Spin dependent electron transport across ferromagnet/ GaAs Schottky barrier interfaces has been investigated at room temperature using photoexcitation techniques. We carried out a careful quantitative analysis that enabled us to precisely separate magneto-optical effects and spin filtering. Significant spin filtering effects were seen in NiFe/ GaAs and Fe/ GaAs structures at forward bias, whereas at reverse bias only magnetic circular dichroism was found. The observed effect strongly depends on the details of the Schottky barrier, suggesting that electron tunneling is the relevant transport mechanism.
We have investigated a new magnetic labelling technology for high-throughput biomolecular identification and DNA sequencing. Planar multi-bit magnetic tags comprising a magnetic barcode formed by an ensemble of micron-sized thin film ferromagnetic Co bars and a 15 x 15 micron Au square for immobilization of probe molecules have been designed and fabricated. We show that by using a globally applied magnetic field and magneto-optical Kerr microscopy the magnetic elements in the multi-bit magnetic tags can be addressed individually and encoded/decoded remotely. The power of the approach is the read/write technique, which allows modest globally applied magnetic fields to write almost unlimited numbers of codes to populations of tags rather than individuals. The magnetic nature of the technology also lends itself naturally to fast, remote decoding and the ability to rewrite tags if needed. We demonstrate the critical steps needed to show the feasibility of this technology, including fabrication, remote writing and reading, and successful functionalization of the tags as verified by fluorescence detection. This approach is ideal for encoding information on tags in microfluidic flow or suspension, in order to label oligonucleotides during split-and-mix synthesis, and for combinatorial library-based high-throughput multiplexed bioassays.
We have investigated both static and dynamic magnetic properties of square antidot arrays in a ferromagnetic thin-film structure of Au ͑2 nm͒/Ni 80 Fe 20 ͑27.6 nm͒ on a SiO 2 500 nm/Si substrate using magneto-optic Kerr effect magnetometry, Brillouin light scattering ͑BLS͒, and micromagnetic simulations. The antidot patterns were 1 m square holes arranged in two separate square lattices of dot separations d = 0.6 m and 1.0 m. The introduction of antidots induced an in-plane fourfold magnetic anisotropy with hard axes on the two nearest-antidot-neighbor directions. The coercive field, H c , was increased by the presence of antidots. Fixed-frequency modes were observed in spin-wave dispersion relations in remanent spin configurations. These modes correspond to spin-wave confinement by antidot edges, which were seen as a series of nodal lines parallel to the edges in simulated spin-wave mode spatial mappings. Domains in remanent states, some of which were responsible for the existence of dipole-exchange backward volume modes seen in BLS spectra, were also found to confine spin waves in simulations.
We present a study of the influence of substrate roughness on the magnetic properties of thin fcc Co films ͑7 and 17 nm thick͒ grown on Cu͑001͒/Si͑001͒. A significant decrease in cubic anisotropy with increasing film roughness was observed with Brillouin light scattering and magneto-optical Kerr effect magnetometry. In addition, the rougher samples showed a substantial broadening of the spin wave peaks. Both effects were found to be more pronounced for the thinner Co layers. Our observations are discussed in the framework of a theoretical model which takes into account the morphology of the Co films as measured by atomic force microscopy. While roughness effects are usually discussed in the context of Néel's "orange-peel" model, we propose a qualitatively different effect in this work whereby the magnetization follows coherently the substrate morphology ͑"undulating" state͒ resulting in the absence of magnetic surface charges. This magnetic configuration gives rise to a reduction in the magnetic anisotropy of epitaxial thin films, which is in good qualitative agreement with the experimental observations.
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