Room temperature ferromagnetism is observed in undoped TiO2 films deposited on Si substrates using pulsed laser deposition (PLD). The ferromagnetic properties of the samples depend on the oxygen partial pressure during the PLD synthesis. The appearance of higher binding energy component (HBEC) in the oxygen 1s core peak from x-ray photoelectron spectroscopy (XPS) suggests the presence of oxygen vacancies in these samples. The amount of oxygen during the synthesis determines the vacancy concentration in the samples which is directly related to the magnetic behavior of the samples. The magnetic moment decreases with oxygen vacancy concentration in the samples. Valence band measurements were performed to study the electronic structure of both stoichometric and reduced TiO2. The analyses show the presence of Ti 3d band near the Fermi level in reduced TiO2 samples. These bands are otherwise empty in stoichiometric TiO2 and reside in the conduction band which makes them unobservable by XPS. The existence of this Ti 3d band near the Fermi level can possibly lead to Stoner splitting of the band.Comment: 20 pages, 9 figur

Room temperature ferromagnetism in polycrystalline Co(x)Ce(1-x)O(2-δ) (0.001≤x≤0.10) bulk samples has been investigated. Annealing in the forming gas transformed the as-prepared paramagnetic into a ferromagnetic insulating material with over two orders of magnitude enhancement (from 3.7 × 10(-2) to 1.24 μ(B)/Co) in the magnetization. Structural characterization of both the as-prepared and H(2)-treated samples showed a single phase material. The incorporation of Co with the formation of oxygen vacancies in the oxide lattice was revealed by x-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies is indicated by the existence of mixed valence states of cerium (Ce(4+) and Ce(3+)) in the high resolution XPS 3d spectrum. The role of the donor defects (oxygen vacancies) has been verified through the removal of oxygen vacancies. The ferromagnetic insulating ground state has been explained in terms of the interaction of the F(+) center and 3d magnetic cations. The connection between magnetic properties, electronic structure of the magnetic impurity and donor defect has been established. First principle calculations have been performed using the full potential linearized augmented plane wave method within the density functional theory (DFT) framework; these support our experimental findings. Both the experiment and calculations reinforced the crucial role of oxygen vacancies.

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A simple procedure has been developed for preparing high aspect ratio nanotubes of α-Fe2O3 and Co3O4 with diameters less than 100 nm and wall thicknesses less than 25 nm based on an appropriate heat treatment of electrospun polymeric fibers containing Fe(III) and Co(II) ions. The transformation of the as-prepared nanofibers to the final nanotube structure has been studied by scanning and transmission electron microscopy as well as X-ray diffraction, differential scanning calorimetry/thermogravimetric, and X-ray photoelectron spectroscopy measurements. These measurements and comprehensive analysis have led to a semiquantitative picture of a new nanotube formation mechanism. On the basis of the principles established in this article, it is foreseeable that many other oxide nanotubes could be designed and fabricated, opening a broad avenue to investigate electrical, chemical, mechanical, and magnetic properties. In this particular case, we have shown that magnetic properties are very different between α-Fe2O3 nanofibers and nanotubes, and they are distinctly different from their bulk counterpart.

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In the present study, reactive powder concrete (RPC) was investigated with three different types of single fibers that is, steel fiber (SF), glass fiber (GF), and carbon fiber (CF). Moreover, the effect of hybrid SF‐GF, GF‐CF, and CF‐SF on RPC was also investigated. In case of both single and hybrid fiber‐reinforced RPCs, a constant volume fraction of 2% fiber was used. A plain RPC was also produced that served as a reference/control mix. Studied parameters include compressive strength, modulus of elasticity, peak strains in compression, compression toughness, total energy absorbed in compression, splitting tensile strength, and flexural strength. Results showed that among single fiber‐reinforced RPCs, CF‐RPC performed better than both SF‐ and GF‐RPC in compression. Whereas, single SF‐RPC performed better than GF‐ and CF‐RPC in splitting tensile and flexural strength, single SF‐RPC showed significant softening response compared with single CF and GF‐RPC. CF‐RPC showed comparable performance to that of the SF‐RPC in both tensile and flexural strength. But CF‐RPC showed lower toughness than SF‐RPC. Hybridization of 1%SF and 1%CF yielded maximum overall mechanical performance among both single and hybrid fiber RPCs. Maximum attribution (17–38%) of fibers was toward flexural strength compared to other strength properties.