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13 Jun 2011

Volume 98, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 243101 (2011); http://dx.doi.org/10.1063/1.3598468 (3 pages)

M. Beleggia, T. Kasama, R. E. Dunin-Borkowski, S. Hofmann, and G. Pozzi
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Spin current generation due to mechanical rotation in the presence of impurity scattering

Mamoru Matsuo, Jun’ichi Ieda, Eiji Saitoh, and Sadamichi Maekawa

Appl. Phys. Lett. 98, 242501 (2011); http://dx.doi.org/10.1063/1.3597220 (3 pages)

Online Publication Date: 13 June 2011

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We investigate theoretically the generation of a spin current from a uniformly rotating body with impurity scattering based on the spin-dependent transport equation. If the cyclotron frequency is lower than the inverse of the relaxation time, the spin current is then created mainly in the radial direction when a weak magnetic field is applied parallel to the rotation axis. Spin accumulation is estimated by solving the spin diffusion equation. We show that the inverse spin Hall effect can be used to detect the spin current induced by rotation.
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72.25.-b Spin polarized transport
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.My Galvanomagnetic and other magnetotransport effects

Thickness-dependent magnetism and spin-glass behaviors in compressively strained BiFeO3 thin films

Ching-Jung Cheng, Chengliang Lu, Zuhuang Chen, Lu You, Lang Chen, Junling Wang, and Tom Wu

Appl. Phys. Lett. 98, 242502 (2011); http://dx.doi.org/10.1063/1.3600064 (3 pages) | Cited 6 times

Online Publication Date: 13 June 2011

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Compressively strained BiFeO3 (BFO) films from 19 to 114 nm are epitaxially grown on LaAlO3 substrates, and their thickness-dependent evolutions of structural and magnetic properties are investigated. Across the morphotropic phase boundary, complex strain relaxation behaviors involving low-symmetry intermediate/bridging phases are observed. The fully strained 38 nm BFO film exhibits a saturation magnetization of ∼ 28 emu/cm3 at 300 K with a coercivity of 130 Oe while all films show a spin-glass behavior. These findings suggest that tailoring film thickness is effective to suppress the cycloidal magnetic modulation in BFO, leading to magnetic properties different from the bulk counterpart.
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75.70.Ak Magnetic properties of monolayers and thin films
75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
68.60.Bs Mechanical and acoustical properties
75.50.Lk Spin glasses and other random magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

L10 FePt based exchange coupled composite bit patterned films

A. T. McCallum, P. Krone, F. Springer, C. Brombacher, M. Albrecht, E. Dobisz, M. Grobis, D. Weller, and O. Hellwig

Appl. Phys. Lett. 98, 242503 (2011); http://dx.doi.org/10.1063/1.3599573 (3 pages) | Cited 11 times

Online Publication Date: 14 June 2011

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We demonstrate a 2.5-fold coercivity reduction in FePt based exchange coupled composite bit patterned media (ECC-BPM) by coupling a lower anisotropy Co/Pd–Co/Ni-multilayer system to the top of a high anisotropy FePt L10 film. Furthermore the tight switching field distribution (SFD) of the lower anisotropy system reduces the SFD of the ECC-BPM composite system compared to a single layer FePt film. The relative amount of switching field and SFD reduction in these ECC-BPM arrays agree with corresponding micromagnetic simulations.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

Little–Parks oscillations at low temperatures: Gigahertz resonator method

Andrey Belkin, Matthew Brenner, Thomas Aref, Jaseung Ku, and Alexey Bezryadin

Appl. Phys. Lett. 98, 242504 (2011); http://dx.doi.org/10.1063/1.3593482 (3 pages) | Cited 1 time

Online Publication Date: 14 June 2011

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A thin-film Fabry–Perot superconducting resonator is used to reveal the Little and Parks (LP) effect [ Phys. Rev. Lett. 9, 9 (1962)] , even at temperatures much lower than the critical temperature. A pair of parallel nanowires is incorporated into the resonator at the point of the supercurrent antinode. As the magnetic field is ramped, Meissner currents develop, changing the resonance frequency of the resonator. The LP oscillation is revealed as a periodic set of distorted parabolas observed in the transmission of the resonator and corresponds to the states of the wire loop having different vorticities. We also report a direct observation of single and double phase slip events.
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85.25.-j Superconducting devices

Manipulation of magnetization states of ferromagnetic nanorings by an applied azimuthal Oersted field

T Yang, Nihar R. Pradhan, Abby Goldman, Abigail S. Licht, Yihan Li, M. Kemei, Mark T. Tuominen, and Katherine E. Aidala

Appl. Phys. Lett. 98, 242505 (2011); http://dx.doi.org/10.1063/1.3599714 (3 pages) | Cited 4 times

Online Publication Date: 16 June 2011

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We manipulate the magnetic states of ferromagnetic nanorings with an azimuthal Oersted field directed along the ring circumference. The circular field is generated by passing current through an atomic force microscope tip positioned at the center of the ring, and can directly control the chirality of the vortex state. We demonstrate switching from an onion state to a vortex state and between two vortex states, using magnetic force microscopy to image the resulting magnetic states. The understanding of the magnetization switching behavior in an azimuthal Oersted field could improve practical magnetic data storage devices.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures

Multiple-mode excitation in spin-transfer nanocontacts with dynamic polarizer

N. Wang, X. L. Wang, W. Qin, S. H. Yeung, D. T. K. Kwok, H. F. Wong, Q. Xue, P. K. Chu, C. W. Leung, and A. Ruotolo

Appl. Phys. Lett. 98, 242506 (2011); http://dx.doi.org/10.1063/1.3600328 (3 pages)

Online Publication Date: 16 June 2011

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We report our study on the emission response of a magnetic nanocontact with dynamic polarizer in perpendicular magnetic field. In this configuration three modes are accessible, two of which correspond to the precessional motion of a vortex in one of the two ferromagnetic layers with the other working as a static polarizer. At high currents a third mode can be observed that is ascribed to the simultaneous precession of two vortices, one in each layer, with the other layer working as a dynamic polarizer.
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85.70.Ay Magnetic device characterization, design, and modeling
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
81.07.Lk Nanocontacts

Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface

Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani, and Koichiro Inomata

Appl. Phys. Lett. 98, 242507 (2011); http://dx.doi.org/10.1063/1.3600645 (3 pages) | Cited 7 times

Online Publication Date: 16 June 2011

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The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density (KU) of 2–3×106 erg/cm3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions (MTJs) with high thermal stability at sub-50-nm dimension. The CFA thickness dependence of KU was investigated at different annealing temperatures, indicating that the perpendicular anisotropy of CFA is contributed by the interfacial anisotropy between CFA and MgO. This letter will open up a way for obtaining perpendicular magnetization of Co-based full-Heusler alloys, which is promising for further reduction in the critical current of current induced magnetization switching in MgO-based MTJ nanopillars with perpendicular full-Heusler alloy electrodes.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
75.75.-c Magnetic properties of nanostructures
75.78.Jp Ultrafast magnetization dynamics and switching
68.60.Dv Thermal stability; thermal effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

The effect of film and interface structure on the transport properties of Heusler based current-perpendicular-to-plane spin valves

V. K. Lazarov, K. Yoshida, J. Sato, P. J. Hasnip, M. Oogane, A. Hirohata, and Y. Ando

Appl. Phys. Lett. 98, 242508 (2011); http://dx.doi.org/10.1063/1.3600792 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2011

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We present direct link between the transport properties of Co2MnSi and Co2FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2FeMnSi electrodes is L21 but their interface with the CoSi spacer is disordered. In contrast to the Co2FeMnSi-electrodes, the Co2MnSi-electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L21. The magnetoresistance of the Co2MnSi-SV is over two orders of magnitude better than those of Co2FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.47.Np Metals and alloys

The effect of the static magnetic susceptibility on the spin precession in MgO based magnetic tunnel junction

Ung-Hwan Pi, Sung-Chul Lee, Kwang-Seok Kim, Keewon Kim, Jay-Kwang Shin, and U-in Chung

Appl. Phys. Lett. 98, 242509 (2011); http://dx.doi.org/10.1063/1.3601463 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2011

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We studied the steady state precession of the spins in the magnetic tunnel junctions. In the field range below the spin-flop transition of synthetic antiferromagnetic pinned layer, the precession mode depends upon the current bias polarity. Above the spin-flop transition, however, the spin precession shows symmetric behavior on the current bias. The dominant mechanism of the spin precession changes from the spin transfer torque to thermal excitation at around the spin-flop transition. The enhancement of thermal fluctuation above the spin-flop transition is analyzed in relation to the static magnetic susceptibility.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Ds Spin waves

Biaxially textured cobalt-doped BaFe2As2 films with high critical current density over 1 MA/cm2 on MgO-buffered metal-tape flexible substrates

Takayoshi Katase, Hidenori Hiramatsu, Vladimir Matias, Chris Sheehan, Yoshihiro Ishimaru, Toshio Kamiya, Keiichi Tanabe, and Hideo Hosono

Appl. Phys. Lett. 98, 242510 (2011); http://dx.doi.org/10.1063/1.3599844 (3 pages) | Cited 16 times

Online Publication Date: 17 June 2011

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High critical current densities (Jc)>1 MA/cm2 were realized in cobalt-doped BaFe2As2 (BaFe2As2:Co) films on flexible metal substrates with biaxially textured MgO base-layers fabricated by an ion-beam assisted deposition technique. The BaFe2As2:Co films showed small in-plane crystalline misorientations (ΔϕBaFe2As2:Co) of ∼ 3° regardless of twice larger misorientations of the MgO base-layers (ΔϕMgO = 7.3°), and exhibited high self-field Jc up to 3.5 MA/cm2 at 2 K. These values are comparable to that on MgO single crystals and the highest Jc among iron pnictide superconducting tapes and wires ever reported. High in-field Jc suggests the existence of c-axis correlated vortex pinning centers.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Improved coherence of ultrafast spin-transfer-driven precessional switching with synthetic antiferromagnet perpendicular polarizer

A. Vaysset, C. Papusoi, L. D. Buda-Prejbeanu, S. Bandiera, M. Marins de Castro, Y. Dahmane, J.-C. Toussaint, U. Ebels, S. Auffret, R. Sousa, L. Vila, and B. Dieny

Appl. Phys. Lett. 98, 242511 (2011); http://dx.doi.org/10.1063/1.3597797 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2011

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The coherence of the precessional switching was compared in planar spin-valves comprising either an additional simple perpendicular polarizer or a synthetic antiferromagnet perpendicular polarizer. A significant improvement in the precession coherence was observed experimentally in the second type of samples. Micromagnetic simulations were performed to study the effect of the stray field from the perpendicular polarizer. They provide an explanation for the gradual loss of coherence of the precession in terms of vortex formation, which occurs much faster when a simple perpendicular polarizer is used.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Ci Filters, zone plates, and polarizers
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