Vertical spinal electronic device with large room temperature magnetoresistance

We report experimental transport measurements of a vertical hybrid ferromagnetic (FM)/III-V semiconductor (SC)/ferromagnetic(FM) type structure, i.e., Cr(20ML)/Co(15ML)/GaAs(50 nm, n-type)/Al/sub 0.3/Ga/sub 0.7/As(200 nm, n-type)/FeNi(30 nm). The current-voltage (I-V) characteristics reveal Schottky/tunneling type behavior in the direction of FeNi/Semiconductor/Co and observed to be dependent on external magnetic field. The magnetoresistance (MR) behavior shows a strong dependence on the measured current and field. At low fields no significant change in MR has been observed with increasing current. However, at high fields the MR initially increases with increasing current and becomes stable beyond a critical current of 10 /spl mu/A. A maximum of 12% change in the MR has been observed at room temperature, which is far larger than that of the conventional AMR effect. This property of the device could be utilized as field sensors or magnetic logic devices

Transitions in synchronization states of model cilia through basal-connection coupling

Despite evidence for a hydrodynamic origin of flagellar synchronization between different eukaryotic cells, recent experiments have shown that in single multi-flagellated organisms, coordination hinges instead on direct basal body connections. The mechanism by which these connections leads to coordination, however, is currently not understood. Here we focus on the model biflagellate {\it Chlamydomonas reinhardtii}, and propose a minimal model for the synchronization of its two flagella as a result of both hydrodynamic and direct mechanical coupling. A spectrum of different types of coordination can be selected, depending on small changes in the stiffness of intracellular couplings. These include prolonged in-phase and anti-phase synchronization, as well as a range of multistable states induced by spontaneous symmetry breaking of the system. Linking synchrony to intracellular stiffness could lead to the use of flagellar dynamics as a probe for the mechanical state of the cell.Comment: 14 pages, 9 figure

Mesoscovic magnetic/semiconductor heterostructures

We report the experimental results of Fe and Fe3O4 nanostructures on GaAs(100) surfaces and hybrid Ferromagnetic/Semiconductor/Ferromagnetic (FM/SC/FM) spintronic devices. Element specific x-ray magnetic circular dichroism (XMCD) measurements have shown directly that Fe atoms on the GaAs(100)-4 x 6 surface are ferromagnetic. Within coverages of 2.5 to 4.8 ML superparamagnetic nanoclusters are formed and exhibiting strong uniaxial anisotropy, of the order of 6.0 x 10(5) erg/cm(3). The coercivities of epitaxial Fe dot arrays films grown on GaAs(100) were observed to be dependent on the separation and size of the dots indicating that interdot dipolar coupling affects the magnetization processes in these dots. In addition Fe3O4 films grown on deformed GaAs(100) substrates have been observed to form nanostripes following the topography of the substrate and magneto-optical Kerr effect (MOKE) measurements showed that these nanostripes have uniaxial magnetic anisotropy with easy axis perpendicular to the length of the nanostripes. Meanwhile the FM/SC/FM vertical device has exhibited a biasing current dependent on MR characteristics, with a maximum change of 12% in the MR observed, indicating for the first time a large room temperature spin injection and detection

Spin and orbital moments of ultra-thin Fe films on various semiconductor surfaces

The magnetic moments of ultrathin Fe films on three different III-V semiconductor substrates, namely GaAs, InAs and In0.2Ga0.8As have been measured with X-ray magnetic circular dichroism at room temperature to assess their relative merits as combinations suitable for next-generation spintronic devices. The results revealed rather similar spin moments and orbital moments for the three systems, suggesting the relationship between film and semiconductor lattice parameters to be less critical to magnetic moments than magnetic anisotropy

XPS and XMCD study of Fe3O4/GaAs interface

Ultrathin Fe oxide films of various thicknesses prepared by post-growth oxidation on GaAs(100) surface have been investigated with X-ray photoelectron spectroscopy (NPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). The XPS confirms that the surfaces of the oxide are Fe3O4 rather than Fe2O3. XAS and XMCD measurements indicate the presence of nsulating Fe divalent oxide phases (FeO) beneath the surface Fe-3 O-4 layer with the sample thickness above 4 mn. This FeO might act as a barrier for the spin injection into the GaAs