Investigation of dark and light conductivities in calcium doped bismuth ferrite thin films

Electrical conductivities in dark and light were investigated in Calcium doped Bismuth Ferrite thin films. Higher dark conductivity, in the order of 10 times higher than conductivity of bismuth ferrite, was observed for Bi_0.85Ca_0.15FeO_3 ? δ. Structural analyses using Rietveld refinement showed a deviation from volume reduction for Bi_0.85Ca_0.15FeO_3 ? δ which could be the reason of abnormally high conductivity for this compound. Although higher calcium doping reduced conductivity, photoconductivity was observed again. Atomic Force Microscopy investigations showed that surface roughness and grain size decreased with increasing calcium concentration. Enhanced photoconductivity is reported for Bi_0.7Ca_0.3FeO_3 ? δ with ~ 2.8 eV direct optical band gap at 300 K with surface roughness of ~ 2 nm.     

Saturation magnetostriction measurements of magnetic thin films under high magnetic fields

Saturation magnetostriction measurements of magnetic thin films have been studied using a system equipped with a motor driven electromagnet and a laser displacement meter. A new method to reduce the errors caused by applied rotating magnetic field is proposed for high-sensitive and accurate measurements of saturation magnetostriction. It is shown that accurate measurements are possible for magnetic fields up to around 1 kOe, by extracting the 2nd harmonic output through Fourier analysis as a function of applied rotating magnetic field and then by taking the extrapolation of 2nd harmonic output to zero magnetic field. This method is applied to measure a saturation magnetostriction of single-crystal fcc-Co(111) film and the value of − 30 × 10^− 6 is obtained.     

The binding energy of molecules in thin fullerene films

Thin fullerene films formed using the methods of pulsed supersonic molecular beam (SMB) deposition and thermal deposition (TD) in vacuum were studied by thermodesorption (TDS) mass spectroscopy. The TDS spectra of SMB films show a significantly higher temperature of desorption (827.8 K) of fullerene molecules as compared to the value (583 K) observed in the spectra of TD films. It is suggested that the higher binding energies of fullerene molecules in the former films are explained by the formation of polymer structures due to heating in the course of TDS measurements.     

Induced magnetic anisotropy and strain in permalloy films deposited under magnetic field

Field induced magnetic-anisotropy is a very important but poorly understood property. There have been many hypotheses on the origin of the phenomenon, e.g. strain, atomic pair ordering, etc., but little experimental evidence exist. This study prepares 100 nm thick Permalloy films having the field-induced-magnetic-anisotropy and carefully measure strains, i.e. interplanar distance of crystallographic (111) planes in various directions, using high power synchrotron radiation and precise Grazing Incidence X-Ray Diffraction method. The result delineates that the field-induced-magnetic-anisotropy has a strong correlation with the strain-anisotropy in the film.     

Conduction and dielectric polarization in Se thin films

Se films were prepared by thermal evaporation technique in thickness range 150-8500 Å. X-ray diffraction measurements showed that Se films are in the amorphous state. The ac conductivity and dielectric properties of the amorphous Se films have been investigated in the frequency range 100-100 KHz and 100-400 K temperature range. The ac conductivity σ_ac(ω) is found to be proportional to ω^s where s<1. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier (CBH) model. The dc conductivity at the room temperature was also studied in the same thickness range. It was concluded that the same mechanism of carrier motion might be dominant in both ac polarization and dc conduction. This carrier transport mechanism might be electronic.     

The measurement of the anisotropy field of cylindrical thin magnetic films

The described method for the anisotropy field measurement uses two fields HLand HT. The deviation of magnetization from the easy direction, and hence also sense signals, are proportional to these fields. The ratio of two integrated sense signals atH_{L} = 0andH_{L} neq 0reaches a certain value (∼ 2.5) with fieldH_{T} = H_{k}. In this way, Hkmay be measured by a device designed for the coercive force measurement.     

Flexoelectric rotation of polarization in ferroelectric thin films

Strain engineering enables modification of the properties of thin films using the stress from the substrates on which they are grown. Strain may be relaxed, however, and this can also modify the properties thanks to the coupling between strain gradient and polarization known as flexoelectricity. Here we have studied the strain distribution inside epitaxial films of the archetypal ferroelectric PbTiO(3), where the mismatch with the substrate is relaxed through the formation of domains (twins). Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal an intricate strain distribution, with gradients in both the vertical and, unexpectedly, the horizontal direction. These gradients generate a horizontal flexoelectricity that forces the spontaneous polarization to rotate away from the normal. Polar rotations are a characteristic of compositionally engineered morphotropic phase boundary ferroelectrics with high piezoelectricity; flexoelectricity provides an alternative route for generating such rotations in standard ferroelectrics using purely physical means.     

Temperature-dependent photoluminescence of thin tetraphenylporphyrin-based thin films and their composites with C60 fullerene

Journal of Materials Science: Materials in Electronics - The investigation of the temperature effect on optical properties of porphyrins has tremendous impact for modern organic-based photonics and...     

The magnetic field effect on optical properties of Sm-doped GaN thin films

We report the optical and magnetic properties of Sm doped wide-band-gap Gallium nitride (GaN) prepared by ion implantation. The photoluminescence (PL) intensity obviously increased as the increasing of annealing temperature from 700 to 1,100 °C. Magnetic hysteresis was observed at room temperature. Our study was focusing on the influence of magnetic field on optical property of Sm³⁺ doped GaN. It was discovered that the PL intensity of Sm³⁺ increases remarkably under an external magnetic field. The mechanism of the magnetic ordering-modulated PL peak intensity of Sm³⁺ doped GaN films was discussed. This may open up a suite of potential applications in producing magneto-optical devices.     

Pulse switching in thin magnetic films

The main results of the investigations of pulse switching in thin magnetic films with uniaxial anisotropy which have been obtained in Moscow State University are reviewed. Simultaneous investigation of integral switching properties, inner effective field, and dynamic domains produced during pulse switching has increased our understanding of bi-directional incoherent rotation mechanism and found new peculiarities of the pulse switching by domain boundary propagation. A new variety of incoherent rotation which manifests itself at strong fields has been found. It has been also found that the curve representing the pulse field dependence of an inverse switching time in the general case consists of five distinct regions. The relation between these regions and the switching mechanisms are discussed.     

Charged walls in thin magnetic films

Charged walls are domain walls which carry a net "magnetic charge" (div M) due to their orientation relative to the domain magnetizations. They differ from ordinary Bloch and Néel walls (which are uncharged) primarily in their much wider profile. In order to calculate such walls, a variational method was developed. It is based on the separation of that part of stray field energy which would be present even with an infinitely thin wall. The main results of the calculations are as follows. 1) Isolated charged walls do exist if exchange energy is taken into account, as opposed to the periodic solution known for the limit of negligible exchange energy. 2) Rotated, partially charged walls develop a Néel-wall-like narrow core region. Detailed results for the wall profiles, energies and widths as a function of wall angle, orientation, film thickness, and material parameters are presented. They are applied to two examples: the case of a Permalloy film in a domain tip propagation memory, and the case of the implanted layer on a contiguous disk bubble device.     

Scattering and polarization of light by magnetic fluids

Expression for the intensity and the degree of polarization of light scattered by a magnetic colloid are derived. Experimental results obtained by earlier investigators are discussed on the basis of these expressions.     

Ferrofluid thin films as optical gaussmeters proposed for field and magnetic moment sensing

Ferrofluids belonging to the series, Ni _x Fe_1-x Fe₂O₄ and Zn _x Fe_1-x Fe₂O₄, were synthesized using cold co-precipitation. Liquid films of these ferrofluids were prepared by encapsulating the ferrofluids in between two optically smooth and ultrasonically cleaned glass plates. Magnetic field induced laser transmission through these ferrofluid films has been investigated. Magnetic field values can be calibrated in terms of output laser power in the low field region in which the variation is linear. This set up can be used as a cheap optical gaussmeter in the low field regime. Using the same set-up, the saturation magnetization of the sample used can also be calculated with a sample that is pre-characterized. Hence both magnetization of the sample, as well as applied magnetic field can be sensed and calculated with a precalibrated sample.     

Electron structure of thin fullerene films deposited by various methods

The valence-band photoelectron spectra and the photoelectron energy loss spectra behind the C1s peak in the X-ray photoelectron spectra were studied in thin fullerene films deposited by various methods. The fine structure in the density of states near the valence band bottom observed for the fullerene films deposited by the method of pulsed supersonic molecular beam (SMB) with a helium carrier may be indicative of the presence of a long-range order. The spectra of π-plasmon losses in the films obtained by methods of thermal and SMB deposition exhibit a significant difference that can be related to a closer packing of C₆₀ molecules in the latter case.     

Conduction and dielectric polarization in thin anodic aluminium oxide films

The a.c. polarization of anodic Al₂O₃ films was studied in the thickness range 30–1500 Å and the frequency range 300 Hz to 15 kHz. The interfacial polarization mechanism involving distinct regions separated by flaws and/or voids in the bulk was thought to become dominant with decreasing thickness because of an increasing concentration of defects. The d.c. conductivity at the room temperature was also studied in the same thickness range. The observed linear log J versus E^1/2 characteristics for several thicknesses showed that d.c. conduction in these films obeys the Poole-Frenkel law over a certain range of applied electric fields. Anomalies observed in the electric field and the thickness dependences of the d.c. conductivity are considered to arise from the thickness dependence of the defect concentration. It was concluded that the same mechanism of carrier motion might be dominant in both a.c. polarization and d.c. conduction.     

Dynamic scaling function of polarization hysteresis in ferroelectric thin films

The scaling behavior of the polarization hysteresis dispersion in a mode spin-like system based on the three-dimensional (Φ²)² model with O(N) symmetry in the limit N → ∞, upon applying of the time-varying electric field, is investigated. We perform a simple analysis on the dynamic relaxation of the polarization and propose a scaling function in order to describe the scalability of the hysteresis dispersions over a wide range of field magnitude. The applicability of this scaling function is demonstrated by a consistent fitting to the experimental data on several types of ferroelectric thin films.     

Magnetochromatic effects in magnetic fluid thin films

A homogeneous ferrofluid composition capable of reversiblyforming ordered crystalline two-dimensional hexagonal lattices ofmagnetic particle columns in a thin film under the influence ofexternal magnetic fields has been synthesized. We can manipulatethe spacings between the particles columns by adjusting parameters suchas external magnetic field strength, film thickness, rate of change ofthe field strength, and concentration of magnetic particles in theferrofluid. These spacings between particle columns are of theorder of several micrometers and are capable of diffracting visiblelight to produce monochromatic interference colors. We can changethe resulting colors by altering the lattice spacing to exhibit thefeasibility of generating monochromatic colors.     

Control of magnetic properties in metallo-organic thin films

Magnetic metallo-organic thin films have been prepared at different growth temperatures to characterize the influence of structural properties on the magnetic characteristics. A quantitative analysis of the grain size shows that the growth temperature increases the elliptical grain size considerably. Long grains of planar iron phthalocyanine form quasi one-dimensional iron chains, which are embedded in a carbon matrix along the other two dimensions. The chains are narrowly spaced (1.3 nm) and run parallel to the substrate. Temperature-dependent magnetization curves depend on the structural details of the iron chains. These magnetic properties are tuned with deposition parameters.