignment with the valence band offset (ΔEV) of 3.1u2009±u20090.2u2009eV. The valence band spectra of this heterojunction show band onsets corresponding to Ge, interfacial GeOx, and ZnO layers. This observation also enabled us to determine ΔEV of ZnO/GeOx heterojunction to be 1.4u2009±u20090.2u2009eV. These studies provide further insight into the band alignment of ZnO/GeOx/Ge system wherein the observed large value of ΔEV of ZnO/Ge can be used for heterojunction based optoelectronic devices.

Microstructural study of iron nitride thin films deposited by ion beam sputtering

An amorphous iron nitride thin film was deposited using reactive ion beam sputtering of iron by a beam of argon and nitrogen ions. Nitrogen content in the film as determined from conversion electron Mossbauer spectroscopy (CEMS) and X-ray photoelectron spectroscopy (XPS) was FeN 0.7 . The mass density of the film was calculated using energy-dispersive X-ray reflectivity (EDXRR) measurements and is found to be 6.0 gm/cm 3 . CEMS shows that the film is nonmagnetic in nature. Morphology of the film is obtained from atomic force microscopy (AFM). The surface roughness of the film does not increase appreciably beyond that of the substrate even after a deposition of 131 nm of material with these qualities the film is a good candidate for the multilayer superstructure of a nuclear Bragg monochromator of the type 56 FeN 0.7 / 57 FeN 0.7 .

Development of an ion-beam sputtering system for depositing thin films and multilayers of alloys and compounds

Abstract An ion-beam sputtering (IBS) system has been designed and developed for preparing thin films and multilayers of various elements, alloys and compounds. The ion source used is a 3xa0cm diameter, hot-cathode Kaufman type 1.5xa0kV ion source. The system has been successfully tested with the deposition of various materials, and the deposition parameters were optimised for achieving good quality of thin films and multilayers. A systematic illustration of the versatility of the system to produce a variety of structures is done by depositing thin film of pure iron, an alloy film of Fe–Zr, a compound thin film of FeN, a multilayer of Fe–Ag and an isotopic multilayer of 57 FeZr /FeZr. Microstructural measurements on these films using X-ray and neutron reflectivity, atomic force microscopy (AFM), and X-ray diffraction are presented and discussed to reveal the quality of the microstructures obtained with the system. It is found that in general, the surface roughnesses of the film deposited by IBS are significantly smaller as compared to those for films deposited by e-beam evaporation. Further, the grain size of the IBS crystalline films is significantly refined as compared to the films deposited by e-beam evaporation. Grain refinement may be one of the reasons for reduced surface roughness. In the case of amorphous films, the roughness of the films does not increase appreciably beyond that of the substrate even after depositing thicknesses of several hundred angstroms.

Magnetic and electrical behavior of Al doped La0.7Ca0.3MnO3 manganites

The effects of doping on magnetic and electrical transport mechanism of polycrystalline samples La0.7Ca0.3Mn1−xAlxO3 (x=0,0.02,0.04,0.06,0.08,0.1) have been investigated. Magnetization data reveal that long-range ferromagnetic ordering persists in all samples and the saturation moment decreases linearly as x increases. Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of Al in the series leads to a decrease in conductivity of the doped manganites samples, with conduction being controlled by the disorder induced localization of charge carriers.

Synchrotron based photoemission study on the band alignment and interface at ZnO/GaP hetero-junction

Synchrotron based photoemission spectroscopy study shows a type-II band alignment at pulsed laser deposited epitaxial ZnO layer and GaP substrate. Additionally, the ZnO/GaP hetero-junction is comprised of an interfacial GaOx layer. Valence band onsets corresponding to ZnO, GaOx, and GaP materials enabled us to determine the valence band offset (ΔEV) values of 2.81u2009eV, 0.35u2009eV, and 2.46u2009eV at ZnO/GaP, ZnO/GaOx, and GaP/GaOx hetero-junctions, respectively. ΔEV values determined directly from the difference of valence band onsets are in corroboration with that obtained by Krauts method. The band alignment and interface study of ZnO/GaP hetero-junction can be used to design optoelectronic devices.

Infrared spectroscopic study of pulsed laser deposited Fe3O4 thin film on Si (111) substrate across Verwey transition temperature

We present low-temperature infrared measurements of magnetite (Fe3O4) thin films on Si (111) substrate across the Verwey transition temperature (TV). The line parameters of the most intense t1u mode observed in the Fourier transform infra red spectrum of the film is studied as a function of temperature. We observe that mode frequency increases abruptly at 130u2009K, and full width at half maxima of the mode increases abruptly at 113u2009K. The observations point out that structural transition may start earlier at 130u2009K than the actual Verwey transition (121u2009K) and that complete at 113u2009K. These results are consistent with the higher transition temperature as observed in resistivity and magnetization measurements.