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16 Aug 2010

Volume 97, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 073101 (2010); http://dx.doi.org/10.1063/1.3478515 (3 pages)

Hon-Way Lin (林弘偉), Yu-Jung Lu (呂宥蓉), Hung-Ying Chen (陳虹穎), Hong-Mao Lee (李弘貿), and Shangjr Gwo (果尚志)
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Linear correlation between uncompensated antiferromagnetic spins and exchange bias in Mn–Ir/Co100−xFex bilayers

Masakiyo Tsunoda, Hirokazu Takahashi, Tetsuya Nakamura, Chiharu Mitsumata, Shinji Isogami, and Migaku Takahashi

Appl. Phys. Lett. 97, 072501 (2010); http://dx.doi.org/10.1063/1.3479500 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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A correlation between uncompensated (UC) antiferromagnetic (AF) spins and exchange bias (EB) strength was investigated for Mn74Ir26/Co100−xFex bilayers. The EB strength had a maximum at x = 25 at. %, and the x-ray magnetic circular dichroism of Mn, representing the UC-AF spins, changed systematically in sign and magnitude with respect to x. A linear correlation was found between the EB strength and the root mean square magnitude of the UC-Mn spins. The hidden parameter connecting these two quantities might be exchange coupling energy at the heterointerface, which varies as a function of the ferromagnetic layer composition.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions

Strong effects of magnetic anisotropy on exchange coupling and magnetotransport properties of ferromagnetic/NiO/ferromagnetic trilayers

X. H. Liu, W. Liu, S. Guo, W. J. Gong, J. N. Feng, and Z. D. Zhang

Appl. Phys. Lett. 97, 072502 (2010); http://dx.doi.org/10.1063/1.3480418 (3 pages) | Cited 2 times

Online Publication Date: 16 August 2010

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Strong effects of the magnetic anisotropy on the exchange coupling are observed in FM1/NiO(6 nm)/FM2 trilayers with ferromagnetic (FM) layers Co or Fe. Different magnetic properties are found for Co/NiO/Fe and Fe/NiO/Co trilayers with Ag sublayer and cover layer. The Ag sublayer strongly affects the magnetic anisotropy of FM/antiferromagnetic (FM/AF) bilayers and further influences the exchange coupling in FM1/NiO/FM2 trilayers. In particular, the sign of the magnetoresistance changes from negative after zero-field cooling to positive after field cooling, which is due to a reversal of the Co spin polarization. Furthermore, the interfacial coupling between FM and NiO enhances the blocking temperature of NiO.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
72.25.Mk Spin transport through interfaces

Magnetic anisotropies of laterally confined structures of epitaxial Fe films on GaAs (001)

K. K. Meng, J. Lu, S. L. Wang, H. J. Meng, J. H. Zhao, J. Misuraca, P. Xiong, and S. von Molnár

Appl. Phys. Lett. 97, 072503 (2010); http://dx.doi.org/10.1063/1.3480423 (3 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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We have investigated magnetic properties of laterally confined structures of epitaxial Fe films on GaAs (001). Fe films with different thicknesses were grown by molecular-beam epitaxy and patterned into regular arrays of rectangles with varying aspect ratios. In-plane magnetic anisotropy was observed in all of the patterned Fe films both at 15 and 300 K. We have demonstrated that the coercive fields can be tuned by varying the aspect ratios of the structures. The magnitudes of the corresponding anisotropy constants have been determined and the shape anisotropy constant is found to be enhanced as the aspect ratio is increased.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.at Other materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.30.Gw Magnetic anisotropy

Influence of magnetic substrate in the transport critical current of superconducting tapes

Alvaro Sanchez, Nuria Del-Valle, Carles Navau, and Du-Xing Chen

Appl. Phys. Lett. 97, 072504 (2010); http://dx.doi.org/10.1063/1.3481082 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2010

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An important effect on the critical-current density Jc in a superconducting tape is found when the tape is above a soft ferromagnetic substrate, as is the case with many coated conductors. Here, a model is presented to analyze the complex magnetic interaction between the induced currents in the superconductor and the poles in the magnet. We find that transport Jc decreases at nonzero applied fields when there is a magnetic substrate and this reduction can be controlled by changing the magnet thickness. The model presented here can, therefore, become a useful tool for understanding and optimizing superconductor-magnet systems.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents

Electron microscopy of GaAs/MnAs core/shell nanowires

N. S. Dellas, J. Liang, B. J. Cooley, N. Samarth, and S. E. Mohney

Appl. Phys. Lett. 97, 072505 (2010); http://dx.doi.org/10.1063/1.3481066 (3 pages) | Cited 2 times

Online Publication Date: 18 August 2010

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GaAs/MnAs core/shell nanowire heterostructures were synthesized by catalyst-free molecular beam epitaxy. Transmission electron microscopy (TEM) reveals that the GaAs core predominantly grows with the zinc-blende crystal structure with a [111] growth direction. In a small population of wires, the crystal structure transitions from zinc blende to wurtzite with a [001] growth direction. Cross-sectional TEM shows that the MnAs grows epitaxially on the GaAs core in the NiAs prototype structure with an epitaxial relation of [20math1] MnAs∥[111]GaAs and (01math0) MnAs∥GaAs (math10). When the GaAs core is in the wurtzite structure, the epitaxial relation between the GaAs and MnAs changes to [0001] MnAs∥[0001]GaAs and (math2math0) MnAs∥(math2math0)GaAs.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Gf Nanowires
81.07.Vb Quantum wires
68.55.A- Nucleation and growth
61.66.Fn Inorganic compounds
81.05.Ea III-V semiconductors

Homologous series of iron pnictide oxide superconductors (Fe2As2)[Can+1(Sc,Ti)nOy] (n = 3,4,5) with extremely thick blocking layers

Hiraku Ogino, Shinya Sato, Kohji Kishio, Jun-ichi Shimoyama, Tetsuya Tohei, and Yuichi Ikuhara

Appl. Phys. Lett. 97, 072506 (2010); http://dx.doi.org/10.1063/1.3478850 (3 pages) | Cited 25 times

Online Publication Date: 18 August 2010

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We have discovered homologous series of iron pnictide superconductors (Fe2As2)[Can+1(Sc,Ti)nOy] (n = 3,4,5). These compounds have extremely thick blocking layers up to quintuple perovskite layers sandwiched by the Fe2As2 layers. These samples exhibited bulk superconductivity with relatively high Tc up to 42 K. The relationship between Tc and the iron-plane interlayer distance suggested that Tc of the iron based superconductor is basically determined by the local structure of Fe2As2 layer.
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74.78.Fk Multilayers, superlattices, heterostructures
74.81.-g Inhomogeneous superconductors and superconducting systems, including electronic inhomogeneities
74.10.+v Occurrence, potential candidates

Tuning of current-induced domain wall resonance frequency using Gd doping

S. Lepadatu, J. S. Claydon, D. Ciudad, C. J. Kinane, S. Langridge, S. S. Dhesi, and C. H. Marrows

Appl. Phys. Lett. 97, 072507 (2010); http://dx.doi.org/10.1063/1.3481074 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2010

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The current-induced resonance frequencies of domain walls in parabolic pinning potentials are measured in Gd doped NiFe as a function of doping level. The modification of magnetic properties due to Gd doping results in an order of magnitude increase in resonance frequencies for 10% Gd doping, due to the induced out-of-plane anisotropy, and the resonance frequencies are excited at lower current densities compared to undoped NiFe. These results are reproduced using a one-dimensional model of domain wall resonance, and found to be in good agreement in the small oscillation amplitude limit.
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75.60.Ch Domain walls and domain structure
61.72.U- Doping and impurity implantation
75.30.Gw Magnetic anisotropy

Experimental exploration of the origin of magnetostriction in single crystalline iron

Q. Xing, T. A. Lograsso, M. P. Ruffoni, C. Azimonte, S. Pascarelli, and D. J. Miller

Appl. Phys. Lett. 97, 072508 (2010); http://dx.doi.org/10.1063/1.3481083 (3 pages) | Cited 3 times

Online Publication Date: 19 August 2010

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The magnetostrictive atomic strain in a pure Fe single crystal was measured by differential x-ray absorption spectroscopy. The obtained tetragonal magnetostriction constant, (3/2)λ100, was determined to be 45 ppm, consistent with the previously reported theoretical value calculated from a spin-orbit coupling theory. These results provide a foundation for understanding the origin of magnetostriction in pure Fe as well as Fe-based binary alloys.
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75.80.+q Magnetomechanical effects, magnetostriction
71.70.Ch Crystal and ligand fields
78.70.Dm X-ray absorption spectra
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Millimeter wave phase shifter based on ferromagnetic resonance in a hexagonal barium ferrite thin film

Zihui Wang, Young-Yeal Song, Yiyan Sun, Joshua Bevivino, Mingzhong Wu, V. Veerakumar, Timothy J. Fal, and Robert E. Camley

Appl. Phys. Lett. 97, 072509 (2010); http://dx.doi.org/10.1063/1.3481086 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2010

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A hexagonal ferrite thin film-based planar millimeter-wave phase shifter was demonstrated. The device made use of an M-type barium ferrite (BaM) thin film prepared by pulsed laser deposition and a coplanar waveguide geometry. The phase tuning relied on ferromagnetic resonance in the BaM film. The device showed a phase tuning rate of 43°/(mm kOe) and an insertion loss of 3.1 dB/mm in the on-resonance regime. In off-resonance regimes, the device showed smaller loss and smaller tuning rates. The experimental results were confirmed by theoretical calculations.
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85.70.Ge Ferrite and garnet devices
84.40.Dc Microwave circuits
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Gg Ferrimagnetics
81.16.Mk Laser-assisted deposition

Domain wall assisted magnetization switching in (111) oriented L10 FePt grown on a soft magnetic metallic glass

Neelam Kaushik, Parmanand Sharma, Kunio Yubuta, Akihiro Makino, and Akihisa Inoue

Appl. Phys. Lett. 97, 072510 (2010); http://dx.doi.org/10.1063/1.3479054 (3 pages) | Cited 1 time

Online Publication Date: 19 August 2010

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We report on growth and magnetic properties of exchange-coupled (111)-L10 FePt hard/CoFeTaB soft magnetic metallic glass bilayered structure processed at lower temperature ( ∼ 400 °C). Single phaselike hysteresis loops with tailorable coercivity (<8.2 kOe) in out of plane direction are obtained. The magnetization switching mechanism is identified as domain wall assisted. In views of excellent nanofabrication abilities of metallic glass thin film and the ability to grow preferred oriented L10 FePt, the present bilayered structure is very promising for the fabrication of high density bit—patterned magnetic recording media and other spintronic devices.
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81.05.Kf Glasses (including metallic glasses)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.50.Ww Permanent magnets
75.50.Kj Amorphous and quasicrystalline magnetic materials
68.55.A- Nucleation and growth

Ferromagnetic resonance in double perovskite epitaxial thin films of La2NiMnO6 on SrTiO3 and NdGaO3 substrates

S. Kazan, F. A. Mikailzade, M. Özdemir, B. Aktaş, B. Rameev, A. Intepe, and A. Gupta

Appl. Phys. Lett. 97, 072511 (2010); http://dx.doi.org/10.1063/1.3481678 (3 pages) | Cited 3 times

Online Publication Date: 19 August 2010

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Ferromagnetic resonance (FMR) studies of epitaxial La2NiMnO6 (LNMO) thin films on (100) oriented SrTiO3 and (110) oriented NdGaO3 substrates at room temperature are presented. Observation of FMR spectra above the Curie temperature of this compound confirms the presence of magnetic ordering in LNMO thin films at room temperature. Best fitting of FMR spectra has been made on the assumption of the coexistence of two magnetic phases with different easy and hard axis periodicities in the film plane of LNMO. The spectra of the films on various substrates are characterized by different in-plane and out-of-plane symmetries, which indicates the existence of different epitaxial growth on the substrates with different crystal symmetries and orientations.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
68.55.J- Morphology of films

Vortex nucleation in spin-torque nanocontact oscillators

T. Devolder, Joo-Von Kim, M. Manfrini, W. van Roy, L. Lagae, and C. Chappert

Appl. Phys. Lett. 97, 072512 (2010); http://dx.doi.org/10.1063/1.3478843 (3 pages) | Cited 2 times

Online Publication Date: 20 August 2010

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We present an experimental study of the nucleation rate associated with current-driven vortex oscillations in magnetic nanocontacts. We find that the nucleation and subsequent steady-state oscillation of a vortex can be initiated using current pulses as short as a few nanoseconds, yielding instant on oscillator capability. The nucleation rate is governed by an Arrhenius law, with an exponential dependence on the applied current magnitude. The mechanism for the vortex nucleation is discussed and compared to analytical estimates assuming the transient presence of a vortex-antivortex pair.
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75.75.-c Magnetic properties of nanostructures
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Tunnel magnetoresistance and spin torque switching in MgO-based magnetic tunnel junctions with a Co/Ni multilayer electrode

Takahiro Moriyama, Theodore J. Gudmundsen, Pinshane Y. Huang, Luqiao Liu, David A. Muller, Daniel C. Ralph, and Robert A. Buhrman

Appl. Phys. Lett. 97, 072513 (2010); http://dx.doi.org/10.1063/1.3481798 (3 pages) | Cited 3 times

Online Publication Date: 20 August 2010

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We have fabricated MgO-barrier magnetic tunnel junctions with a Co/Ni switching layer to reduce the demagnetizing field via interface anisotropy. With a fcc-(111) oriented Co/Ni multilayer combined with an FeCoB insertion layer, the demagnetizing field is 2 kOe and the tunnel magnetoresistance can be as high as 106%. Room-temperature measurements of spin-torque switching are in good agreement with predictions for a reduced critical current associated with the small demagnetization for antiparallel-to-parallel switching. For parallel-to-antiparallel switching the small demagnetization field causes spatially nonuniform reversal nucleated at the sample ends, with a low energy barrier but a higher switching current.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.-d Domain effects, magnetization curves, and hysteresis
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