Samta Chauhan

Zero-field cooled exchange bias in hexagonal YMnO3 nanoparticles

Effect of varying particle size and maximum applied field during initial magnetization (HM) on zero-field cooled (ZFC) exchange bias (EB) in hexagonal YMnO3 nanoparticles prepared by conventional solid state method has been studied. EB phenomenon is observed after ZFC from an unmagnetized state without any remanent magnetization. EB field (Heb) and Vertical shift (ME) were found to vary nonmonotonically with both particle size and HM. Large Heb of 1024 Oe is obtained for the particle size of 55 nm. These features are attributed to the exchange interaction between the compensated antiferromagnetic spins and uncompensated surface spins of the nanoparticles.

Hydrogen sensing properties of nanostructured Pd/WO3 thin films: role of hydrophobicity during recovery process

In the present work the structural, optical and hydrogen sensing properties of Pd-capped tungsten oxide (Pd/WO3) thin films have been investigated. The nanostructured Pd/WO3 thin films have been prepared using DC magnetron sputtering on glass and Si(100) substrates at various oxygen partial pressures. The samples were hydrogenated at 2 bar hydrogen pressure in an operating temperature range 300–423 K. Optical transmittance spectra confirms fully transparent WO3 thin films deposited at oxygen partial pressure of 0.5 Pa while the transmittance drastically decreases to 50% for hydrogenated Pd/WO3 thin films. The influence of surface roughness and hydrophobicity of the Pd/WO3 thin films on the hydrogen sensing performance have been studied. Fast response time (1 sec) and an optimum recovery time (~8 min) have been observed at a moderate temperature of 323 K for the samples having roughness ~4.5 nm and contact angle ~96°. Hydrophobicity of the surface provides short recovery time by opposing the existence of water-vapour on the surface.

Determination of optical constants including surface characteristics of optically thick nanostructured Ti films: analyzed by spectroscopic ellipsometry

In the present work, optically thick nanostructured titanium (Ti) films of thickness ranging from ∼100 to 900 nm were deposited on a glass substrate by DC magnetron sputtering at room temperature. Microstructural and surface properties of the samples were studied by x-ray diffraction and x-ray photoelectron spectroscopy (XPS). The morphological results revealed a systematic normal grain growth mechanism with increasing thickness analyzed by a scanning electron microscope. The influence of thickness on film surface roughness has been investigated by atomic force microscopy (AFM). The optical dispersion behavior was examined by spectroscopic ellipsometry (SE) over the long wavelength range of 246-1688 nm. The experimentally observed SE parameters were theoretically fitted with Drude-Lorentz and Bruggeman effective medium approximation theory. The surface properties of the Ti film measured by XPS and AFM were further accounted for in the optical model to determine optical constants (n and k) and the obtained results are expected to be the best available for bulk Ti metal.

Antisite disorder induced spin glass and exchange bias effect in Nd2NiMnO6 epitaxial thin film

We report the observation of the exchange bias effect and spin glass behaviour at low temperature in a ferromagnetic Nd2NiMnO6 epitaxial thin film. Along with the ferromagnetic transition at ∼194 K, an additional transition is observed at lower temperature (∼55 K) as seen from M-T curves of the sample. A shift in the ac susceptibility peak with frequency has been observed at low temperature, which is a signature of a glassy phase within the sample. The detailed investigation of the memory effect and time dependent magnetic relaxation measurements reveals the presence of a spin glass phase in the Nd2NiMnO6 thin film. The exchange bias effect observed at low temperature in the sample has been associated with an antisite disorder induced spin glass phase, which results in a ferromagnetic/spin glass interface at low temperature. The exchange bias behaviour has been further confirmed by performing cooling field and temperature dependence of exchange bias along with training effect measurements.

Study on structural, optical and wettable properties of CeO2 thin films deposited by reactive DC magnetron sputtering

CeO2 thin films have been deposited on different substrates (Si & quartz) by reactive DC magnetron sputtering technique and effect of target-substrate distance (dT-S) on structural, optical, and wettable properties has been investigated. XRD data reveals that CeO2 films are polycrystalline in nature with cubic structure. Variation in growth rates of different orientations with change in dT-S has been observed. Evolution of (200) peak for the film deposited on Si substrate confirms the substrate dependence of the texture. Surface morphology of the films has been characterized by AFM. Wettability and optical properties have been studied using contact angle goniometer and UV-Vis spectrophotometer, respectively. CeO2 films deposited at 5 cm dT-S have least transmittacnce but highest hydrophobicity among all the studied samples.