Search

A combination of x-ray diffraction, x-ray photoemission and several other techniques is employed to explain the electronic, as well as the magnetic properties of the Co-doped Ti[O.sub.2] polycrystalline pellets. The ferromagnetism induced in the compounds because of the presence of various defects is also analyzed.

The grazing incidence x-ray diffraction (GIXRD), x-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy was used to investigate samples with crystalline [alpha]-[Fe.sub.2][O.sub.3] nanowires grown on pure Fe substrates by controlled thermal oxidation route. The results reveal that analysis of diffraction patterns has shown that bending of nanowires occurs preferentially about the c axis whereas they are stiffer to bend in other direction.

γ-Fe2O3 nanoparticles of ∼100 nm size were prepared through self-propagating combustion route using ferrous phthalate precursor employing polyethylene glycol as a fuel. As prepared γ-Fe2O3 was characterised by employing X-ray diffraction (XRD), scanning electron micrograph (SEM), Mossbauer spectroscopy, energy dispersive X-ray microanalysis (EDAX) and X-ray photoelectron spectroscopy (XPS). From XRD and XPS, we find that the surface of these nanoparticles is α-Fe2O3 and the core is γ-Fe2O3 . γ-Fe2O3 particles were spherical in shape showing a well-resolved 6 narrow bands in Mossbauer spectrum. No impurities were present, as indicated by EDAX and also no other phase than α and γ was present which substantiates suitability of the synthesis route for γ-Fe2O3 nanoparticles. The magnetic properties of the γ-Fe2O3 were also studied by using vibrating sample magnetometer (VSM). [ABSTRACT FROM AUTHOR]

Abstract: We report on the reversible manipulation of room temperature ferromagnetism in Fe (5%) doped In2O3 polycrystalline magnetic semiconductor. The X-ray diffraction and photoemission measurements confirm that the Fe ions are well incorporated into the lattice, substituting the In3+ ions. The magnetization measurements show that the host In2O3 has a diamagnetic ground state, while it shows weak ferromagnetism at 300K upon Fe doping. The as-prepared sample was then sequentially annealed in hydrogen, air, vacuum and finally in air. The ferromagnetic signal shoots up by hydrogenation as well as vacuum annealing and bounces back upon re-annealing the samples in air. The sequence of ferromagnetism shows a close inter-relationship with the behavior of oxygen vacancies (V o). The Fe ions tend to a transform from 3+ to 2+ state during the giant ferromagnetic induction, as revealed by photoemission spectroscopy. A careful characterization of the structure, purity, magnetic, and transport properties confirms that the ferromagnetism is due to neither impurities nor clusters but directly related to the oxygen vacancies. The ferromagnetism can be reversibly controlled by these vacancies while a parallel variation of carrier concentration, as revealed by resistance measurements, appears to be a side effect of the oxygen vacancy variation. [Copyright &y& Elsevier]

Abstract: Influence of Co doping for In in In2O3 matrix has been investigated to study the effect on magnetic vs. electronic properties. Rietveld refinement of X-ray diffraction patterns confirmed formation of single phase cubic bixbyite structure without any parasitic phase. Photoelectron spectroscopy and refinement results further revealed that dopant Co2+ ions are well incorporated at the In3+ sites in In2O3 lattice and also ruled out formation of cluster in the doped samples. Magnetization measurements infer that pure In2O3 is diamagnetic and turns to weak ferromagnetic upon Co doping. Hydrogenation further induces a huge ferromagnetism at 300K that vanishes upon re-heating. Experimental findings confirm the induced ferromagnetism to be intrinsic, and the magnetic moments to be associated with the point defects (oxygen vacancies V o) or bound magnetic polarons around the dopant ions. [ABSTRACT FROM AUTHOR]