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7 Mar 2011

Volume 98, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 98, 104101 (2011); http://dx.doi.org/10.1063/1.3560505 (3 pages)

Zhongchang Wang, Susumu Tsukimoto, Rong Sun, Mitsuhiro Saito, and Yuichi Ikuhara
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Micromagnetic study of switching boundary of a spin torque nanodevice

Yan Zhou, Johan Åkerman, and Jonathan Z. Sun

Appl. Phys. Lett. 98, 102501 (2011); http://dx.doi.org/10.1063/1.3561753 (3 pages) | Cited 3 times

Online Publication Date: 7 March 2011

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We report on a numerical study of the micromagnetic switching process of a nanostructured spin torque device. We show that incoherent spin waves can be excited over a wide range of current and field even at zero temperature. These large amplitude, incoherent, and nonzero k spin wave modes are shown to alter the switching phase boundary from that calculated within a macrospin model. The presence of telegraphic transitions between different spin wave modes may also contribute to the so-called back-hopping phenomenon where the switching probability varies nonmonotonically with increasing bias current.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Evidence of hydrogen-mediated ferromagnetic coupling in Mn-doped ZnO

Jun Kue Park, Kyu Won Lee, Hyocheon Kweon, and Cheol Eui Lee

Appl. Phys. Lett. 98, 102502 (2011); http://dx.doi.org/10.1063/1.3561775 (3 pages) | Cited 10 times

Online Publication Date: 7 March 2011

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Hydrogen shallow donors in undoped and doped ZnO systems have been studied by means of the electron paramagnetic resonance and nuclear magnetic resonance measurements. Experimental evidence is given in this work for coupling of hydrogen shallow donors and Mn ions in Mn-doped ZnO mediating short-range ferromagnetic spin-spin interaction.
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71.55.Gs II-VI semiconductors
76.30.Lh Other ions and impurities
76.60.-k Nuclear magnetic resonance and relaxation
75.50.Dd Nonmetallic ferromagnetic materials

Influence of GaAs surface structure on tunneling anisotropic magnetoresistance and magnetocrystalline anisotropy in epitaxial Co50Fe50/n-GaAs junctions

Tetsuya Uemura, Masanobu Harada, Takafumi Akiho, Ken-ichi Matsuda, and Masafumi Yamamoto

Appl. Phys. Lett. 98, 102503 (2011); http://dx.doi.org/10.1063/1.3561759 (3 pages) | Cited 5 times

Online Publication Date: 8 March 2011

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An epitaxial Co50Fe50 layer was grown on As-terminated or Ga-terminated GaAs, and the influence of the termination species on both uniaxial-type tunneling anisotropic magnetoresistance (TAMR) characteristics and magnetocrystalline anisotropy was investigated. The magnetocrystalline anisotropy induced in the Co50Fe50 thin film was strongly dependent on the termination species of the GaAs surface, while the TAMR characteristics were almost unchanged. These experimental findings suggest that the TAMR effect is due to the anisotropy of electronic structure rather than the structural anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
68.55.A- Nucleation and growth
75.50.Bb Fe and its alloys

Improving the performance of superconducting microwave resonators in magnetic fields

D. Bothner, T. Gaber, M. Kemmler, D. Koelle, and R. Kleiner

Appl. Phys. Lett. 98, 102504 (2011); http://dx.doi.org/10.1063/1.3560480 (3 pages) | Cited 2 times

Online Publication Date: 8 March 2011

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The operation of superconducting coplanar waveguide cavities, as used for circuit quantum electrodynamics and kinetic inductance detectors, in perpendicular magnetic fields normally leads to a reduction in the device performance due to energy dissipating Abrikosov vortices. We experimentally investigate the vortex induced energy losses in such Nb resonators with different spatial distributions of micropatterned pinning sites (antidots) by transmission spectroscopy measurements at 4.2 K. In comparison to resonators without antidots we find a significant reduction in vortex induced losses, and thus increased quality factors over a broad range of frequencies and applied powers in moderate fields.
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84.40.Az Waveguides, transmission lines, striplines
85.25.Am Superconducting device characterization, design, and modeling

Optimization of the refrigerant capacity in multiphase magnetocaloric materials

R. Caballero-Flores, V. Franco, A. Conde, K. E. Knipling, and M. A. Willard

Appl. Phys. Lett. 98, 102505 (2011); http://dx.doi.org/10.1063/1.3560445 (3 pages) | Cited 14 times

Online Publication Date: 9 March 2011

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The refrigerant capacity (RC) of magnetocaloric materials can be enhanced using multiphase materials or composites, which expand the temperature range over which a significant magnetic entropy change can be obtained. Numerical simulations show that by controlling the parameters of the composite (the fraction of the different phases and their Curie temperatures) improvements of RC of ∼ 83% are possible. The maximum applied field plays a crucial, nonmonotonic, role in the optimization. As a proof of concept, it is shown that the combination of two Fe88−2xCoxNixZr7B4Cu1 alloys produces an enhancement in RC of ∼ 37%, making it ∼ 92% larger than that of Gd5Si2Ge1.9Fe0.1.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Mg Numerical simulation studies

Preparation of ferroelectric field effect transistor based on sustainable strongly correlated (Fe,Zn)3O4 oxide semiconductor and their electrical transport properties

Junichi Takaobushi, Teruo Kanki, Tomoji Kawai, and Hidekazu Tanaka

Appl. Phys. Lett. 98, 102506 (2011); http://dx.doi.org/10.1063/1.3564885 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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We have constructed a field effect transistor structure composed of the sustainable oxide semiconductor (Fe,Zn)3O4 with high Curie temperature and ferroelectric Pb(Zr,Ti)O3. Electric field control of (Fe2.5Zn0.5)O4 channel resistance was achieved in the heterostructures though modulation of their carrier concentration. The results will lead to the significant development of sustainable oxide semiconductor spintronics devices working at room temperature.
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85.30.Tv Field effect devices
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Spin and orbital magnetic moments of molecular beam epitaxy γ′-Fe4N films on LaAlO3(001) and MgO(001) substrates by x-ray magnetic circular dichroism

K. Ito, G. H. Lee, K. Harada, M. Suzuno, T. Suemasu, Y. Takeda, Y. Saitoh, M. Ye, A. Kimura, and H. Akinaga

Appl. Phys. Lett. 98, 102507 (2011); http://dx.doi.org/10.1063/1.3564887 (3 pages) | Cited 5 times

Online Publication Date: 10 March 2011

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10-nm-thick γ′-Fe4N films were grown epitaxially on LaAlO3(001) and MgO(001) substrates by molecular beam epitaxy using solid Fe and a radio-frequency NH3 plasma. The lattice mismatch of these substrates to γ′-Fe4N is 0% and 11%, respectively. Spin and orbital magnetic moments of these γ′-Fe4N epitaxial films were deduced by x-ray magnetic circular dichroism measurements at 300 K. The total magnetic moments are almost the same for the two substrates, that is, 2.44±0.06 μB and 2.47±0.06 μB, respectively. These values are very close to those predicted theoretically, and distinctively larger than that for α-Fe.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
78.66.Nk Insulators
78.20.Ls Magneto-optical effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Modeling bond dilutions in Josephson junction arrays

Jian-Ping Lv and Qing-Hu Chen

Appl. Phys. Lett. 98, 102508 (2011); http://dx.doi.org/10.1063/1.3564891 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2011

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Using resistivity-shunted-junction dynamics, we model bond dilutions in Josephson junction arrays. The current-voltage characteristics are obtained by large-scale numerical simulations. By dynamic scaling analysis to the finite-temperature phase transition, we provide clear evidence for the existence of non-Kosterlitz–Thouless-type phase transition, as described by Kosterlitz et al. [J. Phys. C 6, 1181 (1973) ; J. Phys. C 7, 1046 (1974)] in a wide range of disorder strengths. Critical temperature and exponents of the phase transitions are estimated, which are further confirmed by the finite-size scaling analysis at the transition temperature.
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74.50.+r Tunneling phenomena; Josephson effects
74.62.-c Transition temperature variations, phase diagrams

Deep subnanosecond spin torque switching in magnetic tunnel junctions with combined in-plane and perpendicular polarizers

G. E. Rowlands, T. Rahman, J. A. Katine, J. Langer, A. Lyle, H. Zhao, J. G. Alzate, A. A. Kovalev, Y. Tserkovnyak, Z. M. Zeng, H. W. Jiang, K. Galatsis, Y. M. Huai, P. Khalili Amiri, K. L. Wang, et al.

Appl. Phys. Lett. 98, 102509 (2011); http://dx.doi.org/10.1063/1.3565162 (3 pages) | Cited 14 times

Online Publication Date: 10 March 2011

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We show that adding a perpendicular polarizer to a conventional spin torque memory element with an in-plane free layer and an in-plane polarizer can significantly increase the write speed and decrease the write energy of the element. We demonstrate the operation of such spin torque memory elements with write energies of 0.4 pJ and write times of 0.12 ns.
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75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Multiferroic response to magnetic field in orthorhombic manganites

M. H. Qin, Y. M. Tao, S. Dong, H. B. Zhao, X. S. Gao, and J.-M. Liu

Appl. Phys. Lett. 98, 102510 (2011); http://dx.doi.org/10.1063/1.3565241 (3 pages) | Cited 4 times

Online Publication Date: 10 March 2011

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The magnetoelectric coupling in Eu0.55Y0.45MnO3 is studied based on a microscopic spin model which includes the superexchange interaction, the single-ion anisotropy, the Dzyaloshinskii–Moriya interaction, and the cubic anisotropy. Our Monte Carlo simulation reproduces the experimentally observed multiferroic response to magnetic field B. It is demonstrated that the magnetic field can control the multiferroic behaviors by modulating the spin arrangements, leading to various flops of electric polarization. In addition, an interesting state in which both the electric polarizations along the a-axis and c-axis are activated under high B is predicted and discussed.
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75.85.+t Magnetoelectric effects, multiferroics
75.30.Et Exchange and superexchange interactions
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw Magnetic anisotropy
77.22.Ej Polarization and depolarization

Observation of magnetic domain structures in epitaxial MnAs film on GaAs(001) with temperature hysteresis

JinBae Kim, Hiro Akinaga, and Jongryoul Kim

Appl. Phys. Lett. 98, 102511 (2011); http://dx.doi.org/10.1063/1.3564900 (3 pages) | Cited 2 times

Online Publication Date: 11 March 2011

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The saturation magnetization of MnAs films epitaxially grown on GaAs(001) substrates exhibited temperature hysteresis in the temperature range of 10–45 °C. We investigated the cause of the temperature hysteresis using temperature- and field-controlled magnetic force microscopy (MFM). The MFM results showed that inside the ferromagnetic α-MnAs stripes of the film at 30 °C, 180° domains were formed during cooling but a single domain state was developed during heating. Despite the cooling procedure, a single domain state was found inside the α-MnAs stripes when a magnetic field of 800 Oe was applied. From these results, the spontaneous magnetization of the α-MnAs phase was ascribed to the temperature hysteresis.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Tunable magnetic domain wall oscillator at an anisotropy boundary

J. H. Franken, R. Lavrijsen, J. T. Kohlhepp, H. J. M. Swagten, and B. Koopmans

Appl. Phys. Lett. 98, 102512 (2011); http://dx.doi.org/10.1063/1.3562299 (3 pages) | Cited 4 times

Online Publication Date: 11 March 2011

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We propose a magnetic domain wall (DW) oscillator scheme, in which a low dc current excites gigahertz angular precession of a DW at a fixed position. The scheme consists of a DW pinned at a magnetic anisotropy step in a perpendicularly magnetized nanostrip. The frequency is tuned by the current flowing through the strip. A perpendicular external field tunes the critical current density needed for precession, providing great experimental flexibility. We investigate this system using a simple one-dimensional model and full micromagnetic calculations. This oscillating nanomagnet is relatively easy to fabricate and could find application in future nanoscale microwave sources.
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75.60.Ch Domain walls and domain structure
75.75.Fk Domain structures in nanoparticles
75.30.Gw Magnetic anisotropy
75.78.Cd Micromagnetic simulations

Decoupling mechanisms and magnetic stability of nanostructured iron chains prepared by sputtering

F. Jiménez-Villacorta, E. Céspedes, C. Ocal, and C. Prieto

Appl. Phys. Lett. 98, 102513 (2011); http://dx.doi.org/10.1063/1.3559918 (3 pages) | Cited 2 times

Online Publication Date: 11 March 2011

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Nanostructured Fe/Fe-oxide systems with a chain morphology formed by interconnected metallic clusters were prepared by sputtering at very low substrate temperatures. The effect of the in situ controlled oxidation at low temperature leads to an effective decoupling of the particles forming the chains, which is attributed to a physical separation of particles through formation of a core-shell metal-oxide structure. In contrast, samples oxidized at room conditions exhibit features of strongly correlated particle systems, in which magnetic decoupling and stabilization can be explained within the framework of the random anisotropy model by considering the effect of the oxide phase.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
75.50.Tt Fine-particle systems; nanocrystalline materials

Structural-induced antiferromagnetism in Mn-based full Heusler alloys: The case of Ni2MnAl

I. Galanakis and E. Şaşıoğlu

Appl. Phys. Lett. 98, 102514 (2011); http://dx.doi.org/10.1063/1.3565246 (3 pages) | Cited 6 times

Online Publication Date: 11 March 2011

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We employ ab initio electronic structure calculations and a model Heisenberg Hamiltonian, and show that the Heusler alloy Ni2MnAl exhibits a ferrromagnetic–antiferromagnetic phase transition upon Mn–Al disorder. The transition is triggered by the smaller Mn–Mn nearest-neighbors distance in accordance to the Bethe–Slater curve. Our results explain available experimental data and show that the prevention of disorder is essential to achieve maximum performance in Heusler-based devices.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
75.10.Jm Quantized spin models, including quantum spin frustration
71.15.-m Methods of electronic structure calculations
75.50.Ee Antiferromagnetics
71.20.Be Transition metals and alloys

Fe/Cr substitution in MnAs compound: Increase in the relative cooling power

C. Salazar Mejía, A. M. Gomes, M. S. Reis, and D. L. Rocco

Appl. Phys. Lett. 98, 102515 (2011); http://dx.doi.org/10.1063/1.3560309 (3 pages) | Cited 1 time

Online Publication Date: 11 March 2011

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We improved the magnetocaloric potential of MnAs compounds by stoichiometry decrease in Mn through small substitution by Fe and Cr. Isothermal magnetization measurements present hysteresis with metamagnetic processes near the transition temperature, indicating a coexistence of magnetic phases. Magnetic entropy change and the adiabatic temperature change were obtained from heat capacity measurements up to 380 K at magnetic fields of 0 and 5 T. The results show high values of the magnetocaloric properties, as the relative cooling power, even in the presence of the hysteresis. The results can be associated to an increase in chemical pressure by Fe/Cr.
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75.30.Sg Magnetocaloric effect, magnetic cooling
61.66.Bi Elemental solids
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.gd Entropy
65.40.Ba Heat capacity
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
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