Magnetic nanoparticles of cobalt ferrite have been synthesized by wet chemical method using stable ferric and cobalt salts with oleic acid as the surfactant. X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) confirmed the formation of single phase cobalt ferrite nanoparticles in the range 15-48nm depending on the annealing temperature and time. The size of the particles increases with annealing temperature and time while the coercivity goes through a maximum, peaking at around 28nm. A very large coercivity (10.5kOe) is observed on cooling down to 77K while typical blocking effects are observed below about 260K. The high field moment is observed to be small for smaller particles and approaches the bulk value for large particles. PACS: 75.50Gg; 75.50Tt; 75.70Rf

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

Hollow NiFe2O4 nanoparticles are synthesized by self-templating process utilizing coupled interfacial chemical reactions and Kirkendall effect between the core (Ni33Fe67) and the shell (NiFe2O4) of the core/shell structure. Reaction temperature and time dependent structural and morphogical transformations are presented in detail. The kinetics of the transformation from (Ni33Fe67)/(NiFe2O4) nanoparticles to single phased NiFe2O4 hollow nanoparticles was studied by differential scanning calorimetry. Hollow morphology of the particles induces surface effects in the magnetic properties due to the formation of additional inner surfaces. Field cooled hysteresis loop exhibits significantly large shift due to unidirectional anisotropy resulting from the additional inner spin disordered surface along with the existing outer spin disordered surface. The enhancement in the surface anisotropy is also noticeable which leads to an increase in the blocking temperature of the particles with hollow morphology.

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