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10 Mar 2008

Volume 92, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages)

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu
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Structure and magnetic properties of the self-assembled Co52Pt48 nanowire arrays

Jian-Hua Gao, Da-Li Sun, Xiang-Qun Zhang, Qing-Feng Zhan, Wei He, Young Sun, and Zhao-Hua Cheng

Appl. Phys. Lett. 92, 102501 (2008); http://dx.doi.org/10.1063/1.2894199 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2008

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Co52Pt48 nanowire arrays with diameter of about 10 nm have been fabricated by electrodeposition into the anodic aluminum oxide templates. The as-deposited nanowire arrays exhibit fcc structure with [110]-preferred texture along the wire axes. The nanowire arrays present both large magnetocrystalline anisotropy along the [111] direction and strong shape anisotropy along the wire axis, resulting in high coercive fields parallel and perpendicular to the wire axes, respectively. From experimental results and micromagnetic simulation, the coercive field variation as a function of the angles evidenced that the [111] magnetocrystalline anisotropy plays important role besides shape magnetic anisotropy.
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68.65.La Quantum wires (patterned in quantum wells)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
81.15.Pq Electrodeposition, electroplating
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.07.Bc Nanocrystalline materials

Observation of large h/2e and h/4e oscillations in a proximity dc superconducting quantum interference device

J. Wei, P. Cadden-Zimansky, and V. Chandrasekhar

Appl. Phys. Lett. 92, 102502 (2008); http://dx.doi.org/10.1063/1.2894515 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2008

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We have measured the magnetoresistance of a dc superconducting quantum interference device in the form of an interrupted mesoscopic normal metal loop in contact with two superconducting electrodes. Below the transition temperature of the superconducting electrodes, large h/2e periodic magnetoresistance oscillations are observed. By adding a small dc bias to the ac measurement current, h/4e oscillations can be produced. Lowering the temperature further leads to even larger oscillations, and eventually to sharp switching from the superconducting state to the normal state. This flux-dependent resistance could be utilized to make a highly sensitive flux detector.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Boron’s effect on martensitic transformation and magnetocaloric effect in Ni43Mn46Sn11Bx alloys

H. C. Xuan, D. H. Wang, C. L. Zhang, Z. D. Han, B. X. Gu, and Y. W. Du

Appl. Phys. Lett. 92, 102503 (2008); http://dx.doi.org/10.1063/1.2895645 (3 pages) | Cited 12 times

Online Publication Date: 10 March 2008

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The most used method for changing the martensitic transformation temperatures in the ferromagnetic shape memory alloys is tuning the valence election concentration e/a. In this paper, we report an alternative way, i.e., introducing few interstitial boron atoms in Ni43Mn46Sn11 alloy. The experimental results show that the martensitic transformation temperatures increase with the increasing boron content remarkably and large magnetic entropy changes can be obtained in these alloys. A possible origin of the enhanced martensitic transformation temperatures and large magnetic entropy changes is discussed in this paper.
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75.30.Sg Magnetocaloric effect, magnetic cooling
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
61.72.jj Interstitials
75.50.Cc Other ferromagnetic metals and alloys

Structure-magnetic property correlations in the epitaxial FePt system

G. R. Trichy, D. Chakraborti, J. Narayan, and J. T. Prater

Appl. Phys. Lett. 92, 102504 (2008); http://dx.doi.org/10.1063/1.2883933 (3 pages) | Cited 21 times

Online Publication Date: 10 March 2008

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We present findings on the effect of microstructure on magnetic properties of the epitaxial FePt system. Epitaxial c-axis oriented FePt was synthesized on Si (100) using TiN as a template buffer. The microstructure was progressively varied from a 9 nm nanoparticle system to a 30 nm thick continuous thin film. We found that individual nanoparticles showed higher coercivity than the continuous thin film. Within the nanoparticle regime, coercivity increased with increasing particle size. The highest coercivity of 13 500 Oe was realized for a beadlike microstructure, when the individual nanoparticles just begin to merge to form a continuous thin film.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Nanoscale perpendicular magnetic island arrays fabricated by extreme ultraviolet interference lithography

F. Luo, L. J. Heyderman, H. H. Solak, T. Thomson, and M. E. Best

Appl. Phys. Lett. 92, 102505 (2008); http://dx.doi.org/10.1063/1.2841821 (3 pages) | Cited 9 times

Online Publication Date: 11 March 2008

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Magnetic island arrays with a period of 50 nm and uniform over 20×20 μm2 have been fabricated by depositing Co/Pd multilayer films on prepatterned SiOx pillars produced by extreme ultraviolet interference lithography. Scanning electron microscopy and magnetic force microscopy measurements made on the same islands give a direct, island-by-island comparison of the size and remanent switching field. The results demonstrate that the switching field distribution (SFD) is not primarily due to magnetostatic interactions, and a strong dependence of SFD on size is also not observed, indicating that a distribution of material properties is likely to be responsible for the SFD.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys

Ferromagnetic GaMnAs grown on (110) faced GaAs

Ursula Wurstbauer, Matthias Sperl, Marcello Soda, Daniel Neumaier, Dieter Schuh, Günther Bayreuther, Josef Zweck, and Werner Wegscheider

Appl. Phys. Lett. 92, 102506 (2008); http://dx.doi.org/10.1063/1.2884683 (3 pages) | Cited 5 times

Online Publication Date: 11 March 2008

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Thin Ga0.94Mn0.06As layers have been grown by low temperature molecular beam epitaxy on (110) GaAs substrates and on [110] and [−110] oriented GaAs cleaved edges. The Curie temperatures TC for the as-grown samples ranges from 46 to 80 K. After annealing at low temperatures TC increases up to 115 K. In addition, magnetic anisotropies determined by superconducting quantum interference device magnetometry and magnetotransport measurements are reported.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ey III-V semiconductors

Properties of (Zn,Cr)Te semiconductor deposited at room temperature by magnetron sputtering

W. G. Wang, K. J. Han, K. J. Yee, C. Ni, Q. Wen, H. W. Zhang, Y. Zhang, L. Shah, and John Q. Xiao

Appl. Phys. Lett. 92, 102507 (2008); http://dx.doi.org/10.1063/1.2890087 (3 pages) | Cited 3 times

Online Publication Date: 11 March 2008

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We report the fabrication of (Zn,Cr)Te films at room temperature by magnetron sputtering. Various structural and elemental characterizations revealed there was only a zinc blende phase from the ZnTe host and Cr atoms were distributed uniformly in these films. The magnetization measurement by superconducting quantum interference device magnetometer clearly showed that the samples were ferromagnetic at low temperatures with Curie temperature around 150 K. The magnetic circular dichroism measurements confirmed that the observed ferromagnetism was originated from the interaction of substitutional Cr ions and ZnTe host. Transport measurement revealed typical semiconductor behaviors with the large negative magnetoresistance observed.
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81.15.Cd Deposition by sputtering
81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

Sizable room-temperature magnetoresistance in cobalt based magnetic tunnel junctions with out-of-plane anisotropy

Baptiste Carvello, Clarisse Ducruet, Bernard Rodmacq, Stéphane Auffret, Eric Gautier, Gilles Gaudin, and Bernard Dieny

Appl. Phys. Lett. 92, 102508 (2008); http://dx.doi.org/10.1063/1.2894198 (3 pages) | Cited 23 times

Online Publication Date: 11 March 2008

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Submicron alumina based magnetic tunnel junctions (MTJs) using electrodes with out-of-plane magnetic anisotropy were prepared and characterized. Both electrodes are industry-compatible Co/Pt multilayers. The magnetic properties of the unpatterned samples have been investigated through superconducting quantum interference device (SQUID) magnetometry and extraordinary Hall effect: both electrodes have fully out-of-plane magnetic moments and nonoverlapping coercive fields. Transport measurements on the submicron MTJs showed a magnetoresistance (MR) ratio reaching 8% at room temperature. Nanopillars with diameters of 800, 400, and 200 nm patterned from the same wafer show the expected out-of-plane magnetic properties and similar resistance×area products (RA) and MR ratios. The I(V) characteristics of pillars with diameters of 800 and 400 nm could be accounted for with reasonable barrier heights and widths.
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75.47.Pq Other materials
75.30.Gw Magnetic anisotropy
85.25.Dq Superconducting quantum interference devices (SQUIDs)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Magnetotransport properties of CoFeB and Co/Ru interfaces in the current-perpendicular-to-plane geometry

Chiyui Ahn, Kyung-Ho Shin, and William P. Pratt, Jr.

Appl. Phys. Lett. 92, 102509 (2008); http://dx.doi.org/10.1063/1.2891065 (3 pages) | Cited 4 times

Online Publication Date: 12 March 2008

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We have investigated magnetotransport properties of CoFeB and Co/Ru interfaces by measuring the magnetoresistances of sputtered CoFeB-based exchange-biased spin valves and Co/Ru multilayers on the first antiferromagnetic coupling peak at 4.2 K in the current-perpendicular-to-plane geometry. The spin diffusion length lsf and the spin-scattering asymmetry β of Co40Fe40B20 and Co56Fe24B20 are estimated, and the interface specific resistance 2AR* and the interfacial spin-scattering anisotropy γ of Co/Ru interfaces are constrained.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy

Artificial pinning enhancement by multilayer nanostructures in MgB2/Ni thin films

Ken-ichiro Takahashi, Hitoshi Kitaguchi, and Toshiya Doi

Appl. Phys. Lett. 92, 102510 (2008); http://dx.doi.org/10.1063/1.2896305 (3 pages) | Cited 4 times

Online Publication Date: 12 March 2008

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We prepared MgB2/Ni multilayer films on a polished Si (100) single crystal substrate by the growth of alternating layers of MgB2 (15 nm) and Ni ( ∼ 1 nm) layers. We then compared the magnetic field dependence of the critical current density Jc and the global pinning force Fp between films with and without the multilayer nanostructure. In the multilayer MgB2/Ni film, Jc was higher in fields parallel to the substrate than in perpendicular fields, reflecting the layered nanostructure parallel to the substrate. The Jc-B curve has a plateau in parallel fields ranging between 1–5 T, and Jc exceeds 1 MA/cm2, even at 6 T (at 4.2 K). The results indicate that the multilayer nanostructure is effective to enhance flux-pinning performance in parallel fields.
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74.78.-w Superconducting films and low-dimensional structures
61.46.-w Structure of nanoscale materials
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Resonance magnetoelectric interactions due to bending modes in a nickel-lead zirconate titanate bilayer

D. V. Chashin, Y. K. Fetisov, K. E. Kamentsev, and G. Srinivasan

Appl. Phys. Lett. 92, 102511 (2008); http://dx.doi.org/10.1063/1.2896607 (3 pages) | Cited 27 times

Online Publication Date: 12 March 2008

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Resonance magnetoelectric (ME) effects due to bending oscillations have been investigated in bilayers of Ni and lead zirconate titanate (PZT). For nominal sample dimensions, such oscillations occur at a few kilohertz that are much smaller than radial or thickness acoustic modes and result in ME voltage coefficients of 1 V/cm Oe for tangential magnetization. The mode frequencies can be controlled with proper choice for thicknesses of Ni and PZT. Theoretical estimates of mode frequencies are in very good agreement with the data. The resonator is potentially useful for realizing low-loss ME sensor networks for ac fields as low as 10 μOe.
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75.80.+q Magnetomechanical effects, magnetostriction
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Macroscopic pattern formation preceding martensitic transformation in a ferromagnetic shape memory alloy Ni51Fe22Ga27

Y. Murakami, D. Shindo, R. Kainuma, K. Oikawa, and K. Ishida

Appl. Phys. Lett. 92, 102512 (2008); http://dx.doi.org/10.1063/1.2896645 (3 pages) | Cited 4 times

Online Publication Date: 12 March 2008

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This paper reports a macroscopic pattern formation that occurs before the onset of a martensitic transformation in a ferromagnetic shape memory alloy, Ni51Fe22Ga27. Electron holography studies reveal that the magnetic flux pattern in the parent (cubic) phase changes dramatically with cooling. Interestingly, the flux pattern developed in the parent phase is inherited by the martensitic (monoclinic) phase. Observations of the diffuse electron scattering indicate that the change in the magnetic flux pattern is triggered by a lattice anomaly, which appears to produce a long-range strain field in the parent phase.
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75.50.Bb Fe and its alloys
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
64.70.kd Metals and alloys
62.20.fg Shape-memory effect; yield stress; superelasticity

Specular Andreev reflection and magnetoresistance in graphene-based ferromagnet-superconductor double junctions

Chunxu Bai, Yanling Yang, and Xiangdong Zhang

Appl. Phys. Lett. 92, 102513 (2008); http://dx.doi.org/10.1063/1.2894513 (3 pages) | Cited 12 times

Online Publication Date: 12 March 2008

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Spin-polarized transports of relativistic electrons through graphene-based ferromagnet-superconductor double junctions have been investigated theoretically. In the presence of specular Andreev reflection, some unusual properties are found. The oscillating negative magnetoresistance (MR) is not only observed, but the resonance peak of the MR also appears at a certain bias voltage due to the retroreflection crossing over to the specular Andreev reflection. This means that the MR can be tuned by external bias voltage, which benefits the spin-polarized electron device based on the graphene materials.
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85.25.Am Superconducting device characterization, design, and modeling
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Current-induced persistent magnetization in a relaxorlike manganite

H. Sakai and Y. Tokura

Appl. Phys. Lett. 92, 102514 (2008); http://dx.doi.org/10.1063/1.2897299 (3 pages) | Cited 7 times

Online Publication Date: 14 March 2008

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A single crystal of 7% Fe-doped (La0.7Pr0.3)0.65Ca0.35MnO3 shows up as a typical relaxor ferromagnet, where ferromagnetic metallic (FM) and charge-orbital-ordered insulating clusters coexist with controllable volume fraction by external stimuli. There, the persistent FM state can be produced by an electric-current excitation as the filamentary region, the magnetization in which is increased by ∼ 0.4μB per Mn. A clear distinction from the current heating effect in a magnetic field, which conversely leads to a decrease in FM fraction, enables us to bidirectionally switch both the magnetization and resistance by applying the voltages with different magnitudes.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Lx Magnetic oxides

Fluorination-induced magnetism in boron nitride nanotubes from ab initio calculations

Feng Li, Zhonghua Zhu, Xiangdong Yao, Gaoqing Lu, Mingwen Zhao, Yueyuan Xia, and Ying Chen

Appl. Phys. Lett. 92, 102515 (2008); http://dx.doi.org/10.1063/1.2894507 (3 pages) | Cited 16 times

Online Publication Date: 14 March 2008

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Ab initio calculations were conducted to investigate the electronic structures and magnetic properties of fluorinated boron nitride nanotube (F-BNNT). It was found that the chemisorption of F atoms on the B atoms of BNNT can induce spontaneous magnetization, whereas no magnetism can be produced when the B and N atoms are equally fluorinated. This provides a different approach to tune the magnetic properties of BNNTs as well as a synthetic route toward metal-free magnetic materials.
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73.22.-f Electronic structure of nanoscale materials and related systems
71.15.-m Methods of electronic structure calculations
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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