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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Spin-current pulse induced switching of vortex chirality in permalloy/Cu/Co nanopillars

B. C. Choi, J. Rudge, E. Girgis, J. Kolthammer, Y. K. Hong, and A. Lyle

Appl. Phys. Lett. 91, 022501 (2007); http://dx.doi.org/10.1063/1.2756109 (3 pages) | Cited 15 times

Online Publication Date: 9 July 2007

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Dynamic response of the vortex magnetization in multilayered magnetic nanopillars to the spin-polarized current pulse has been investigated numerically. The equilibrium magnetization configurations in both magnetic layers are the vortex states with single magnetization cores at the disk center. It was found that the chirality of the vortex state in magnetic free layer can be controllably switched by applying current pulse with appropriate amplitude, polarity, and duration. The critical current density required for the chirality switching is found to be on the order of 108 A/cm2.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.63.Bd Nanocrystalline materials
72.25.Mk Spin transport through interfaces
75.40.Mg Numerical simulation studies

Origin of recoil hysteresis loops in Sm–Co/Fe exchange-spring magnets

Y. Choi, J. S. Jiang, J. E. Pearson, S. D. Bader, and J. P. Liu

Appl. Phys. Lett. 91, 022502 (2007); http://dx.doi.org/10.1063/1.2752534 (3 pages) | Cited 12 times

Online Publication Date: 10 July 2007

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Open recoil loops are often interpreted as a consequence of a breakdown in exchange coupling and attributed to the decoupled soft phase in exchange-coupled permanent magnets. However, in element-specific recoil loop measurements on Sm–Co/Fe exchange spring magnets, the authors found that the open recoil loops were present not only in the soft (Fe) layer but also in the hard (Sm–Co) layer, and were not a consequence of exchange coupling breakdown between the soft and hard layers. Comparison between the experimental results and micromagnetic calculations reveals that the observed open recoil loops originate from the anisotropy variations in the Sm–Co layer.
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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.Et Exchange and superexchange interactions
75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy

Ferromagnetic Mn moments at SrRuO3/SrMnO3 interfaces

Y. Choi, Y. Z. Yoo, O. Chmaissem, A. Ullah, S. Kolesnik, C. W. Kimball, D. Haskel, J. S. Jiang, and S. D. Bader

Appl. Phys. Lett. 91, 022503 (2007); http://dx.doi.org/10.1063/1.2753100 (3 pages) | Cited 5 times

Online Publication Date: 10 July 2007

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Using element-specific, x-ray probes of magnetism the authors observe a net ferromagnetic moment from Mn in SrRuO3/SrMnO3 (SRO/SMO) superlattice films. It is found that the magnetic behavior of the SRO and SMO layers is significantly modified by their exchange interaction. Bulk magnetometry shows a two-step, easy-axis magnetization reversal process and x-ray measurements confirm that the reversal with higher coercivity involves the magnetization in the SMO layers. The results provide strong evidence for the presence of pinned SRO magnetization at the SRO/SMO interface. Angle-dependent measurements reveal that the net Mn moment is due to a canted antiferromagnetic spin configuration in the SMO layers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions

Spin accumulation in lateral all-ferromagnetic spin valves

B. C. Lee, Tae-Suk Kim, Kungwon Rhie, and Jinki Hong

Appl. Phys. Lett. 91, 022504 (2007); http://dx.doi.org/10.1063/1.2753704 (3 pages) | Cited 1 time

Online Publication Date: 10 July 2007

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Spin accumulation in magnetic tunnel junctions and lateral all-ferromagnetic spin valves is theoretically investigated by using a spin-dependent diffusive transport model. When electric current tunnels through a barrier, spin accumulation occurs in the ferromagnetic layer and can be detected with nonlocal spin valve measurements. Depending on the relative orientation of magnetization, the nonlocal spin signal has three different values and can determine the bulk spin polarization of the ferromagnetic material.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.40.Gk Tunneling
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Tuning exchange-bias properties by thermal effects in a hard/soft bilayer

T. Hauet, S. Mangin, F. Montaigne, J. A. Borchers, and Y. Henry

Appl. Phys. Lett. 91, 022505 (2007); http://dx.doi.org/10.1063/1.2753108 (3 pages) | Cited 2 times

Online Publication Date: 12 July 2007

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The effect of temperature on exchange-bias properties of an antiferromagnetically coupled hard/soft bilayer (Tb12Fe88/Gd40Fe60) is studied. In a similar manner to its cooling field dependence, a continuous transition from a negative to a positive exchange-bias field is observed with increasing temperature. The changes of magnetic configuration responsible for this effect are studied, combining both magnetization and polarized neutron reflectivity measurements. The temperature is found to enhance the exchange-bias training effect as a result of the relaxation of an interface domain wall. The present study demonstrates that both temperature and cooling field may be used to tune the exchange field.
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75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions

Controlled domain wall injection into ferromagnetic nanowires from an optimized pad geometry

D. McGrouther, S. McVitie, J. N. Chapman, and A. Gentils

Appl. Phys. Lett. 91, 022506 (2007); http://dx.doi.org/10.1063/1.2753541 (3 pages) | Cited 22 times

Online Publication Date: 12 July 2007

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The authors present an improved geometry for a micron-scale pad for the injection of vortex domain walls (VDWs) into ferromagnetic nanowires. The pad supports a single vortex magnetization state, the chirality of which can be controlled simply by field saturation along a specific direction. We show, using Lorentz transmission electron microscopy, that utilization of such pads allows the chirality of VDWs injected into the attached wire to be predetermined. Furthermore, the pad vortex state is highly stable and survives repeated injection and depinning of VDWs from an asymmetric notch located some distance along the wire.
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75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys

Temperature increment in a current-heated nanowire for current-induced domain wall motion with finite thickness insulator layer

Chun-Yeol You and Seung-Seok Ha

Appl. Phys. Lett. 91, 022507 (2007); http://dx.doi.org/10.1063/1.2754351 (3 pages) | Cited 21 times

Online Publication Date: 12 July 2007

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The authors investigate the insulator-layer-thickness-dependent temperature increment in the nanowire for the current-induced domain wall motion. Practically, a finite thickness insulator layer must be placed between the semi-infinite substrate and the metallic nanowire for an electric insulation. Since a good electric insulator is also a thermal insulator, the temperature increment of the nanowire depends on the insulator layer’s thickness. An approximated analytic expression of the insulator thickness dependent temperature increment is obtained by employing the Fourier-transformed Green’s function method, and it is confirmed by the full numerical finite element method. The authors find that the control parameter of the temperature increment is the ratio between the insulator layer’s thickness and the nanowire’s width.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
73.63.Nm Quantum wires

Detecting dynamic signals of ideally ordered nanohole patterned disk media fabricated using nanoimprint lithography

Hirotaka Oshima, Hideyuki Kikuchi, Hiroshi Nakao, Ken-ichi Itoh, Takuya Kamimura, Takeshi Morikawa, Koji Matsumoto, Takahiro Umada, Hiroaki Tamura, Kazuyuki Nishio, and Hideki Masuda

Appl. Phys. Lett. 91, 022508 (2007); http://dx.doi.org/10.1063/1.2757118 (3 pages) | Cited 15 times

Online Publication Date: 13 July 2007

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The authors have fabricated ideally ordered alumina nanohole patterned disk media via anodic oxidation and nanoimprint lithography with a thermoplastic resist. The ordered arrays of alumina nanoholes with 100 nm pitch, filled with Co by electrodeposition, were created over a macroscopically large area on a hard-disk substrate using these industrially applicable nanofabrication technologies. Stable flight of a perpendicular magnetic head above the media and perpendicular magnetic anisotropy of the Co nanopillars enable high-speed dynamic magnetic recording and playback. Dynamic periodic signals that matched the nanopillar periodicity were clearly observed after writing bit patterns, showing alternate reversal of magnetization of the nanopillars.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.40.Hp Lithography, masks and pattern transfer

Fine structure in the tunneling characteristic of MgB2 thin films

R. Schneider, J. Geerk, A. G. Zaitsev, and H. v. Löhneysen

Appl. Phys. Lett. 91, 022509 (2007); http://dx.doi.org/10.1063/1.2755921 (3 pages) | Cited 4 times

Online Publication Date: 13 July 2007

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The authors report on the observation of theoretically predicted fine structures in the negative second derivative of the current-voltage characteristic measured on sandwich-type tunnel junctions on MgB2 thin films with a Tc of 35 K. The high resolution was achieved by a progress in the in situ preparation of MgB2 thin films by thermal evaporation of Mg combined with B sputtering. They were able to increase the substrate temperature up to 550 °C by sputtering boron from a red-hot sintered target. The film properties, such as Tc and the residual resistivity, significantly improved compared to films deposited at lower substrate temperatures. Better crystalline order within the MgB2 grains is evidently the key to the details of the electron-phonon coupling.
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74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.25.Kc Phonons
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.50.+r Tunneling phenomena; Josephson effects
81.15.Cd Deposition by sputtering
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