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IIT Jodhpur

We report on the defect structure and composition of vacuum-annealed In2O3 (VA-In2O3) ferromagnetic thin films. VA-In2O3 is highly (∼7 at.%) oxygen deficient. High-resolution microscopy reveals disordered glassy surface layers and crystalline defect states, O and In vacancies, and In-In clustering, predominantly in the vicinity of the surface. These defects are not observed in as-deposited In2O3 films. These structural defects are important for understanding many of the novel properties found in non-stoichiometric In2O3, including high conductivity and room-temperature ferromagnetism. © 2009 Acta Materialia Inc.

World University root node

Department of Physics

Scripta Materialia

Coexistence of anion and cation vacancy defects in vacuum-annealed In2O3 thin films

We have synthesized a range of transition-metal-doped BiFeO3 thin films on conducting silicon substrates using a spin-coating technique from metal-organic precursor solutions. Bismuth, iron and transition-metal-organic solutions were mixed in the appropriate ratios to produce 3% transition-metal-doped samples. X-ray diffraction studies show that the samples annealed in a nitrogen atmosphere crystallize in a rhombohedrally distorted BiFeO3 structure with no evidence for any ferromagnetic secondary phase formation. We find evidence for the disappearance of the 404cm -1 Raman mode for certain dopants indicative of structural distortions. The saturation magnetization of these BiFeO3 films has been found to increase on doping with transition metal ions, reaching a maximum value of 8.5emucm-3 for the Cr-doped samples. However, leakage current measurements find that the resistivity of the films typically decreases with transition metal doping. We find no evidence for any systematic variation of the electric or magnetic properties of BiFeO3 depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grainboundaries. © 2009 IOP Publishing Ltd.

Journal of Physics Condensed Matter

Structural, magnetic, and electrical studies on polycrystalline transition-metal-doped BiFeO3 thin films

We have investigated the structural, optical, and electrical properties of both as-grown and vacuum annealed In2 O3 thin films. In contrast to the insulating as-prepared samples, vacuum annealed In2 O3 films exhibit a metallic electrical conductivity with increased carrier concentration and mobility. We attribute the excess carriers to an oxygen deficiency introduced during vacuum annealing. Remarkably, these carrier densities seem to be stable under ambient conditions for at least two years. Optical spectroscopy measurements show a large optical transparency, greater than 80%, for both the as-prepared and vacuum annealed In2 O 3 films. © 2009 American Institute of Physics.

Fulltext

Applied Physics Letters

Undoped vacuum annealed In2 O3 thin films as a transparent conducting oxide

We have investigated the effects of UV irradiation on the electrical and optical properties of polycrystalline In2 O3 films. We found that UV illumination at a peak wavelength of 365 nm leads to a sharp drop in resistance and increase in carrier concentration. This highly conductive state persists for a timescale of hours in air at room temperature after illumination. We observe distinct changes in the optical absorption spectra and the associated change in carrier concentration, which is consistent with a Burstein-Moss shift of ∼0.1 eV. The relaxation rate of this persistent conducting state depends strongly on temperature. We find that the conductance relaxation in an oxygen-free environment can be described by a stretched exponential while the behavior of the samples in air is better described by a logarithmic relaxation, both of which may be associated with glassy behavior. © 2009 American Institute of Physics.

Robust room temperature persistent photoconductivity in polycrystalline indium oxide films

We have fabricated InN thin films using rf magnetron sputtering from an indium (In) metal target. Optical and electrical measurements show that these as-grown films are n -type with carrier concentrations ranging from 10 20 to 1021 cm-3. This variation in carrier density is produced by controlling the conditions during the deposition. We used Rutherford backscattering spectrometry to identify possible sources for n -type carriers. We found that in addition to strong direct bandgap optical absorption ranging from 1.4 to 2.0 eV, a large plasmon absorption peak in the infrared region (0.45-0.8 eV) is also observed. This tunable IR absorption suggests that these highly degenerate InN films could be used for a number of applications, including optical filters and infrared devices. © 2009 American Institute of Physics.

Journal of Applied Physics

Strong plasmon absorption in InN thin films

We report on the electric-field tuning of a magnetic phase transition temperature (TL) in multiferroic Ni3V2O 8 thin films. The simultaneous magnetic and ferroelectric transition in Ni3V2O8 exhibits a clear dielectric anomaly; we monitored TL under applied electric and magnetic fields using dielectric measurements. The transition temperature increases by 0.2 K±0.05 K when the sample is biased approximately 25 MV/m compared to zero bias. This electric-field control of the magnetic transition can be qualitatively understood using a mean-field model incorporating a tri-linear coupling between the magnetic order parameters and spontaneous polarization. The shape of the electric field-temperature phase boundary is consistent with the proper order parameter for the multiferroic phase in Ni3V 2O8 being a linear combination of the magnetic and ferroelectric correlation functions. © EPLA, 2009.

Electric-field control of a magnetic phase transition in Ni 3V2O8

We have studied phase transitions in multiferroic Ni3V2O8, through dielectric measurements and by investigating the effects of Zn doping. The divergence of the dielectric constant near TL = 6.4 K can be approximately fit by power law behaviour, but exhibits different critical exponents above and below TL. The two higher temperature magnetic transitions in (Ni1-xZnx)3V2O8, are strongly suppressed as the Zn doping fraction x is increased. The rates of the suppression of both TH and TL with x are consistent with two-dimensional spin systems, with the suppression of TH consistent with Ising spins and the suppression of TL consistent with Heisenberg spins.

Philosophical Magazine

Scaling behaviour of magnetic transitions in Ni3V2O8

We have probed changes in the magnetic, electrical, dielectric, optical, and thermodynamic properties of iron vanadate (FeVO4) at two magnetic phase transitions. FeVO4 exhibits two antiferromagnetic transitions at TN1 = 22K and TN2 = 15K. Below 15K FeVO4 develops an electric polarization, concomitant with the second antiferromagnetic transition and indicating strong magnetoelectric coupling. The powder averaged zero field electric polarization for the polycrystalline FeVO4 sample is 6μCm-2 and can be switched by reversing the poling voltage. The peaks for certain Raman modes at larger wavenumbers shift to slightly higher energies in the temperature range between TN1 and TN2, but there is practically no change in the Raman spectra between the paramagnetic and ground states. These Raman features help to clarify the microscopic mechanisms for magnetoelectric coupling in FeVO4. © 2009 IOP Publishing Ltd.

Development of electrical polarization at an antiferromagnetic transition in FeVO4

Composite nanoparticles of aerosol OT-alginate hydrogel loaded with Fe 3 O4 and rhodamine 6G (R6G) in average diameter between 25 nm and 50 nm were synthesized by emulsification-cross-linking process and characterized by transmission electron microscopy (TEM) and SQUID magnetometery measurements. TEM measurements show that the Fe3 O4 particles are uniformly distributed within AOT-alginate nanoparticles. The Ca 2+ cross-linked AOT-alginate nanoparticles loaded with Fe 3O4 and rhodamine showed superparamagnetic behavior at room temperature with saturation magnetization of ∼50 emu/g of Fe 3O4. Similar behavior was exhibited by Fe 2+ crosslinked AOT-alginate nanoparticles loaded with Fe3O4 and rhodamine except it showed twice the magnetization of Ca 2+ crosslinked counterpart. A decrease in the amount of rhodamine loading for the composite nanoparticle systems as compared to the bare AOT-alginate nanoparticles was found. © 2008 IEEE.

IEEE Transactions on Magnetics

Fe3O4 incorporated AOT-alginate nanoparticles for drug delivery

We report the structural and optical properties of x SnO2 -y Fe2 O3 nanocrystalline composite thin films. SnO2 and Fe2 O3 exhibit strong phase separation instability and their particle size and crystallinity are tunable by changing their composition and annealing temperature. The bandgap for these composites continuously increases from 2.3 to 3.89 eV. We discuss the increasing bandgap values in terms of the quantum confinement effect manifested by the decreasing size of Fe2 O3 crystallites. The method provides a generic approach for the tuning of the bandgap in nanocomposite systems. © 2008 American Institute of Physics.

Bandgap engineering by tuning particle size and crystallinity of SnO 2 - Fe2O3 nanocrystalline composite thin films

We have investigated the properties of sputter deposited InN thin films prepared from an In-metal (InN-MT) and an In2O3 target (InN-OT). The excess oxygen present in the InN-OT films alters the microstructure by introducing additional disorder. Depth dependent x-ray photoelectron spectroscopy measurements indicate the presence of higher concentrations of oxygen in InN-OT. Raman spectra show evidence for the presence of an In2O3 secondary phase in both samples. Although the InN-OT film has a higher oxygen concentration, both films show similar electrical and optical properties. © 2008 American Institute of Physics.

Phase separation and optical properties in oxygen-rich InN films

We have investigated the ac magnetic susceptibility and magnetic heating of aqueous suspensions of γ- Fe2 O3 nanoparticles embedded in alginate hydrogel matrix and isolated γ- Fe2 O3 and Fe3 O4 nanoparticles coated with tetramethyl ammonium hydroxide. All three ferrofluids were characterized by measuring the dc magnetization, ac susceptibility, and magnetic heating. We found that significant Ńel relaxation is present in all samples, but only the isolated nanoparticle ferrofluids show any significant feature associated with Brownian relaxation near the freezing temperature of the carrier liquid. The heating rate of the ferrofluids varies systematically with the magnitude of the Brownian relaxation peak, despite similar values of the absolute magnetization. These results highlight the importance of the Brownian relaxation for heating applications incorporating magnetic nanoparticles. © 2007 American Institute of Physics.

Magnetic relaxation and dissipative heating in ferrofluids

We consider the teleportation of quantum information consisting of the quantum state of a set S1 of N two-level systems (TLSs), using EPR entangled state consisting of set S2 ⊕ S3 where set S2 has M TLSs and set S3 has N TLSs. The Bell state measurement is done on set S1 ⊕ S2 and a unitary transformation, dependent on this result, on the quantum state of set S 3 generates a replica of the original state of set S1. We show rigorously that the teleportation is possible only if M ≥ N. © World Scientific Publishing Company.