Monte Carlo simulation studies are performed to examine the implications of octahedral cation (Fe, Mo) site disorder for magnetization in the double-perovskite Sr2FeMoO6. Correlations between the near-neighbor cation distributions and the spin distributions are identified to gain insight into the spin arrangement within, and on the periphery of a given transition element cation cluster. It is shown that the drop in the magnetic moment is nearly linear with the increase in the mis-site defect concentration for the case of randomly created defects. Implications of the concomitant presence of mis-site defects and oxygen vacancies are also analyzed.

Arrays of perpendicular ferromagnetic nanowires have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple approach to create self-assembled nanowires of alpha-Fe through the decomposition of a suitably chosen perovskite. We illustrate the principle behind this approach using the reaction 2La(0.5)Sr(0.5)FeO(3) --> LaSrFeO(4) + Fe + O(2) that occurs during the deposition of La(0.5)Sr(0.5)FeO(3) under reducing conditions. This leads to the spontaneous formation of an array of single-crystalline alpha-Fe nanowires embedded in LaSrFeO(4) matrix, which grow perpendicular to the substrate and span the entire film thickness. The diameter and spacing of the nanowires are controlled directly by deposition temperature. The nanowires show uniaxial anisotropy normal to the film plane and magnetization close to that of bulk alpha-Fe. The high magnetization and sizable coercivity of the nanowires make them desirable for high-density data storage and other magnetic-device applications.

We have investigated the structure and electronic properties of ferrimagnetic double perovskites, A 2 FeReO 6 (A= Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m) and metallic, while the A=Ca phase is monoclinic (P2 1 /n) and nonmetallic. 57 Fe Mossbauer spectroscopy shows that iron is present mainly in the high-spin (S=5/2) Fe 3+ state in the Ca compound, while it occurs in an intermediate state between high-spin Fe 2+ and Fe 3+ in the Ba compound. It is argued that a direct Re t 2g -Re t 2g interaction is the main cause for the metallic character of the Ba compound; the high covalency of Ca-O bonds and the monoclinic distortion (which lifts the degeneracy of t 2g states) seem to disrupt the Re-Re interaction in the case of the Ca compound, making it non-metallic for the same electron count.

Nanoparticles of TiO 2 have been synthesized by an ion beam sputtering-cold condensation (IBS-CC) technique. A sintered TiO 2 was sputtered by an ion beam (Kaufman source, 900 eV, Ar + ions) and the ejected atoms/radicals were made to condense on a Si(100) substrate held at −50 • C. X-ray diffraction data showed that the average particle size in the as-deposited material is about 3.5 ± 1.5 nm. Upon annealing at 600 • C for five hours, the average particle size was seen to increase to about 70 ± 10 nm. Further annealing for one hour at 900 • C led to increase of average particle size to 200 ± 20 nm. X-ray spectroscopy, Raman spectroscopy and photoluminescence data have been used to reveal the presence and relative concentrations of rutile and anatase phases of TiO 2 in the as-deposited and annealed samples. The IBS-CC method is found to yield a more compact particle size distribution as compared to the method based on Laser Ablation.

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In this letter, we report the thermal processing controlled tunability of localized surface plasmon resonance (LSPR) of Au nanoparticles embedded in ZnO matrix. Au–ZnO nanocomposite films were prepared by atom beam cosputtering and were annealed from 200to600°C in Ar. A regular redshift ∼110nm (from 505to615nm) in LSPR peak with increase in annealing temperature up to 600°C is observed. Transmission electron microscopy results confirm the formation of Au nanoparticles supported by ZnO nanorods at annealing temperature of 600°C. The Au–ZnO nanocomposite exhibits significant enhancement in the Raman signal for C70 molecules.

The development of self-assembled magnetic CoFe 2 O 4 nanoparticles within polymer matrices at room temperature is reported. Diblock copolymers consisting of poly ͑norbornene͒ and poly ͑norbornene-dicarboxcylic acid͒ ͑NOR/NORCOOH͒ were synthesized. The self-assembly of the mixed metal oxide within the NORCOOH block was achieved at room temperature by processing the copolymer nanocomposite using wet chemical methods. Morphology and magnetic properties were determined by superconducting quantum interference device magnetometry, transmission electron microscopy, wide angle x-ray diffraction, and 57 Fe Mössbauer spectroscopy. The CoFe 2 O 4 nanoparticles are uniformly dispersed within the polymer matrix, and have an average radius of 4.8Ϯ1.4 nm. The nanocomposite films are superparamagnetic at room temperature and ferrimagnetic at 5 K.

Growth of MgB2 thin films by pulsed laser deposition is examined under ex situ and in situ processing conditions. For the ex situ process, Boron films grown by PLD were annealed at 900 C with excess Mg. For the in situ process, different approaches involving ablation from a stoichiometric target under different growth conditions, as well as multilayer deposition involving interposed Mg layers were examined and analyzed. Magnetic measurements on ex situ processed films show TC of ~39 K, while the current best in situ films show a susceptibility transition at ~ 22 K.Comment: 3 pages, PD