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12 Oct 2009

Volume 95, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 95, 153101 (2009); http://dx.doi.org/10.1063/1.3244597 (3 pages)

Geunjae Kwak, Mikyung Lee, Karuppanan Senthil, and Kijung Yong
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Modeling spin transport with current-sensing spin detectors

Jing Li and Ian Appelbaum

Appl. Phys. Lett. 95, 152501 (2009); http://dx.doi.org/10.1063/1.3241080 (3 pages) | Cited 1 time

Online Publication Date: 12 October 2009

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By incorporating the proper boundary conditions, we analytically derive the impulse response (or “Green’s function”) of a current-sensing spin detector. We also compare this result to a Monte Carlo simulation (which automatically takes the proper boundary condition into account) and an empirical spin transit time distribution obtained from experimental spin precession measurements. In the strong drift-dominated transport regime, this spin current impulse response can be approximated by multiplying the spin density impulse response by the average drift velocity. However, in weak drift fields, large modeling errors up to a factor of 3 in most-probable spin transit time can be incurred unless the full spin current Green’s function is used.
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72.25.Pn Current-driven spin pumping
75.30.Ds Spin waves

Epitaxial-strain effect on charge/orbital order in Pr0.5Ca0.5MnO3 films

D. Okuyama, M. Nakamura, Y. Wakabayashi, H. Itoh, R. Kumai, H. Yamada, Y. Taguchi, T. Arima, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 95, 152502 (2009); http://dx.doi.org/10.1063/1.3246158 (3 pages) | Cited 13 times

Online Publication Date: 12 October 2009

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Effect of growth orientation on charge- and orbital-ordering (CO-OO) phenomena has been studied for Pr0.5Ca0.5MnO3 epitaxial thin films fabricated on (LaAlO3)0.3–(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates by means of resistivity, synchrotron x-ray diffraction, and polarized optical microscopy measurements. CO-OO transition is observed around 220 K for a film grown on an LSAT (011) substrate [(011) film], similarly to a bulk sample, while a film grown on a (001) plane of LSAT [(001) film] shows much higher transition temperature around 300 K. The domain size of OO is approximately three times as large in the (011) film as in the (001) film. These results demonstrate that various properties of CO-OO phenomena can be controlled with the growth orientation via the epitaxial strain from the substrate.
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73.61.Ng Insulators
68.55.aj Insulators

Ni–Mn–In–Co single-crystalline particles for magnetic shape memory composites

Jian Liu, Nils Scheerbaum, Sandra Weiß, and Oliver Gutfleisch

Appl. Phys. Lett. 95, 152503 (2009); http://dx.doi.org/10.1063/1.3249585 (3 pages) | Cited 6 times

Online Publication Date: 13 October 2009

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Single- and oligo-crystalline magnetic shape memory (MSM) Ni45.2Mn36.7In13Co5.1 particles were prepared by mechanical grinding the melt-spun ribbons. The influence of annealing and grinding on the crystal structure and magnetic properties of the ribbons and particles was systematically investigated. The obtained Ni45.2Mn36.7In13Co5.1 single-crystalline particles exhibit a field-induced martensitic transformation above room temperature, thus are used for MSM-polyester composites.
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81.30.Kf Martensitic transformations
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions

Magnetism of single-crystalline Co nanorods

K. Soulantica, F. Wetz, J. Maynadié, A. Falqui, R. P. Tan, T. Blon, B. Chaudret, and M. Respaud

Appl. Phys. Lett. 95, 152504 (2009); http://dx.doi.org/10.1063/1.3237157 (3 pages) | Cited 8 times

Online Publication Date: 13 October 2009

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We report on the synthesis and preparation of oriented nanomaterials of single crystalline metallic Co nanorods of 6 nm in diameters and two different aspect ratios (7 and 15). They display optimized magnetic properties, with a spontaneous magnetization just below the bulk one, and large coercive fields (up to 6.5 kOe at 300 K) as a result of coherent switching (i.e., Stoner and Wohlfarth mechanism). We measured a strong effective anisotropy very close to the expected value resulting from the sum of shape and magnetocrystalline contributions.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Magnetic domain wall pinning by a curved conduit

E. R. Lewis, D. Petit, L. Thevenard, A. V. Jausovec, L. O’Brien, D. E. Read, and R. P. Cowburn

Appl. Phys. Lett. 95, 152505 (2009); http://dx.doi.org/10.1063/1.3246154 (3 pages) | Cited 9 times

Online Publication Date: 13 October 2009

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The pinning of a magnetic domain wall in a curved Permalloy (NiFe) nanostrip is experimentally studied. We examine the dependence of the pinning on both the radius of curvature of the bend and the chirality of the transverse domain wall. We find that bends act as potential wells or potential barriers depending on the chirality of the domain wall; the pinning field in both cases increases with decreasing radius of curvature. Micromagnetic simulations are consistent with the experimental results and show that both exchange and demagnetizing energies play an important role.
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75.60.Ch Domain walls and domain structure

Detection of the static and kinetic pinning of domain walls in ferromagnetic nanowires

Sung-Min Ahn, Kyoung-Woong Moon, Dong-Hyun Kim, and Sug-Bong Choe

Appl. Phys. Lett. 95, 152506 (2009); http://dx.doi.org/10.1063/1.3248220 (3 pages) | Cited 15 times

Online Publication Date: 13 October 2009

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Two distinct pinning mechanisms named as kinetic and static pinning of magnetic domain wall (DW) are experimentally resolved. Both the pinning situations are realized at an artificial notch on U-shaped Permalloy nanowires, depending on the initial DW states, moving or pinned. The kinetic depinning field—a critical field for a moving DW to be trapped at a notch—is revealed to be distinguishably smaller than the static depinning field—a critical field to depin a trapped DW at the notch. Based on one-dimensional collective model, the discrepancy is explained by the tilting angle of the moving DW.
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75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys

Tuning exchange bias in Ni/FeF2 heterostructures using antidot arrays

M. Kovylina, M. Erekhinsky, R. Morales, J. E. Villegas, I. K. Schuller, A. Labarta, and X. Batlle

Appl. Phys. Lett. 95, 152507 (2009); http://dx.doi.org/10.1063/1.3248306 (3 pages) | Cited 6 times

Online Publication Date: 14 October 2009

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The transition from positive to negative exchange bias can be systematically tuned with antidot arrays artificially introduced into Ni/FeF2 ferromagnetic/antiferromagnetic heterostructures. These results are a consequence of the energy balance and suggest that the nanostructure plays a key role in the formation of pinned uncompensated spin regions in the antiferromagnetic FeF2 layer. These noninterfacial magnetic moments created at the antidot faces favor the onset of positive exchange bias at lower cooling fields.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions

Anisotropic stress relief mechanism in epitaxial La0.67Sr0.33MnO3 films

Arturas Vailionis, Hans Boschker, Evert Houwman, Gertjan Koster, Guus Rijnders, and Dave H. A. Blank

Appl. Phys. Lett. 95, 152508 (2009); http://dx.doi.org/10.1063/1.3249583 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2009

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We report an anisotropic misfit stress relief mechanism in thin La0.67Sr0.33MnO3 (LSMO) films coherently grown on NdGaO3(110) substrates. These results are uniquely related to the orthorhombicity of the LSMO. The x-ray diffraction measurements and quantitative simulations demonstrate that biaxial mismatch stress is relieved differently along in-plane directions perpendicular to each other: in the [1math0] direction stress is accommodated by decrease of the γ angle of the orthorhombic LSMO unit cell, while in the [001] direction stress is partially relieved by periodic lattice modulations.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

Self-oscillations in a superconducting stripline resonator integrated with a dc superconducting quantum interference device

Eran Segev, Oren Suchoi, Oleg Shtempluck, and Eyal Buks

Appl. Phys. Lett. 95, 152509 (2009); http://dx.doi.org/10.1063/1.3250167 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2009

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We study self-sustained oscillations in a Nb superconducting stripline resonator integrated with a dc superconducting quantum interference device (SQUID). We find that both the power threshold where these oscillations start and the oscillation frequency are periodic in the applied magnetic flux threading the SQUID loop. A theoretical model which attributes the self-sustained oscillations to a thermal instability in the dc-SQUID yields a good agreement with the experimental results. This flux dependant nonlinearity may be used for quantum state reading of a qubit-superconducting resonator integrated device.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Nanowires formation and the origin of ferromagnetism in a diluted magnetic oxide

F. Vidal, Y. Zheng, J. Milano, D. Demaille, P. Schio, E. Fonda, and B. Vodungbo

Appl. Phys. Lett. 95, 152510 (2009); http://dx.doi.org/10.1063/1.3250173 (3 pages) | Cited 8 times

Online Publication Date: 14 October 2009

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The ferromagnetic response from Co-doped CeO2 epilayers is shown to be linked to the formation of Co metallic nanowires (diameters in the 3–7 nm range) within the oxide matrix. These results (i) illustrate the key role of the shape anisotropy of metallic inclusions in diluted magnetic oxides (DMO), (ii) stress the importance to monitor the out-of-plane response of DMO, and (iii) suggest that some dilute systems previously thought to be intrinsic ferromagnet may be reexamined.
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75.70.Ak Magnetic properties of monolayers and thin films
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.55.-a Thin film structure and morphology
75.50.Cc Other ferromagnetic metals and alloys
75.50.Dd Nonmetallic ferromagnetic materials
75.75.-c Magnetic properties of nanostructures

Magnetic force microscopy investigation of the static magnetic domain structure and domain rotation in Fe-x at. %Ga alloys

Feiming Bai, Huaiwu Zhang, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 95, 152511 (2009); http://dx.doi.org/10.1063/1.3238062 (3 pages)

Online Publication Date: 14 October 2009

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Magnetic domain structures and domain rotation process in Fe-x at. %Ga (x = 12, 19, and 25) alloys have been studied by magnetic force microscopy. Our results show that the missing connection between magnetic domains and the underlying microstructure [ Xing and Lograsso, Appl. Phys. Lett. 93, 182501 (2008) ] is (i) a perpendicular magnetic anisotropy; and (ii) domain irregularities/fluctuations induced by a quenched random-field condition: both of which may have direct relations with dispersed low-symmetry nanoprecipitates [ Cao, et al., Phys. Rev. Lett. 102, 127201 (2009) ].
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75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction

Magnetoresistance effect in antiferromagnet/nonmagnet/antiferromagnet multilayers

L. Wang, S. G. Wang, Syed Rizwan, Q. H. Qin, and X. F. Han

Appl. Phys. Lett. 95, 152512 (2009); http://dx.doi.org/10.1063/1.3248223 (3 pages) | Cited 3 times

Online Publication Date: 14 October 2009

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The magnetoresistance (MR) effect between two antiferromagnetic layers separated by a nonmagnetic Cu layer was investigated. The MR ratio of 0.5% was observed in the structure of IrMn(8)/Cu(2.8)/IrMn(0.5)/CoFe(8) (in nanometers), where IrMn stands for Ir22Mn78 and CoFe for Co90Fe10. The study of different structures with and without top IrMn layer indicates that the MR effect originates from the giant magnetoresistance effect between the uncompensated magnetic moments at the IrMn interfaces across nonmagnetic Cu spacer.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ee Antiferromagnetics

Characterization of tips for spin-polarized scanning tunneling microscopy

G. Rodary, S. Wedekind, H. Oka, D. Sander, and J. Kirschner

Appl. Phys. Lett. 95, 152513 (2009); http://dx.doi.org/10.1063/1.3246150 (3 pages) | Cited 8 times

Online Publication Date: 15 October 2009

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We propose a conclusive characterization of the magnetic configuration of tips for spin-polarized scanning tunneling microscopy studies. We show that both careful tip preparation and characterization by tunneling spectroscopy need to be augmented by in-field measurements to ensure a reliable analysis of a magnetic contrast in spin-polarized scanning tunneling microscopy studies.
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07.79.Cz Scanning tunneling microscopes
75.30.Ds Spin waves
72.25.-b Spin polarized transport

Shaping the response pulse of superconducting nanowire single photon detection with a snubber

L. X. You and X. F. Shen

Appl. Phys. Lett. 95, 152514 (2009); http://dx.doi.org/10.1063/1.3250169 (3 pages)

Online Publication Date: 15 October 2009

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Unavoidable kinetic inductance of the superconducting nanowire single photon detector results in the signal pulse with a slow falling edge and a large pulse width. It has been a limit for improving the repetition rate for single photon detection. With a snubber made of a coaxial cable terminated with a resistive pot, the original signal pulse can be shaped. A sharp falling edge can be produced with suitable snubber parameters and the final output pulse has a symmetric wave. The pulse width (full width at half maximum) is reduced from 5 to 1 ns.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Simultaneous in-plane and out-of-plane exchange bias using a single antiferromagnetic layer resolved by x-ray magnetic circular dichroism

J. Nogués, S. Stepanow, A. Bollero, J. Sort, B. Dieny, F. Nolting, and P. Gambardella

Appl. Phys. Lett. 95, 152515 (2009); http://dx.doi.org/10.1063/1.3232213 (3 pages) | Cited 6 times

Online Publication Date: 15 October 2009

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We present a study of exchange bias in ferromagnet/antiferromagnet/ferromagnet (FM/AFM/FM) trilayers, with in-plane and out-plane easy axes. Using element-specific x-ray magnetic circular dichroism, we demonstrate that simultaneous in-plane and out-of-plane exchange bias can be induced using a single antiferromagnet and zero field cooling, whereas field cooling only induces exchange bias to the layer with easy axis parallel to the cooling field. Our results further evidence the presence of pinned uncompensated moments in both the FM and AFM layers, implying that the AFM layer is capable of supporting uncompensated spins in two orthogonal directions at the same time.
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78.20.Ls Magneto-optical effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys

Development of high critical current density in multifilamentary round-wire Bi2Sr2CaCu2O8+δ by strong overdoping

T. Shen, J. Jiang, A. Yamamoto, U. P. Trociewitz, J. Schwartz, E. E. Hellstrom, and D. C. Larbalestier

Appl. Phys. Lett. 95, 152516 (2009); http://dx.doi.org/10.1063/1.3242339 (3 pages) | Cited 13 times

Online Publication Date: 16 October 2009

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Bi2Sr2CaCu2O8+δ is the only cuprate superconductor that can be made into a round-wire conductor form with a high enough critical current density Jc for applications. Here we show that the Jc(5 T,4.2 K) of such Ag-sheathed filamentary wires can be doubled to more than 1.4×105 A/cm2 by low temperature oxygenation. Careful analysis shows that the improved performance is associated with a 12 K reduction in transition temperature Tc to 80 K, an increase in flux pinning, and particularly a significant enhancement in intergranular connectivity. In spite of the macroscopically untextured nature of the wire, overdoping is highly effective in producing high Jc values.
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74.25.Sv Critical currents
74.62.Yb Other effects
61.72.up Other materials
74.72.-h Cuprate superconductors
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