Search

Femtosecond laser pulses are used to demonstrate the direct writing of ferromagnetism in hydrogenated [Ga.sub.0.96][Mn.sub.0.04]As. Interruption of the laser beam during writing which leads to the formation of a paramagnetic gap with controllable conductance separating two ferromagnetic line segments along with the laser tunability of magnetic and electrical properties in the activated regions represent a planar approach to defining all-semiconductor spintronic structures for device applications.

The magnetic properties of the isostructural spinel-spinel interface of Ni[Mn.sub.2][O.sub.4] (NMO)-[Fe.sub.3][O.sub.4] are examined. The results have shown that the magnetic properties have come from a thin interdiffused region of [(Fe, Mn, Ni).sub.3][O.sub.4] at the interface, which has led to Mn and Ni magnetic properties similar to those of Mn[Fe.sub.2][O.sub.4] and Ni[Fe.sub.2][O.sub.4].

Chemically sensitive x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) are used for addressing a long standing controversy regarding the electronic and magnetic states of Cu[Cr.sub.2][Se.sub.4] via halogen doping of the Se anion site in Cu[Cr.sub.2][Se.sub.4-x][Y.sub.x] (Y = Cl and Br). XMCD spectra have shown the presence of a magnetic moment associated with the Cu ions that is aligned antiparallel to the Cr moment.

The magnetic and magnetotransport properties of thin films of ferromagnetic [Ga.sub.1-x][Mn.sub.x]As, which is prepared by using ion implantation and pulsed-laser melting (II-PLM), are examined. It is shown that II-PLM [Ga.sub.1-x][Mn.sub.x]As films are free from interstitial [Mn.sub.I] due to the high-temperature processing.

[Fe.sub.3][O.sub.4]/[Mg.sub.2]Ti[O.sub.4] (MTO/[La.sub.0.7][Sr.sub.0.3]Mn[O.sub.4] (LSMO) junctions were fabricated using pulsed layer deposition and characterized. Measurements of the junction magnetoresistrance performed on junctions with barrier thicknesses ranging from 50-120 Angstroms showed that the resistance jumps in junction magnetoresistance (JMR) correspond well to the switching fields of the LSMO and [Fe.sub.3][O.sub.4] magneto electrodes.

Abstract: We report on the successful synthesis, magnetism and transport of highly spin-polarized chalcogenide thin films of CuCr2Se4, which are promising candidates for spin-based electronic applications. We also present electronic structure calculations for CuCr2Se4 that, together with magnetic and transport data, imply that the stoichiometric compound is a metallic ferromagnet with a relatively low density of hole-like carriers at the Fermi energy. These calculations also predict that a deficiency of Se will deplete the minority density of states at the Fermi energy perhaps leading to a half-metal. We have successfully grown thin films of CuCr2Se4 by pulsed laser deposition on isostructural MgAl2O4 substrates followed by an anneal in a Se-rich environment. X-ray diffraction confirms the structure of CuCr2Se4 on MgAl2O4 substrates as well as a secondary phase of Cr2Se3. X-ray absorption spectroscopy indicates that the chemical structure at the surface of the films is similar to that of bulk CuCr2Se4 single crystals. Magnetization measurements indicate that these films saturate with a magnetic moment close to 5 μ B/f.u. and a Curie temperature (T c) above 400K. X-ray magnetic circular dichroism measurements show that magnetic order persists to the surface of the film. Resistivity and Hall effect measurements are consistent with p-type ferromagnetic metallic behavior and with the electronic structure calculations. [Copyright &y& Elsevier]

Abstract: Epitaxial thin films of CaVO3 were synthesized on SrTiO3, LaAlO3 and (La0.27Sr0.73)(Al0.65Ta0.35)O3 substrates by pulsed laser deposition. All CaVO3 films, independent of epitaxial strain, exhibit metallic and Pauli paramagnetic behavior as CaVO3 single crystals. X-ray absorption measurements confirmed the 4+ valence state for Vanadium ions. With prolonged air exposure, an increasing amount of V3+ is detected and is attributed to oxygen loss in the near surface region of the films. [Copyright &y& Elsevier]

Abstract: We demonstrate two patterning techniques based on hydrogen passivation of Ga1− x Mn x As to produce isolated ferromagnetically active regions embedded uniformly in a paramagnetic, insulating host. The first method consists of selective hydrogenation of Ga1− x Mn x As by lithographic masking. Magnetotransport measurements of Hall-bars made in this manner display the characteristic properties of the hole-mediated ferromagnetic phase, which result from good pattern isolation. Arrays of Ga1− x Mn x As dots as small as 250nm across have been realized by this process. The second process consists of blanket hydrogenation of Ga1− x Mn x As followed by local reactivation using confined low-power pulsed-laser annealing. Conductance imaging reveals local electrical reactivation of micrometer-sized regions that accompanies the restoration of ferromagnetism. The spatial resolution achievable with this method can potentially reach <100nm by employing near-field laser processing. The high spatial resolution attainable by hydrogenation patterning enables the development of systems with novel functionalities such as lateral spin-injection as well as the exploration of magnetization dynamics in individual and coupled structures made from this novel class of semiconductors. [Copyright &y& Elsevier]