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  • 1.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Michalak, L.
    Kalmar University.
    Canali, C. M.
    Kalmar University.
    Samuelson, L.
    Lund University.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Tunneling anisotropic magnetoresistance in Co/AlOx/Au tunnel junctions2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 3, p. 848-852Article in journal (Refereed)
    Abstract [en]

    We observe spin-valve-like effects in nanoscaled thermally evaporated Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and depends on the relative orientation of the magnetization direction of the Co electrode with respect to the current direction. We attribute this effect to a two-step magnetization reversal and an anisotropic density of states resulting from spin-orbit interaction. The results of this study points to future applications of novel spintronics devices involving only one ferromagnetic layer.

  • 2.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Lund University, Lund, Sweden.
    Michalak, Lukasz
    Linnaeus University, Kalmar, Sweden.
    Canali, Carlo
    Linnaeus University, Kalmar, Sweden.
    Samuelson, Lars
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Tunneling Anisotropic Magnetoresistance in Co/AlOx /Au Tunnel Junctions2008Conference paper (Refereed)
    Abstract [en]

    We observe spin-valve-like effects in nano-scaled thermally evaporated Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and depends on the relative orientation of the magnetization direction of the Co electrode with respect to the current direction. We attribute this effect to a two-step magnetization reversal and an anisotropic density of states resulting from spin-orbit interaction. The results of this study points to future applications of novel spintronics devices involving only one ferromagnetic layer.

  • 3.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Michalak, L.
    Kalmar University.
    Canali, C. M.
    Kalmar University.
    Suyatin, D.
    Lund University.
    Samuelson, L.
    Lund University.
    Large magnetoresistance in Co/Ni/Co ferromagnetic single electron transistors2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 12, p. 123111-Article in journal (Refereed)
    Abstract [en]

    The authors report on magnetotransport investigations of nanoscaled ferromagnetic Co/Ni/Co single electron transistors. As a result of reduced size, the devices exhibit single electron transistor characteristics at 4.2 K. Magnetotransport measurements carried out at 1.8 K reveal tunneling magnetoresistance (TMR) traces with negative coercive fields, which the authors interpret in terms of a switching mechanism driven by the shape anisotropy of the central wirelike Ni island. A large TMR of about 18% is observed within a finite source-drain bias regime. The TMR decreases rapidly with increasing bias, which the authors tentatively attribute to excitation of magnons in the central island.

  • 4.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS).
    Michalak, L.
    Department of Chemistry and Biomedical Sciences, Kalmar University.
    Canali, C.M.
    Department of Chemistry and Biomedical Sciences, Kalmar University.
    Samuelson, L.
    Solid State Physics/ the Nanometer Structure Consortium, Lund University.
    Probing spin accumulation in Ni/Au/Ni single-electron transistors with efficient spin injection and detection electrodes2007In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, no 1, p. 81-85Article in journal (Refereed)
    Abstract [en]

    We have investigated spin accumulation in Ni/Au/Ni single-electron transistors assembled by atomic force microscopy. The fabrication technique is unique in that unconventional hybrid devices can be realized with unprecedented control, including real-time tunable tunnel resistances. A grid of Au disks, 30 nm in diameter and 30 nm thick, is prepared on a SiO2 surface by conventional e-beam writing. Subsequently, 30 nm thick ferromagnetic Ni source, drain, and side-gate electrodes are formed in similar process steps. The width and length of the source and drain electrodes were different to exhibit different coercive switching fields. Tunnel barriers of NiO are realized by sequential Ar and O2 plasma treatment. By use of an atomic force microscope with specially designed software, a single nonmagnetic Au nanodisk is positioned into the 25 nm gap between the source and drain electrodes. The resistance of the device is monitored in real time while the Au disk is manipulated step-by-step with angstrom-level precision. Transport measurements in magnetic field at 1.7 K reveal no clear spin accumulation in the device, which can be attributed to fast spin relaxation in the Au disk. From numerical simulations using the rate-equation approach of orthodox Coulomb blockade theory, we can put an upper bound of a few nanoseconds on the spin-relaxation time for electrons in the Au disk. To confirm the magnetic switching characteristics and spin injection efficiency of the Ni electrodes, we fabricated a test structure consisting of a Ni/NiO/Ni magnetic tunnel junction with asymmetric dimensions of the electrodes similar to those of the single-electron transistors. Magnetoresistance measurements on the test device exhibited clear signs of magnetic reversal and a maximum tunneling magnetoresistance of 10%, from which we deduced a spin polarization of about 22% in the Ni electrodes. © 2007 American Chemical Society.

  • 5.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Pettersson, Håkan
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Michalak, Lukasz
    Högskolan i Kalmar, Kalmar, Sweden.
    Canali, C. M.
    Linné Universitetet, Kalmar, Sweden.
    Samuelson, Lars
    Avd. f. Fasta Tillståndets Fysik, Lunds Universitet.
    Ferromagnetic single-electron transistors fabricated by atomic force microscopy2006Conference paper (Refereed)
    Abstract [en]

    We report on the fabrication and magneto-transport measurements of Ni/Au/Ni ferromagnetic single-electron transistors (F-SETs), fabricated by atomic force microscopy. By positioning a single Au disc (30 nm in diameter) into the gap between the Ni drain and source electrodes (of width 220 nm and 80 nm, respectively) step-by-step with Angstrom precision, and using plasma-processed NiOx as tunneling barriers, we can successfully fabricate F-SETs of high quality and substantial stability. The characteristic time interval of the device between two successive tunneling events is 10ps. The absence of any clear features in the transport related to the applied external magnetic field indicates that no spin-accumulation is maintained in the central Au disc. This interesting result indicates that the spin-relaxation time inside the central island should be shorter than 10ps. Based on these findings, we will discuss possible mechanisms of spin-relaxation in metal nano-structures triggered by spin-orbit interaction.

  • 6.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Suyatin, D.
    Solid State Physics/ the Nanometer Structure Consortium, Lund University, Sweden.
    Michalak, L.
    Dept of Chemistry and Biomedical Sciences, Kalmar University, Sweden.
    Canali, C. M.
    Dept of Chemistry and Biomedical Sciences, Kalmar University, Sweden.
    Samuelson, L.
    Solid State Physics/ the Nanometer Structure Consortium, Lund University, Sweden.
    Nanoscaled Ferromagnetic Single-Electron Transistors2007In: 2007 7th IEEE International Conference on Nanotechnology - IEEE-NANO 2007, Proceedings, Piscataway, N.J.: IEEE Press, 2007, p. 420-421Conference paper (Other academic)
    Abstract [en]

    We report on a summary of fabricating and characterizing nanoscaled ferromagnetic single-electron transistors (F-SETs). One type of device is assembled with an atomic force microscope. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with Angstrom precision into the gap between plasma oxidized Ni source and drain electrodes which are designed with different geometries to facilitate magnetic moment reversal at different magnetic fields. The tunnel resistances can be tuned in real-time during the device fabrication by re-positioning the An disc. A second type of device with Co electrodes and a central Au island is fabricated using a high-precision alignment procedure invoked during e-beam writing. Both devices exhibit single-electron transistor characteristics at 4.2K. From magnetotransport measurements carried out at 1.7K, we found that it is more efficient to realize spin injection and detection in Co/Au/Co devices fabricated with the second technique. A maximum TMR of about 4% was observed in these devices.

  • 7.
    Liu, Ruisheng S.
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Canali, C. M.
    Kalmar University, Kalmar, Sweden.
    Samuelson, L.
    Lund University, Lund, Sweden.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Magnetoresistance studies on CoAl OX Au and CoAl OX NiAu tunnel structures2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 20, p. 203107-203107-3Article in journal (Refereed)
    Abstract [en]

    We report on magnetoresistance (MR) studies on CoAl OX Au and CoAl OX NiAu magnetic tunnel junctions. In spite of the fact that the difference between the two samples is merely a 3 nm thick Ni layer, there is a sharp contrast in MR behavior indicating that the electronic structure at the interface between the ferromagnetic electrodes and the insulating barrier dominates the MR signal. The former sample exhibits a clear tunneling anisotropic MR (TAMR), with the characteristic correlation between resistance and current direction, in contrast to the latter sample which displays a conventional tunneling MR (TMR) dominated by the relative orientation between the magnetization directions of the two electrodes. In addition, the TAMR has a much stronger temperature dependence than the TMR, indicating a much faster drop-off of the tunneling density of states anisotropy than the tunneling electron spin polarization with increasing temperature. Finally, we propose a possible simple way to distinguish TAMR from normal TMR by measuring the resistance of the device at different angles of the external magnetic field. 2008 American Institute of Physics.

  • 8.
    Liu, Ruisheng
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Suyatin, D.
    Lund University.
    Pettersson, Håkan
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), Applied Mathematics and Physics (CAMP).
    Samuelson, L.
    Lund University.
    Assembling ferromagnetic single-electron transistors by atomic force microscopy2007In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 18, no 5, p. 055302-Article in journal (Refereed)
    Abstract [en]

    We demonstrate the assembly of nanoscale ferromagnetic single-electron transistors using atomic force microscopy for imaging as well as for nanoscale manipulation. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with angstrom precision into the gap between a plasma-oxidized Ni source and drain electrodes. The tunnel resistances can be tuned in real time during the device fabrication by repositioning the Au disc. Transport measurements reveal long-term stable single-electron transistor characteristics at 4.2 K. The well-controlled devices with very small central islands facilitate future in-depth studies of the interplay between Coulomb blockade, spin-dependent tunnelling and spin accumulation in ferromagnetic single-electron transistors at elevated temperatures.

  • 9.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Liu, Ruisheng S.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab.
    Suyatin, Dmitry
    Avdelningen för Fasta Tillståndets Fysik (FTF), Lunds Universitet.
    Samuelson, Lars
    Avdelningen för Fasta Tillståndets Fysik (FTF), Lunds Universitet.
    Assembling ferromagnetic single-electron transistors by atomic force microscopy2008In: Nanostructures in electronics and photonics / [ed] Rahman, Faiz, Singapore: Pan Stanford Publishing, 2008, p. 29-40Chapter in book (Refereed)
  • 10.
    Pettersson, Håkan
    et al.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS). Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Liu, Ruisheng S.
    Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Suyatin, Dmitry
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Samuelson, Lars
    Solid State Physics and the Nanometer Structure Consortium, Lund University, Lund, Sweden.
    Assembling ferromagnetic single-electron transistors with atomic force microscopy2008In: Nanostructures in Electronics and Photonics / [ed] Faiz Rahman, London: Pan Stanford Publishing, 2008, p. 29-40Chapter in book (Other academic)
    Abstract [en]

    Ferromagnetic Single Electron Transistors (F-SETs) comprise ferromagnetic electrodes connected to a ferromagnetic- or non-magnetic central island via tunnel barriers. These devices are important for studies of spin-transport physics in confined structures. Here we describe the development of a novel type of AFMassembled nano-scale F-SETs suitable for spin-transport investigations at temperatures above 4.2 K. The ingenious fabrication technique means that their electrical characteristics can be tuned in real-time during the fabrication sequence by re-positioning the central island with Ångström precision. © 2008 by Pan Stanford Publishing Pte. Ltd. All rights reserved.

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