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Singh P.,Functional Nanomaterials Research Laboratory | Kaur D.,Functional Nanomaterials Research Laboratory
Physica B: Condensed Matter | Year: 2010

We report, the structural and optical properties of nanocrystalline anatase TiO2 thin films grown on glass substrate by dc magnetron sputtering at room temperature. The influence of sputtering power and pressure over crystallinity and surface morphology of the films were investigated. It was observed that increase in sputtering power activates the TiO2 film growth from relative lower surface free energy to higher surface free energy. XRD pattern revealed the change in preferred orientation from (1 0 1) to (0 0 4) with increase in sputtering power, which is accounted for different surface energy associated with different planes. Microstructure of the films also changes from cauliflower type to columnar type structures with increase in sputtering power. FESEM images of films grown at low pressure and low sputtering power showed typical cauliflower like structure. The optical measurement revealed the systematic variation of the optical constants with deposition parameters. The films are highly transparent with transmission higher than 90% with sharp ultraviolet cut off. The transmittance of these films was found to be influenced by the surface roughness and film thickness. The optical band gap was found to decrease with increase in the sputtering power and pressure. The refractive index of the films was found to vary in the range of 2.50-2.24 with increase in sputtering pressure or sputtering power, resulting in the possibility of producing TiO2 films for device applications with different refractive index, by changing the deposition parameters. © 2009 Elsevier B.V. All rights reserved. Source

Vishnoi R.,Functional Nanomaterials Research Laboratory | Singhal R.,Inter University Accelerator Center | Asokan K.,Inter University Accelerator Center | Kanjilal D.,Inter University Accelerator Center | Kaur D.,Functional Nanomaterials Research Laboratory
Applied Physics A: Materials Science and Processing | Year: 2012

The effects of 200 MeV Au ions irradiation on the structural and magnetic properties of Ni-Mn-Sn ferromagnetic shape memory alloy (FSMA) thin films have been systematically investigated. In order to understand the role of initial microstructure and phase of the film with respect to high energy irradiation, the two types of Ni-Mn-Sn FSMA films having different phases at room temperature were irradiated, one in martensite phase (Ni58.9Mn28.0Sn13.1) and other in austenite phase (Ni 50Mn 35.6Sn 14.4). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images along with the diffraction patterns of X-rays and electrons confirm that martensite phase transforms to austenite phase at a fluence of 6 × 10 12 ions/cm 2 and a complete amorphization occurs at a fluence of 3 × 10 13 ions/cm 2, whereas ion irradiation has a minimal effect on the austenitic structure (Ni 50Mn 35.6Sn 14.4). Thermomagnetic measurements also support the above mentioned behaviour of Ni-Mn-Sn FSMA films with increasing fluence of 200 MeV Au ions. The results are explained on the basis of thermal spike model considering the core and halo regions of ion tracks in FSMA materials. © 2012 Springer-Verlag. Source

Akkera H.S.,Functional Nanomaterials Research Laboratory | Choudhary N.,University of North Texas | Kaur D.,Functional Nanomaterials Research Laboratory
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2015

We systematically investigated the influence of aluminium (Al) content on the martensitic transformations and magnetocaloric effect (MCE) in Ni-Mn-Sb ferromagnetic shape memory alloy (FSMA) thin films. The temperature-dependent magnetization (M-T) and resistance (R-T) results displayed a monotonic increase in martensitic transformation temperature (TM) with increasing Al content. From the isothermal magnetization (M-H) curves, a large magnetic entropy change (ΔSM) of 23 mJ/cm3 K was observed in N49.8Mn32.97Al4.43Sb12.8. A remarkable enhancement of MCE could be attributed to the significant change in the magnetization of Ni-Mn-Sb films with increasing Al content. Furthermore, a high refrigerant capacity (RC) was observed in Ni-Mn-Sb-Al thin films as compared to pure Ni-Mn-Sb. The substitution of Al for Mn in Ni-Mn-Sb thin films with field induced MCE are potential candidates for micro length scale magnetic refrigeration applications where low magnetic fields are desirable. © 2015 Elsevier B.V. All rights reserved. Source

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