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30 Jul 2007

Volume 91, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 91, 052901 (2007); http://dx.doi.org/10.1063/1.2767146 (3 pages)

Wei-Feng Rao and Yu U. Wang
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35% magnetocurrent with spin transport through Si

Biqin Huang, Lai Zhao, Douwe J. Monsma, and Ian Appelbaum

Appl. Phys. Lett. 91, 052501 (2007); http://dx.doi.org/10.1063/1.2767198 (3 pages) | Cited 14 times

Online Publication Date: 30 July 2007

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Efficient injection of spin-polarized electrons into the conduction band of silicon is limited by the formation of a silicide at the ferromagnetic metal (FM)/silicon interface. In the present work, this “magnetically dead” silicide (where strong spin scattering significantly reduces injected spin polarization) is eliminated by moving the FM in the spin injector from the tunnel junction base anode to the emitter cathode and away from the silicon surface. This results in over an order-of-magnitude increase in spin injection efficiency, from a previously reported magnetocurrent ratio of ≈ 2% to ≈ 35% and an estimated spin polarization in Si from ≈ 1% to at least ≈ 15%. The injector tunnel junction bias dependence of this spin transport signal is also measured, demonstrating the importance of low bias voltage to preserve high injected spin polarization.
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72.25.Dc Spin polarized transport in semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Cw Elemental semiconductors

Structural and magnetic properties of spin- and charge-doped Sr0.8La0.2Ti0.9Co0.1O3

J. Yang, Y. P. Lee, and B. W. Lee

Appl. Phys. Lett. 91, 052502 (2007); http://dx.doi.org/10.1063/1.2767203 (3 pages) | Cited 3 times

Online Publication Date: 30 July 2007

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The structural and the magnetic properties of spin- and charge-doped Sr0.8La0.2Ti0.9Co0.1O3 have been investigated. The sample shows a cubic structure at room temperature. The temperature dependence of magnetization (M) of Sr0.8La0.2Ti0.9Co0.1O3, in both zero-field-cooled (ZFC) and field-cooled (FC) modes between 100 and 70 000 Oe, was measured. It is found that the sample undergoes the paramagnetic-ferrimagnetic phase transition at around 50 K, and the MZFC curve lies above the MFC one below 32 K when the applied field is less than 2000 Oe. This unusual behavior can be understood as a superposition of ferrimagnetic and paramagnetic contributions to the magnetization.
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61.66.Fn Inorganic compounds
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.Ck Nonmetals
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Switching of tunnel magnetoresistance by domain wall motion in (Ga,Mn)As-based magnetic tunnel junctions

M. Fukuda, M. Yamanouchi, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 91, 052503 (2007); http://dx.doi.org/10.1063/1.2767230 (3 pages) | Cited 2 times

Online Publication Date: 30 July 2007

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Switching of tunnel magnetoresistance in magnetic tunnel junctions (MTJs) has been achieved by magnetic domain wall motion in one of the electrodes. The fabricated devices have two (Ga,Mn)As-based MTJs with a common bottom (Ga,Mn)As electrode, in which the domain wall motion takes place both by magnetic field and by current. This configuration allows not only the observation of switching but also time-resolved detection of the position of the domain wall by the tunnel magnetoresistance.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
82.45.Vp Semiconductor materials in electrochemistry

Structural and magnetic properties of (In1−xFex)2O3 (0.0 ⩽ x ⩽ 0.25) system: Prepared by gel combustion method

O. D. Jayakumar, I. K. Gopalakrishnan, S. K. Kulshreshtha, Amita Gupta, K. V. Rao, D. V. Louzguine-Luzgin, A. Inoue, P.-A. Glans, J.-H. Guo, K. Samanta, M. K. Singh, and R. S. Katiyar

Appl. Phys. Lett. 91, 052504 (2007); http://dx.doi.org/10.1063/1.2757589 (3 pages) | Cited 25 times

Online Publication Date: 30 July 2007

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(In1−xFex)2O3 polycrystalline samples with x = (0.0,0.05,0.10,0.15,0.20, and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of x-ray diffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy imaging, indexing of the selected-area electron diffraction patterns, x-ray absorption spectroscopy, and Raman Spectroscopy. dc magnetization studies as a function of temperature and field indicate that they are ferromagnetic with Curie temperature (TC) well above room temperature.
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81.05.Cy Elemental semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.70.Dm X-ray absorption spectra
78.30.Hv Other nonmetallic inorganics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Thermoelectric property studies on bulk TiOx with x from 1 to 2

Qinyu He, Qing Hao, Gang Chen, Bed Poudel, Xiaowei Wang, Dezhi Wang, and Zhifeng Ren

Appl. Phys. Lett. 91, 052505 (2007); http://dx.doi.org/10.1063/1.2767775 (3 pages) | Cited 12 times

Online Publication Date: 1 August 2007

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100% dense bulk TiOx samples have been made by first oxidizing TiO and then direct current induced hot press. It was found that the Seebeck coefficients are negative at room temperature and change to positive at higher temperature for 1<x<1.25, positive at room temperature and change to negative at higher temperature for 1.25<x<5/3, and always negative up to 800 °C for 5/3<x<2. The highest achieved dimensionless figure of merit is about 0.2–0.23 for 1.83<x<1.9, about eight times lower than the reported value.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Sk Insulators
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Probing the random distribution of half-metallic Co2Mn1−xFexSi Heusler alloys

Sabine Wurmehl, Jürgen T. Kohlhepp, Henk J. M. Swagten, Bert Koopmans, Marek Wójcik, Benjamin Balke, Christian G. F. Blum, Vadim Ksenofontov, Gerhard H. Fecher, and Claudia Felser

Appl. Phys. Lett. 91, 052506 (2007); http://dx.doi.org/10.1063/1.2760158 (3 pages) | Cited 14 times

Online Publication Date: 1 August 2007

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Co2Mn1−xFexSi Heusler alloys crystallize in the L21 structure. This structure type requires random distribution of Mn and Fe in case of the mixed alloys. The spin echo nuclear magnetic resonance (NMR) technique probes the direct local environments of the active atoms and is thus able to resolve next neighboring shells providing a unique tool to verify the random distribution of Mn and Fe in Co2Mn1−xFexSi. Exemplarily, the half-metallic quaternary Heusler alloy Co2Mn0.5Fe0.5Si was investigated by means of NMR. The 55Mn NMR measurements unambiguously demonstrate the random distribution of Mn and Fe on the 4b Wyckoff position in Co2Mn0.5Fe0.5Si.
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61.66.Dk Alloys
76.60.Lz Spin echoes

Spin transfer switching in current-perpendicular-to-plane spin valve observed by magneto-optical Kerr effect using visible light

Ken-ichi Aoshima, Nobuhiko Funabashi, Kenji Machida, Yasuyoshi Miyamoto, Norikazu Kawamura, Kiyoshi Kuga, Naoki Shimidzu, Fumio Sato, Takashi Kimura, and Yoshichika Otani

Appl. Phys. Lett. 91, 052507 (2007); http://dx.doi.org/10.1063/1.2767770 (3 pages) | Cited 11 times

Online Publication Date: 2 August 2007

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The authors have succeeded in optically observing the spin transfer switching (STS) in a current-perpendicular-to-plane spin-valve device. The device consists of three spin-valve elements, each of which comprises of a transparent top electrode, free and pinned magnetic layers separated by a copper spacer, and a bottom copper electrode. Despite a relatively large device resistance, spin transfer switching of the free layer was carried out using the spin injection from the transparent top electrode. Magneto-optical Kerr effect measurements performed through the transparent top electrode show clear changes in the signal synchronized with the resistance change as a result of the STS.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
78.20.Ls Magneto-optical effects

Top-down and bottom-up through-thickness current anisotropy in a bilayer YBa2Cu3O7−x film

Z. J. Chen, D. M. Feldmann, D. C. Larbalestier, T. G. Holesinger, X. Li, W. Zhang, and M. W. Rupich

Appl. Phys. Lett. 91, 052508 (2007); http://dx.doi.org/10.1063/1.2767772 (3 pages) | Cited 11 times

Online Publication Date: 2 August 2007

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The authors find the critical current anisotropy of a bilayer YBa2Cu3O7−δ film with different pinning structures in each layer is the sum of the anisotropy of the two individual layers, revealing that it is possible to tune the anisotropy of the composite through variation of an individual layer’s thickness and pinning structure. YBa2Cu4Ox intergrowths and Dy2O3 nanodots were the dominant pinning structures in the top and bottom layers, respectively. The bottom layer of the composite was isolated using traditional Ar+ ion milling and the top layer was isolated using a focused ion beam, allowing each layer to be studied independently.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.Na Mesoscopic and nanoscale systems

Different acceptor behaviors in two-dimensional hole gas system formed in Mn-doped GaAs/p-AlGaAs ferromagnetic heterostructures

Jiqing Wang, Bin Lv, Huibing Mao, Qiang Zhao, Jianguo Yu, Yan Liu, Yong Zhang, Ziqiang Zhu, and Huaizhong Xing

Appl. Phys. Lett. 91, 052509 (2007); http://dx.doi.org/10.1063/1.2768001 (3 pages) | Cited 1 time

Online Publication Date: 2 August 2007

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The authors investigated the ferromagnetic property of dual acceptors (Be and Mn) doped GaAs/AlGaAs heterostructures by means of numerical self-consistent field calculation. The dependence of the magnetic behavior on both acceptor doping concentrations and modes was studied in the two-dimensional hole gas system. The results show different dependences of Curie temperature on the concentration of each acceptor, which is attributed to different doping conditions and mechanisms. In addition, the ferromagnetic transition temperature can be increased by about 70 K as a result of introducing Be δ-doping layer in AlGaAs barrier, as compared with that for Be bulk doping. The theoretical results indicate that double acceptor δ-doped ferromagnetic heterostructures have potential advantage in the realm of spintronic application.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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