Shahid Atiq

Effect of epitaxy and lattice mismatch on saturation magnetization of γ′-Fe4N thin films

We report the effect of epitaxial growth and lattice mismatch on the enhancement of saturation magnetization (Ms) of ferromagnetic γ′-Fe4N thin films deposited on different single crystal substrates having lattice mismatches from 0% to 11%. It was found that Ms in the γ′-Fe4N film increased with increasing degree of epitaxy and minimizing lattice mismatch between the film and the substrate. Maximum saturation magnetization of 1980±20emu∕cm3 (about 24% higher than previous result) was obtained with LaAlO3(100) substrate having zero lattice mismatch after postannealing of 30min, which is believed to originate from magnetovolume effect in well-ordered epitaxially grown films.

Enhanced magnetization of sol-gel synthesized Pb-doped strontium hexaferrites nanocrystallites at low temperature

Effect of Pb doping on the structural and low temperature magnetic properties of SrPbxFe12-xO19 (x = 0, 0.1, 0.2, 0.3, and 0.4), synthesized by sol-gel autocombustion technique, has been investigated. The powder samples were sintered at 800°C for 2 h in order to develop the stable hexagonal phase, characteristic of the SrFe12O19 structure. The consequences of Pb substitution (at iron sites) on various structural parameters like lattice constants, unit cell volume, crystallite size, and porosity have been discussed. Fourier transform infrared frequency bands were utilized to determine the formation of tetrahedral and octahedral clusters of M-type ferrites. Hexagonal texture of the grains, a characteristic of the hexagonal crystal structure of SrFe12O19, was refined by Pb substitution. The magnetic properties, determined using a vibrating sample magnetometer, revealed that saturation magnetization decreased, while coercivity was increased with the increase of Pb contents. However, the increased squareness ratio and hence the energy product motivate the utilization of these ferrite compositions where hard magnetic characteristics are required.The increased values of saturation magnetization were observed at reduced temperature of 200 K, attributable to the better spin alignments of individual magnetic moments at low temperature.

Room Temperature Magnetic Behavior of Sol-Gel Synthesized Mn Doped ZnO

Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto-combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X-ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Temperature dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magnetometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO.

Effect of Co substitution on the structural, electrical, and magnetic properties of Bi0.9La0.1FeO3 by sol-gel synthesis

Cobalt (Co)-doped Bi0.9La0.1FeO3 multiferroics were synthesized by a sol-gel method based on the autocombustion technique. As-synthesized powder was examined using various characterization techniques to explore the effect of Co substitution on the properties of Bi0.9La0.1FeO3. X-ray diffraction reveals that Co-doped Bi0.9La0.1FeO3 preserves the perovskite-type rhombohedral structure of BiFeO3, and the composition without Co preserves the original structure of the phase; however, a second-phase Bi2Fe4O9 has been identified in all other compositions. Surface morphological studies were performed by scanning electron microscopy. Temperature-dependent resistivity of the samples reveals the characteristic insulating behavior of the multiferroic material. The resistivity is found to decrease with the increase both in temperature and Co content. Room temperature frequency-dependent dielectric measurements were also reported. Magnetic measurements show the enhancement in magnetization with the increase in Co content.

Effect of Solvents on the Ferromagnetic Behavior of Undoped BiFeO 3 Prepared by Sol-Gel

We here report the preparation of undoped BiFeO3 (BFO) thin films with sol-gel method using two solvents, i.e., acetic acid (AA) and ethylene glycol (EG). Films are annealed in the temperature range 100-300 °C for 60 mins. Films deposited using AA show the presence of bismuth rich phase Bi46Fe2O72 along with BFO in the intermediary conditions. Pure phase BFO is obtained when films are deposited using EG as a solvent even under as-deposited conditions, and the pure phase persists after annealing in the temperature range 100 °C-300 °C. This is the lowest temperature reported for the preparation of phase pure BFO. Bandgap of AA-based films lies in the range 2.58-2.64 eV and that of EG-based films in the range 2.77-2.81 eV. Reduced value of dielectric constant, in AA-based films, is because of the presence of bismuth rich impurity phase as compared with the films prepared using EG. Bands in FTIR spectra at 487 and 552 cm-1 are characteristic bands of FeO6 and BiO6 groups, indicating the formation of BFO. Films deposited using AA show weak ferromagnetic behavior, while those deposited using EG show strong ferromagnetic behavior as opposed to antiferromagnetic nature of BFO, due to suppression of spiral spin structure.

Multiferroicity in sol–gel synthesized Sr/Mn co-doped BiFeO3 nanoparticles

A simple and cost effective sol–gel auto-combustion technique was used to synthesize Bi0.9Sr0.1Fe1−xMnxO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) multiferroics. Rietveld’s refined X-ray diffraction patterns validated the synthesis of pure phase bismuth ferrite nanoparticles adopting a rhombohedrally distorted ABO3 type perovskite structure with space group R3c. Morphology of the prepared samples manifested the improved crystallinity with increasing Mn contents in BiFeO3. Uniformly distributed multi-shaped grains having varying sizes were formed after combustion which would affect the microstructural related properties of the parent compound. Energy dispersive X-ray spectroscopy confirmed the presence of the relevant elements in the prepared compositions according to their stoichiometric ratio. Enhanced saturation magnetization was observed with increasing doping concentration in the parent compound. Improved polarization versus electric field loops were observed in Mn and Sr co-doped BiFeO3 nanoparticles. All the properties in the present research work have been explained on the basis of dopants and their concentrations, phase purity, microstructure and grain sizes.

Structural, Magnetic, and Electrical Properties of Al3+ Substituted CuZn-ferrites

Nanocrystalline Cu0.5Zn0.5AlxFe2−xO2 (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) ferrite materials were synthesized using standard solid state reaction technique. The effects of Al3+ contents on the structural, electrical, and magnetic properties were investigated. Single phase cubic spinel structure was revealed by X-ray diffraction analysis. The crystallite size was evaluated considering the most intense diffraction peak (311) using Scherrer formula. Lattice constant decreased, whereas porosity increased with the increase in Al3+ concentration. The value of saturation magnetization decreased with increasing aluminum contents. Temperature dependent value of direct current electrical resistivity has been determined. It is observed that the substitution of Al3+ has significant impact on the dielectric constant, tangent of dielectric loss angle and dielectric loss factor. The variation in dielectric properties was attributed to space charge polarization.

Origin of Ferromagnetism in Al and Ni Co-doped ZnO Based DMS Materials

Zn0.95Ni0.05O and Zn0.90Ni0.05Al0.05O compositions of nanocrystallites are synthesised using the well recognised auto-combustion technique. The x-ray diffraction patterns demonstrate the phase pure characteristic wurtzite-type crystal structure with space group P63mc in both the compositions. The elemental incorporation of Ni and Al contents into the ZnO structure is confirmed by energy dispersive x-ray analysis. The micrographs of scanning electron microscopy show an approximate ordered morphology. The electrical resistivity is observed to decrease with the rising temperature, depicting the characteristic semiconductor behaviour of the samples. The lower values of resistivity and ferromagnetic interactions in the Al-doped sample correspond to an increase of carriers density. It is observed that the carrier mediated mechanism is mainly responsible for ferromagnetism in ZnO-based diluted magnetic semiconductors.

Structural and Magnetic Studies of Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O

Single-phase Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O samples were prepared by a novel combustion method. X-ray diffraction studies exhibit the pure phase wurtzite structure of doped ZnO. Energy dispersive x-ray analysis confirms the incorporation of dopants into the host material. Scanning electron microscopy shows the ordered morphology in both of the samples. Temperature-dependent resistivity analysis describes the expected semiconducting behavior that is similar to the parent ZnO materials. Room-temperature magnetic measurements reveal the absence of ferromagnetism in Co-doped ZnO, while the Co and Al co-doped sample displays apparent room-temperature ferromagnetic behavior. The decrease of resistivity and presence of ferromagnetic behavior in Al-doped ZnCoO system corroborate the significant role of free carriers.

Study the structure and performance of thermal/plasma modified Au nanoparticle-doped TiO2 photocatalyst

This study describes the influence of thermal/plasma treatments on the structure and photocatalytic performance of the Au-doped TiO2 catalyst. Au (gold) nanoparticles were attached on TiO2 (Titania) nanoparticle surfaces by conventional deposition precipitation technique and the resulting catalysts were subsequently modified with thermal (at 450 ◦ C under vacuum) and plasma (at an ambient temperature under Argon atmosphere for 20 min) treatments. Structural characterization of the modified catalysts was performed by diverse analytical techniques and the photocatalytic activity was evaluated by assessing the degradation of the methylene blue (MB) in water under UV (ultra-violet) irradiations. Results showed that the thermal/plasma treatment significantly influenced the structural features of Au-doped TiO2 catalyst by altering the morphology, increasing the Au nanoparticles population, improving the Au/TiO2 catalytic activity, changing the textural properties and reducing the band gap energies thus tuned Au-doped TiO2 catalyst to higher efficiency. Thermal/plasma treated Au-doped TiO2 was found to exhibit higher photocatalytic activity than the as-synthesized (pristine sample). This improvement in photocatalytic activity might be due to the cathodic influence of gold in suppressing the electron–hole recombination during the reaction.