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16 Apr 2012

Volume 100, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 100, 164101 (2012); http://dx.doi.org/10.1063/1.3702579 (4 pages)

Cheol-Ho Yun, Leslie Y. Yeo, James R. Friend, and Bernard Yan
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Stability of spinmotive force in perpendicularly magnetized nanowires under high magnetic fields

Y. Yamane, J. Ieda, and S. Maekawa

Appl. Phys. Lett. 100, 162401 (2012); http://dx.doi.org/10.1063/1.4703933 (3 pages) | Cited 1 time

Online Publication Date: 16 April 2012

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Spinmotive force induced by domain wall motion in perpendicularly magnetized nanowires is numerically demonstrated. We show that using nanowires with large magnetic anisotropy can lead to a high stability of spinmotive force under strong magnetic fields. We observe spinmotive force in the order of tens of μV in a multilayered Co/Ni nanowire and several hundreds of μV in a L10-ordered FePt nanowire; the latter is two orders of magnitude greater than that in permalloy nanowires reported previously. The narrow structure and low mobility of a domain wall under magnetic fields in perpendicularly magnetized nanowires permits downsizing of spinmotive force devices.
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75.75.Fk Domain structures in nanoparticles
75.78.Fg Dynamics of domain structures
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Ba Spin polarized transport in metals

Co/Au multilayers with graded magnetic anisotropy for magnetic field sensing

M. Matczak, P. Kuświk, B. Szymański, M. Urbaniak, M. Schmidt, J. Aleksiejew, F. Stobiecki, and A. Ehresmann

Appl. Phys. Lett. 100, 162402 (2012); http://dx.doi.org/10.1063/1.4704176 (3 pages) | Cited 2 times

Online Publication Date: 17 April 2012

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A concept of a magnetoresistive sensor for magnetic fields based on a Au/Co-wedge/Au/Co/Au multilayer is proposed. The wedged Co layer is characterized by a laterally changing coercivity resulting from a gradient of perpendicular magnetic anisotropy. Its magnetization reversal in a perpendicular magnetic field takes place by movement of a single domain wall in the direction parallel to the anisotropy gradient. The magnetization reversal of the multilayer has been investigated by magnetooptical and magnetoresistive measurements. The resistance of the proposed film system correlates well with the position of the domain wall and thus it can be used to sense magnetic fields.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
72.15.Gd Galvanomagnetic and other magnetotransport effects
07.55.Ge Magnetometers for magnetic field measurements

Magnetoresistance and its relation to magnetization in Ni50Mn35Sn15 shape-memory epitaxial films

J. Dubowik, K. Załȩski, I. Gościańska, H. Głowiński, and A. Ehresmann

Appl. Phys. Lett. 100, 162403 (2012); http://dx.doi.org/10.1063/1.4704562 (4 pages)

Online Publication Date: 17 April 2012

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The magnetoresistance (MR) of Heusler alloy Ni50Mn35Sn15 epitaxial films on MgO substrates is studied as a function of temperature T and magnetic field H. The large negative MR extends over martensitic transformation with maximum of −22% at 110 K. In martensitic and austenitic phase, the MR is −3% and −5%, respectively. We show that the MR is governed mainly by magnetization paraprocess at high magnetic fields and scales as the square of magnetization Δm(H,T)2.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys

Reliable nucleation of isolated magnetic antivortices

Matthias Pues, Michael Martens, Thomas Kamionka, and Guido Meier

Appl. Phys. Lett. 100, 162404 (2012); http://dx.doi.org/10.1063/1.3698150 (3 pages) | Cited 1 time

Online Publication Date: 18 April 2012

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Individual magnetic antivortices are reliably generated in φ-shaped microstructures using a specific remagnetization sequence of in-plane fields. The process of antivortex creation is understood by means of micromagnetic simulations and is experimentally demonstrated by magnetic force microscopy on multiple microstructures. The probability of antivortex nucleation is optimized by the variation of the structure geometry and the nucleation field strength. The presented method opens the path to radio frequency absorption measurements which rely on the resonant excitation of an ensemble of antivortices.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.Cd Micromagnetic simulations
68.37.Rt Magnetic force microscopy (MFM)

NO-assisted molecular-beam epitaxial growth of nitrogen substituted EuO

R. Wicks, S. G. Altendorf, C. Caspers, H. Kierspel, R. Sutarto, L. H. Tjeng, and A. Damascelli

Appl. Phys. Lett. 100, 162405 (2012); http://dx.doi.org/10.1063/1.3701589 (4 pages)

Online Publication Date: 18 April 2012

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We have investigated a method for substituting oxygen with nitrogen in EuO thin films, which is based on molecular beam epitaxy distillation with NO gas as the oxidizer. By varying the NO gas pressure, we produce crystalline, epitaxial EuO1-xNx films with good control over the films’ nitrogen concentration. In situ x-ray photoemission spectroscopy reveals that nitrogen substitution is connected to the formation Eu3+4f6 and a corresponding decrease in the number of Eu2+4f7, indicating that nitrogen is being incorporated in its 3− oxidation state. While small amounts of Eu3+ in over-oxidized Eu1-δO thin films lead to a drastic suppression of the ferromagnetism, the formation of Eu3+ in EuO1-xNx still allows the ferromagnetic phase to exist with an unaffected Tc, thus providing an ideal model system to study the interplay between the magnetic f7 (J = 7/2) and the non-magnetic f6 (J = 0) states close to the Fermi level.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Spin-torque nano-emitters for magnonic applications

H. Ulrichs, V. E. Demidov, S. O. Demokritov, and S. Urazhdin

Appl. Phys. Lett. 100, 162406 (2012); http://dx.doi.org/10.1063/1.4704563 (4 pages) | Cited 2 times

Online Publication Date: 19 April 2012

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In the emerging field of magnonics, spin waves are utilized as a medium for high-speed transmission and processing of electrical signals on the nanometer scale. The implementation of high-performance magnonic devices requires efficient nano-scaled sources of spin waves. Here, we demonstrate experimentally that this goal can be accomplished by utilizing a modified design of spin-torque devices, in which the internal dipolar field is compensated in the active device area by a built-in micromagnet. We show experimentally that the proposed device geometry enables efficient emission of spin waves with a large propagation length for practical implementation of integrated magnonic circuits.
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85.70.Ay Magnetic device characterization, design, and modeling
84.40.-x Radiowave and microwave (including millimeter wave) technology

Collective spin waves in a bicomponent two-dimensional magnonic crystal

G. Gubbiotti, S. Tacchi, M. Madami, G. Carlotti, S. Jain, A. O. Adeyeye, and M. P. Kostylev

Appl. Phys. Lett. 100, 162407 (2012); http://dx.doi.org/10.1063/1.4704659 (5 pages) | Cited 4 times

Online Publication Date: 19 April 2012

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Spin waves propagating in a bicomponent magnonic crystal consisting of a two-dimensional array of alternated NiFe and Co nanodots have been investigated. The frequency dispersion of collective modes, measured by Brillouin light scattering, is compared with the band diagram obtained by numerically solving the eigenvalue problem derived from the linearized Landau-Lifshitz magnetic torque equation. It is shown that the modes which are active in Brillouin experiment are characterized by the simplest modal profiles within the NiFe dots. For such excitations, the Co dots act as mediators of dipole coupling between the NiFe dots.
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75.30.Ds Spin waves
75.50.Tt Fine-particle systems; nanocrystalline materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering
75.75.-c Magnetic properties of nanostructures

Lateral spin transport through bulk silicon

Jing Li and Ian Appelbaum

Appl. Phys. Lett. 100, 162408 (2012); http://dx.doi.org/10.1063/1.4704802 (3 pages) | Cited 2 times

Online Publication Date: 19 April 2012

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Using ballistic hot electron techniques, we demonstrate lateral spin transport through a bulk Si wafer. Despite a wide spin transport time distribution caused by transport path variation in the 400 μm-thick Si channel, the absence of a buried interface in close proximity increases the observed spin lifetime to approximately 100 ns at 61 K. The relative insensitivity of this lifetime to temperature variation (and its absolute magnitude) indicates a contribution from an extrinsic depolarization mechanism such as disorder and defects at the exposed air/Si interface in the transport region between injector and detector.
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72.25.Dc Spin polarized transport in semiconductors
72.80.Cw Elemental semiconductors
73.23.Ad Ballistic transport

Spin-dependent tunneling transport in a ferromagnetic GaMnAs and un-doped GaAs double-quantum-well heterostructure

Iriya Muneta, Shinobu Ohya, and Masaaki Tanaka

Appl. Phys. Lett. 100, 162409 (2012); http://dx.doi.org/10.1063/1.4704154 (3 pages)

Online Publication Date: 20 April 2012

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We investigate the spin-dependent tunneling transport in a ferromagnetic GaMnAs and un-doped GaAs double-quantum-well heterostructure. Clear tunneling magnetoresistance (TMR) and negative differential resistance due to the strong resonant tunneling in the GaAs quantum well (QW) are demonstrated in this device. We show that TMR oscillates as a function of the bias voltage following the dI/dV-V characteristics, and TMR becomes negative at biases where resonant tunneling occurs. These results can be explained by the difference of the potential drops in the magnetic tunnel junction composed of the top GaMnAs/AlAs/GaMnAs-QW between parallel and anti-parallel magnetization.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Pq Other materials
75.50.Dd Nonmetallic ferromagnetic materials
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FeNi-based magnetoimpedance multilayers: Tailoring of the softness by magnetic spacers

A. V. Svalov, E. Fernandez, A. Garcia-Arribas, J. Alonso, M. L. Fdez-Gubieda, and G. V. Kurlyandskaya

Appl. Phys. Lett. 100, 162410 (2012); http://dx.doi.org/10.1063/1.4704984 (4 pages) | Cited 3 times

Online Publication Date: 20 April 2012

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The microstructure and magnetic properties of sputtered permalloy films and FeNi(170 nm)/X/FeNi(170 nm) (X = Co, Fe, Gd, Gd-Co) sandwiches were studied. Laminating of the thick FeNi film with various spacers was done in order to control the magnetic softness of FeNi-based multilayers. In contrast to the Co and Fe spacers, Gd and Gd-Co magnetic spacers improved the softness of the FeNi/X/FeNi sandwiches. The magnetoimpedance responses were measured for [FeNi/Ti(6 nm)]2/FeNi and [FeNi/Gd(2 nm)]2/FeNi multilayers in a frequency range of 1–500 MHz: for all frequencies under consideration the highest magnetoimpedance variation was observed for [FeNi/Gd(2 nm)]2/FeNi multilayers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
61.72.-y Defects and impurities in crystals; microstructure
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