O.D. Jayakumar

The structural and magnetization studies of Co-doped ZnO co-doped with Cu: Synthesized by co-precipitation method

Co- and Cu-doped ZnO of nominal composition Zn0.95Co0.05O and Zn0.94Co0.05Cu0.01O were synthesized by a co-precipitation method in organic media. Rietveld refinement of X-ray diffraction data of the samples annealed at 725 K showed that they are single phase without any secondary phases. DC magnetization measurements of samples with Cu co-doping (Zn0.94Co0.05Cu0.01O) as a function of field at room temperature showed a ferromagnetic signature while the samples without Cu co-doping (Zn0.95Co0.05O) are paramagnetic in nature. Both the samples heated at 1075 K are found to be paramagnetic at room temperature. Resistivity measurements above room temperature clearly showed a semiconducting behavior with a decreased resistivity value for Zn0.94Co0.05Cu0.01O compared to Zn0.95Co0.05O and ZnO, confirming additional carriers in Zn0.94Co0.05Cu0.01O due to Cu co-doping. Our results are in agreement with a recent computational study that doping additional carriers are necessary for realizing room temperature ferromagnetism in Co-doped ZnO.

Preparation, phase transition and thermal expansion studies on low-cristobalite type Al1−xGaxPO4 (x=0.0, 0.20, 0.50, 0.80 and 1.00)

Abstract The orthorhombic (α) low-cristobalite type AlPO4 and GaPO4 and their solid solutions are prepared by co-precipitation followed by high temperature annealing of the precipitate. The single phasic nature of the products is ascertained by powder XRD at room temperature. The high temperature behavior of these samples is studied by HT-XRD over the temperature range of 25–1000°C. All these compositions undergo an orthorhombic to cubic (β, high-cristobalite) phase transition at elevated temperature. The unit cell parameters at different temperatures are determined by refining the observed powder diffraction profiles. The phase transition is accompanied by a significant increase in the unit cell volume, leading to the formation of a low dense structure. The variation of unit cell volume with temperature for each composition shows that the orthorhombic phase has a significantly larger thermal expansion than the cubic (high temperature) phase. The high temperature behavior of all the compositions except the GaPO4 is similar. GaPO4 undergoes a phase separation to a more stable quartz type phase above 800°C. However, the quartz type phase again transforms to the high cristobalite (β) phase at 1000°C. Thermal expansions of all these phases are explained in term of the variation of M–O–P angle as a function of temperature.

Fabrication of flexible and self-standing inorganic–organic three phase magneto-dielectric PVDF based multiferroic nanocomposite films through a small loading of graphene oxide (GO) and Fe3O4 nanoparticles

Flexible inorganic-organic magneto-electric (ME) nanocomposite films (PVDF, PVDF-GO, PVDF-Fe3O4 and PVDF-GO-Fe3O4), composed of well-dispersed graphene oxide (GO 5 wt%) and magnetic Fe3O4 nanoparticles (5 wt%) embedded into a poly(vinylidene-fluoride) (PVDF) matrix, have been prepared by a solvent casting route. The magnetic, ferroelectric, dielectric, magneto-dielectric (MD) coupling and structural properties of these films have been systematically investigated. Magnetic (Ms = 2.21 emu g(-1)) and ferroelectric (P = 0.065 μC cm(-2)) composite films of PVDF-GO-Fe3O4 (PVDF loaded with 5% GO and 5% Fe3O4) with an MD coupling of 0.02% at room temperature (RT) showed a three times higher dielectric constant than that of the pure PVDF film, with a dielectric loss as low as 0.6. However, the PVDF-Fe3O4 film, which exhibited improved magnetic (Ms = 2.5 emu g(-1)) and MD coupling (0.04%) properties at RT with a lower dielectric loss (0.3), exhibited decreased ferroelectric properties (P = 0.06 μC cm(-2)) and dielectric constant compared to the PVDF-GO-Fe3O4 film. MD coupling measurements carried out as a function of temperature on the multi-functional PVDF-GO-Fe3O4 film showed a systematic increase in MD values up to 100 K and a decrease thereafter. The observed magnetic, ferroelectric, dielectric, MD coupling and structural properties of the nanocomposite films are attributed to the homogeneous dispersion and good alignment of Fe3O4 nanoparticles and GO in the PVDF matrix along with a partial conversion of nonpolar α-phase PVDF to polar β-phase. The above multi-functionality of the composite films of PVDF-Fe3O4 and PVDF-GO-Fe3O4 paves the way for their application in smart multiferroic devices.

Piezoelectric inkjet printed films and patterns of ZnO and Mn doped ZnO: formation of bifunctional Zn0.98Mn0.02O films

Films and patterns of ZnO and Zn0.98Mn0.02O semiconductors have been inkjet printed, using their precursor inks, on Si and polyimide substrates with a drop on demand inkjet printer. A Zn0.98Mn0.02O film printed on Si after processing showed enhanced bi-functional properties, like room temperature ferromagnetism and ultraviolet sensing, compared to diamagnetic and the ultraviolet sensing properties of a pristine ZnO film. Thus, this process opens up new possibilities of patterning advanced multifunctional materials.

Hydrogen-induced spin reorientation in TbFe2Hx system

Abstract The hydriding characteristics of cubic C-15 structured TbFe 2 have been studied. It is observed that homogeneously hydrided samples with varying concentrations of hydrogen could be prepared under less than one atmosphere of hydrogen pressure without any activation. The saturation hydride composition achieved is TbFe 2 H 4.8 . All hydrides have been found to be crystalline and retain their cubic character. A temperature and hydrogen concentration dependent spin reorientation has been observed for TbFe 2 H x samples.