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11 Feb 2013

Volume 102, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 063701 (2013); http://dx.doi.org/10.1063/1.4790115 (5 pages)

In-Tsang Lin, Hong-Chang Yang, and Jyh-Horng Chen
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Improvement of heat transfer efficiency at solid-gas interfaces by self-assembled monolayers

Zhi Liang, William Evans, Tapan Desai, and Pawel Keblinski

Appl. Phys. Lett. 102, 061907 (2013); http://dx.doi.org/10.1063/1.4792530 (5 pages) | Cited 1 time

Online Publication Date: 13 February 2013

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Using molecular dynamics simulations, we demonstrate that the efficiency of heat exchange between a solid and a gas can be maximized by functionalizing solid surface with organic self-assembled monolayers (SAMs). We observe that for bare metal surfaces, the thermal accommodation coefficient (TAC) strongly depends on the solid-gas interaction strength. For metal surfaces modified with organic SAMs, the TAC is close to its theoretical maximum and is essentially independent from the SAM-gas interaction strength. The analysis of the simulation results indicates that softer and lighter SAMs, compared to the bare metal surfaces, are responsible for the greatly enhanced TAC.
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44.35.+c Heat flow in multiphase systems
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Sn and Nb modified ultrafine Ti-based bulk alloys with high-strength and enhanced ductility

G. H. Cao, R. Schneider, D. Gerthsen, R. Chulist, R. Schaarschuch, C.-G. Oertel, and W. Skrotzki

Appl. Phys. Lett. 102, 061908 (2013); http://dx.doi.org/10.1063/1.4792592 (4 pages)

Online Publication Date: 13 February 2013

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Sn and Nb modified ultrafine eutectic Ti−Fe alloys with high strength and plasticity prepared by cold crucible levitation melting were tested in compression at room temperature. (Ti70.5Fe29.5)93.15Sn3.85Nb3 alloy exhibited an ultimate compressive strength of 2.36 GPa at 15% plastic strain. Electron microscopy revealed that lamellar structures in Ti70.5Fe29.5 alloy could be tailored by the addition of Sn and Nb to obtain a globular structure. The microstructural refinement, morphology of phase constituents, and their relationships to the mechanical properties are discussed.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
64.70.dj Melting of specific substances

Iso-structural phase transition in YMnO3 nanosized particles

Saurabh Tripathi and Valeri Petkov

Appl. Phys. Lett. 102, 061909 (2013); http://dx.doi.org/10.1063/1.4791596 (4 pages)

Online Publication Date: 13 February 2013

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Structure studies on multiferroic YMnO3 particles with size varying between 467 ± 42 nm (bulk) and 28 ± 3 nm was carried out using high-energy synchrotron x-ray diffraction. Analysis of the diffraction data reveals that when the particles size decreases to about 121 nm an iso-structural phase transition takes place. The transition is accompanied by a substantial change in the unit cell volume and the ratio (c/a) of the parameters of the hexagonal lattice of YMnO3. The phase transition is similar to the one reported in bulk YMnO3 heated to temperatures of about 920 K. In this letter, we argue that the phase transition in nanosized YMnO3 is of an order-disorder type.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
75.85.+t Magnetoelectric effects, multiferroics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.60.Cn Order-disorder transformations
64.70.Nd Structural transitions in nanoscale materials

Resonant Raman scattering from CdS nanocrystals enhanced by interstitial Mn

P. Q. Zhao, L. Z. Liu, H. T. Xue, X. L. Wu, J. C. Shen, and Paul K. Chu

Appl. Phys. Lett. 102, 061910 (2013); http://dx.doi.org/10.1063/1.4792512 (4 pages)

Online Publication Date: 14 February 2013

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Different Raman scattering effects are observed from CdS and Mn-doped CdS nanocrystals (NCs) with an average size of 5.1 nm synthesized by the reverse-micelle method. The intensity of the longitudinal optical (LO) phonon spectrum acquired from the Mn-doped CdS NCs is more than 20 times larger than that from the undoped CdS NCs. Spectroscopic and theoretical analyses reveal that the enhancement is caused by the interstitial Mn dopants, which decrease the NC surface deformation potential due to the small dielectric constant of the metal resulting in enhanced coupling between the LO phonon and surface plasmon.
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78.30.Fs III-V and II-VI semiconductors
63.20.kk Phonon interactions with other quasiparticles
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
77.22.Ch Permittivity (dielectric function)

Vortical structures of supersonic flow over a delta-wing on a flat plate

D. P. Wang, Z. X. Xia, Y. X. Zhao, Q. H. Wang, and B. Liu

Appl. Phys. Lett. 102, 061911 (2013); http://dx.doi.org/10.1063/1.4790286 (4 pages)

Online Publication Date: 14 February 2013

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Employing the nanoparticle-based planar laser scattering (NPLS), supersonic flow over a delta-winged vortex generator on a flat plate was experimentally investigated in a supersonic quiet wind tunnel at Ma = 2.68. The fine structures of the flow field, shock waves, separation vortices, wake, and boundary layer transition were observed in the NPLS images. According to the time-correlation of the NPLS images and the measurement results of particle image velocimetry, the structural model of the flow field was improved further, and coherent wake structures were observed, which is of significance theoretically and in engineering application.
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47.32.Ff Separated flows
47.40.Ki Supersonic and hypersonic flows
47.40.Nm Shock wave interactions and shock effects
47.80.Jk Flow visualization and imaging
47.85.Np Fluidics

Quantitative scanning thermal microscopy of ErAs/GaAs superlattice structures grown by molecular beam epitaxy

K. W. Park, H. P. Nair, A. M. Crook, S. R. Bank, and E. T. Yu

Appl. Phys. Lett. 102, 061912 (2013); http://dx.doi.org/10.1063/1.4792757 (5 pages)

Online Publication Date: 15 February 2013

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A proximal probe-based quantitative measurement of thermal conductivity with ∼100–150 nm lateral and vertical spatial resolution has been implemented. Measurements on an ErAs/GaAs superlattice structure grown by molecular beam epitaxy with 3% volumetric ErAs content yielded thermal conductivity at room temperature of 9 ± 2 W/m K, approximately five times lower than that for GaAs. Numerical modeling of phonon scattering by ErAs nanoparticles yielded thermal conductivities in reasonable agreement with those measured experimentally and provides insight into the potential influence of nanoparticle shape on phonon scattering. Measurements of wedge-shaped samples created by focused ion beam milling provide direct confirmation of depth resolution achieved.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
66.70.Df Metals, alloys, and semiconductors
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Lanthanide impurities in wide bandgap semiconductors: A possible roadmap for spintronic devices

G. Caroena, W. V. M. Machado, J. F. Justo, and L. V. C. Assali

Appl. Phys. Lett. 102, 062101 (2013); http://dx.doi.org/10.1063/1.4791787 (4 pages)

Online Publication Date: 11 February 2013

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The electronic properties of lanthanide (from Eu to Tm) impurities in wurtzite gallium nitride and zinc oxide were investigated by first principles calculations, using an all electron methodology plus a Hubbard potential correction. The results indicated that the 4f-related energy levels remain outside the bandgap in both materials, in good agreement with a recent phenomenological model, based on experimental data. Additionally, zinc oxide doped with lanthanide impurities became an n-type material, showing a coupling between the 4f-related spin polarized states and the carriers. This coupling may generate spin polarized currents, which could lead to applications in spintronic devices.
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61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
72.25.Dc Spin polarized transport in semiconductors
72.80.Ey III-V and II-VI semiconductors

Gamma irradiation impact on electronic carrier transport in AlGaN/GaN high electron mobility transistors

C. Schwarz, A. Yadav, M. Shatkhin, E. Flitsiyan, L. Chernyak, V. Kasiyan, L. Liu, Y. Y. Xi, F. Ren, S. J. Pearton, C. F. Lo, J. W. Johnson, and E. Danilova

Appl. Phys. Lett. 102, 062102 (2013); http://dx.doi.org/10.1063/1.4792240 (3 pages) | Cited 1 time

Online Publication Date: 11 February 2013

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AlGaN/GaN high electron mobility transistors were irradiated with 60Co gamma-rays to doses up to 1000 Gy, in order to analyze the effects of irradiation on the devices' transport properties. Temperature-dependent electron beam-induced current measurements, conducted on the devices before and after exposure to gamma-irradiation, allowed for the obtaining of activation energies related to radiation-induced defects due to nitrogen vacancies. DC current-voltage measurements were also conducted on the transistors to assess the impact of gamma-irradiation on transfer, gate, and drain characteristics.
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85.30.Tv Field effect devices

High performance InGaZnO thin film transistor with InGaZnO source and drain electrodes

Hung-Chi Wu and Chao-Hsin Chien

Appl. Phys. Lett. 102, 062103 (2013); http://dx.doi.org/10.1063/1.4789997 (4 pages)

Online Publication Date: 11 February 2013

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This work demonstrates In-Ga-Zn-O (IGZO) as source and drain electrodes in IGZO-thin film transistors (TFTs). The fabricated TFT depicts excellent electrical properties; its mobility is 18.02 (cm2/V s), threshold voltage (Vth) is 0.3 (V), on/off ratio is 1.63 × 108 and subthreshold swing (S.S.) is 239 (mV/decade). We find using rapid thermal annealing treatment can convert IGZO into an effective conductor, and the transparency of IGZO remained almost unchanged. We also find sufficient thermal budget is needed for getting stable transfer curve and output characteristic; otherwise, current fluctuation in on-state can be easily observed. With IGZO electrodes, fully transparent IGZO-TFTs can be thus realized on a glass substrate.
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85.30.Tv Field effect devices
82.45.Fk Electrodes

Rapid hot-electron energy relaxation in lattice-matched InAlN/AlN/GaN heterostructures

J.-Z. Zhang, A. Dyson, and B. K. Ridley

Appl. Phys. Lett. 102, 062104 (2013); http://dx.doi.org/10.1063/1.4792276 (4 pages)

Online Publication Date: 12 February 2013

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Hot-electron energy relaxation is theoretically studied for a typical lattice-matched InAlN/AlN/GaN heterostructure, including effects of non-equilibrium phonons and screening from the mobile electrons in the GaN channel. A dramatic fall of relaxation time occurs at low electron temperatures (<500 K) due to the exponentially increased phonon generation as well as fast decreased screening and hot-phonon effect. At high electron temperatures (>1500 K), on the other hand, the hot-phonon effect is very weak because of short optical phonon lifetimes (experimental value ∼0.1 ps), and the electron relaxation is dictated by the screened electron-phonon interactions which alone yield a nearly constant relaxation time ∼0.1 ps. With increasingly fast optical-phonon decay, therefore the high-temperature electron relaxation time decreases slowly with the electron temperature, with its limiting value set entirely by the screened electron-phonon interactions alone. The calculated dependence of the relaxation time on the electron temperature and the high-temperature relaxation times ∼0.1 ps are in good agreement with experimental results.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
63.20.kd Phonon-electron interactions
71.38.-k Polarons and electron-phonon interactions
72.20.Fr Low-field transport and mobility; piezoresistance

Pressure-induced phase transformation of In2Se3

Anya M. Rasmussen, Samuel T. Teklemichael, Elham Mafi, Yi Gu, and Matthew D. McCluskey

Appl. Phys. Lett. 102, 062105 (2013); http://dx.doi.org/10.1063/1.4792313 (4 pages)

Online Publication Date: 13 February 2013

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In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Using x-ray diffraction and a diamond-anvil cell, the pressure-dependent structural properties of In2Se3 powder were studied at room temperature. α-In2Se3 transforms into the β phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The β phase persists upon decompression to ambient pressure. Raman spectroscopy experiments confirm this result. The bulk moduli are reported and the c/a ratio for the β phase is shown to have a highly nonlinear dependence on pressure.
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64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics
81.30.Dz Phase diagrams of other materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.50.-p High-pressure effects in solids and liquids

Band alignment between Ta2O5 and metals for resistive random access memory electrodes engineering

V. Y.-Q. Zhuo, Y. Jiang, M. H. Li, E. K. Chua, Z. Zhang, J. S. Pan, R. Zhao, L. P. Shi, T. C. Chong, and J. Robertson

Appl. Phys. Lett. 102, 062106 (2013); http://dx.doi.org/10.1063/1.4792274 (5 pages)

Online Publication Date: 13 February 2013

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Band alignment of resistive random access memory (RRAM) switching material Ta2O5 and different metal electrode materials was examined using high-resolution X-ray photoelectron spectroscopy. Schottky and hole barrier heights at the interface between electrode and Ta2O5 were obtained, where the electrodes consist of materials with low to high work function (Φm,vac from 4.06 to 5.93 eV). Effective metal work functions were extracted to study the Fermi level pinning effect and to discuss the dominant conduction mechanism. An accurate band alignment between electrodes and Ta2O5 is obtained and can be used for RRAM electrode engineering and conduction mechanism study.
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84.30.Sk Pulse and digital circuits

Visible single-photon emission from a nitrogen impurity center in AlAs

M. Jo, T. Mano, T. Kuroda, Y. Sakuma, and K. Sakoda

Appl. Phys. Lett. 102, 062107 (2013); http://dx.doi.org/10.1063/1.4792315 (3 pages)

Online Publication Date: 14 February 2013

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We report visible single-photon emission from a nitrogen impurity center in AlAs grown on GaAs(001). Sharp emission lines are observed at 2.1–2.2 eV, below the X-conduction bandedge of AlAs from N δ-doped AlAs. The quadratic increase in the photoluminescence intensity with the N concentration reveals that the nitrogen impurity centers consist of NN pairs. Polarization analysis reveals that the peak at 2.191 eV consists of different pair configurations, while the peak at 2.165 eV contains only a single pair configuration along the 〈110〉 direction. Photon correlation measurement gives the second-order correlation function g(2)(0) = 0.33, demonstrating single-photon statistics in emissions from an NN pair.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
61.72.jn Color centers
61.72.uj III-V and II-VI semiconductors
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Polarization induced hole doping in graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy

Shibin Li, Ting Zhang, Jiang Wu, Yajie Yang, Zhiming Wang, Zhiming Wu, Zhi Chen, and Yadong Jiang

Appl. Phys. Lett. 102, 062108 (2013); http://dx.doi.org/10.1063/1.4792685 (3 pages)

Online Publication Date: 14 February 2013

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Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy. Graded AlxGa1−xN and conventional Al0.7Ga0.3N layers grown on AlN are beryllium (Be) doped via epitaxial growth. The hole concentration in graded AlxGa1−xN:Be (x = 0.7 ∼ 1) layers demonstrates that polarization generates hole charges from Be dopant. The Al0.7Ga0.3N layer is not conductive owing to the absence of carriers generated from the Be dopant without the inducement of polarization. Polarization doping provides an approach to high efficiency p-type doping in high Al composition AlGaN.
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68.55.ag Semiconductors
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Cu3BiS3 as a potential photovoltaic absorber with high optical efficiency

Mukesh Kumar and Clas Persson

Appl. Phys. Lett. 102, 062109 (2013); http://dx.doi.org/10.1063/1.4792751 (4 pages) | Cited 2 times

Online Publication Date: 15 February 2013

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Cu3BiS3 is a potential photovoltaic material. Employing a first-principles approach, we calculate the structural, electronic, and optical properties of Cu3BiS3, and we demonstrate that Cu3BiS3 is an indirect band gap semiconductor in contrast to similar chalcogenide semiconductors. The fundamental band gap energy is estimated to be Eg ≈ 1.5–1.7 eV. The analysis reveals that Cu3BiS3 has a much stronger absorption coefficient (>105 cm−1) compared to other Cu-S based materials like CuInS2 and Cu2ZnSnS4. This is explained by the presence of localized Bi 6p states in the band gap region, generating a flat lowest conduction band.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Green to blue polarization compensated c-axis oriented multi-quantum wells by AlGaInN barrier layers

A. Dadgar, L. Groh, S. Metzner, S. Neugebauer, J. Bläsing, T. Hempel, F. Bertram, J. Christen, A. Krost, Z. Andreev, and B. Witzigmann

Appl. Phys. Lett. 102, 062110 (2013); http://dx.doi.org/10.1063/1.4793185 (4 pages)

Online Publication Date: 15 February 2013

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We report on an over 50% reduction in polarization field strength in c-axis oriented InGaN multi-quantum wells (MQW) by applying quaternary AlGaInN barrier layers with better polarization matching to InGaN than GaN barriers. With the reduction in polarization fields, a strong blue-shift in photoluminescence is observed in agreement with theoretical expectation and simulations. By gracing incidence x-ray diffraction measurements, we demonstrate that partial relaxation already occurs for GaN/InGaN MQWs. As a consequence, the requirement of higher In-content layers for green light emission is in conflict with increasing strain leading to lattice relaxation.
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78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
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Reversal process of a magnetic vortex core under the combined action of a perpendicular field and spin transfer torque

N. Locatelli, A. E. Ekomasov, A. V. Khvalkovskiy, Sh. A. Azamatov, K. A. Zvezdin, J. Grollier, E. G. Ekomasov, and V. Cros

Appl. Phys. Lett. 102, 062401 (2013); http://dx.doi.org/10.1063/1.4790841 (5 pages)

Online Publication Date: 11 February 2013

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In a nanopillar with dipolarly coupled vortices, we present an experimental and simulation study to understand how the interplay between the bias field and spin transfer torque impacts reversal of the vortex cores. We find that, depending on the current values, vortex cores might experience different physical mechanisms for their reversal, namely, a static or a dynamic switching. We believe that our results might be useful in the context of vortex based non volatile memories, as a current controlled selective core switching is proposed.
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75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ferromagnetic resonance study of dual exchange bias field behavior in NiFe/IrMn/Co trilayers

M. Tafur, M. A. Sousa, F. Pelegrini, V. P. Nascimento, and E. Baggio-Saitovitch

Appl. Phys. Lett. 102, 062402 (2013); http://dx.doi.org/10.1063/1.4791574 (5 pages) | Cited 1 time

Online Publication Date: 11 February 2013

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Magnetometry study of magnetron sputtered NiFe/IrMn/Co trilayers reveal that the exchange bias field at the NiFe/IrMn interface decreases with increasing NiFe layer thickness, up to 150 Å. At the IrMn/Co interface, a decrease also occurs when the NiFe layer thickness increases. Ferromagnetic resonance measurements at X and Q-band frequencies reveal that the same dependence at both interfaces, up to a 70 Å thick NiFe, is due to a spiraling interlayer coupling between the NiFe and Co layers. Unexpected increase with thicker NiFe layer is due to domain walls at the NiFe/IrMn interface in the presence of low static magnetic fields.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Cd Deposition by sputtering
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Structure of epitaxial L10-FePt/MgO perpendicular magnetic tunnel junctions

Amit Kohn, Nadav Tal, Ayala Elkayam, Andras Kovàcs, Dalai Li, Shouguo Wang, Saman Ghannadzadeh, Thorsten Hesjedal, and Roger C. C. Ward

Appl. Phys. Lett. 102, 062403 (2013); http://dx.doi.org/10.1063/1.4791576 (5 pages)

Online Publication Date: 11 February 2013

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Perpendicular magnetic tunnel junctions (p-MTJs) with MgO barriers are interesting for high-density information-storage devices. Chemically ordered L10-FePt is a potential electrode due to its large perpendicular magnetocrystalline anisotropy. To-date, a single theoretical study on L10-FePt/MgO p-MTJ based on an idealized structure reported significant dependence of spin-dependent tunneling on interface structure. [Y. Taniguchi et al., IEEE Trans. Magn. 44, 2585 (2008).] We report a structural study of epitaxial L10-FePt(001)[110]//MgO(001)[110]//L10-FePt(001)[110] p-MTJs, focusing on the interfaces using aberration-corrected scanning transmission electron microscopy. Interfaces are semi-coherent, with oxygen atomic-columns of MgO located opposite to iron atomic-columns in L10-FePt. Up to three lattice planes show atomic-column steps, the origin of which is attributed to antiphase boundaries in L10-FePt.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness
75.30.Gw Magnetic anisotropy

Effect of film thickness and biaxial strain on the curie temperature of EuO

A. Melville, T. Mairoser, A. Schmehl, T. Birol, T. Heeg, B. Holländer, J. Schubert, C. J. Fennie, and D. G. Schlom

Appl. Phys. Lett. 102, 062404 (2013); http://dx.doi.org/10.1063/1.4789972 (5 pages)

Online Publication Date: 11 February 2013

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The effects of film thickness and epitaxial strain on the magnetic properties of commensurate EuO thin films grown on single crystalline (001) yttria-stabilized zirconia (YSZ) and (110) LuAlO3 substrates are presented. Magnetic measurements show a reduction in the Curie temperature (TC) for EuO/YSZ films thinner than ∼10 nm. Additionally, the EuO/LuAlO3 films exhibit a systematically lower TC than the corresponding EuO/YSZ films. This further reduction in TC is attributed to the effect of biaxial tensile strain arising from lattice mismatch: 0.0% for EuO/YSZ and +1.0% for EuO/LuAlO3.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.55.aj Insulators

High resolution switching magnetization magnetic force microscopy

V. Cambel, M. Precner, J. Fedor, J. Šoltýs, J. Tóbik, T. Ščepka, and G. Karapetrov

Appl. Phys. Lett. 102, 062405 (2013); http://dx.doi.org/10.1063/1.4791591 (4 pages)

Online Publication Date: 12 February 2013

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We introduce switching magnetization magnetic force microscopy based on two-pass scanning atomic force microscopy with reversed tip magnetization between the scans. Within this approach the sum of the scanned data with reversed tip magnetization depicts local van der Waals forces, while their differences map the local magnetic forces. Here we implement this method by fabricating low-momentum magnetic probes that exhibit magnetic single domain state, which can be easily reversed in low external field during the scanning. Measurements on high-density parallel and perpendicular magnetic recording media show enhanced spatial resolution of magnetization.
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07.79.Pk Magnetic force microscopes
75.50.Ss Magnetic recording materials
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
07.79.Lh Atomic force microscopes

Anomalous magnetoresistance and magnetocaloric properties of NdRu2Ge2

Bibekananda Maji, K. G. Suresh, and A. K. Nigam

Appl. Phys. Lett. 102, 062406 (2013); http://dx.doi.org/10.1063/1.4791674 (5 pages)

Online Publication Date: 12 February 2013

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It is found that the polycrystalline NdRu2Ge2 undergoes two successive magnetic transitions at Tt = 10 K and TN = 19 K. Evidence of metamagnetic transition is detected in the magnetization isotherm data in the antiferromagnetic regime. Temperature dependence of magnetoresistance (MR) shows that the relative magnitudes of MR at TN and Tt change considerably as the field is increased from 10 kOe to 30 kOe. Moreover, the MR is found to be positive below 9 K for 30 kOe field although the material is ferromagnetic at these temperatures. The highest value of negative MR near TN is about 42% in a field of 30 kOe, while the positive MR is about 35% at 3 K in a field of 50 kOe. Like MR, the magnetocaloric effect (MCE) at TN and Tt also shows anomalous behavior. The relative magnitudes of MCE at these temperatures are found to change with increase in field. It appears that the high field (>10 kOe) magnetic state below TN is complex, giving rise to some antiferromagnetic-like fluctuations, affecting the MR and MCE behavior.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Role of covalent hybridization in the martensitic structure and magnetic properties of shape-memory alloys: The case of Ni50Mn5+xGa35-xCu10

G. J. Li, E. K. Liu, H. G. Zhang, Y. J. Zhang, G. Z. Xu, H. Z. Luo, H. W. Zhang, W. H. Wang, and G. H. Wu

Appl. Phys. Lett. 102, 062407 (2013); http://dx.doi.org/10.1063/1.4791701 (4 pages) | Cited 1 time

Online Publication Date: 12 February 2013

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The influence of covalent hybridization on the martensitic structure and magnetic properties of Ni50Mn5+xGa35−xCu10 shape-memory alloys has been investigated. It is found that the lattice distortion (c − a)/a of L10 martensite linearly increases upon substitution of Mn for Ga, showing a change of slope at Ga = 25 at. %, which is ascribed to a weakened covalent hybridization between main-group and transition-metal atoms. Moreover, due to the competition between the covalent hybridization and the magnetic ordering of the substituted Mn atoms, the magnetic moment per formula unit and the Curie temperature show maxima at Ga = 25 at. % as well. This behavior is closely associated with the corresponding changes of the strength of the covalent hybridization. The results, therefore, suggest that a careful control of the concentration of main-group atoms in Heusler alloys may serve as a tuning parameter for finding multifunctional materials.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Dk Alloys

Optical manipulation of electron spin coherence in colloidal CdS quantum dots

D. H. Feng, L. F. Shan, T. Q. Jia, X. Q. Pan, H. F. Tong, L. Deng, Z. R. Sun, and Z. Z. Xu

Appl. Phys. Lett. 102, 062408 (2013); http://dx.doi.org/10.1063/1.4791790 (4 pages)

Online Publication Date: 12 February 2013

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We report experimental studies of optical manipulation of electron spin coherence by linearly or circularly polarized short laser pulses at room temperature, in an ensemble of colloidal CdS quantum dots. In addition to a conventional pump-probe configuration, a linearly polarized prepump pulse before the pump could significantly enhance the amplitude of pump-induced electron spin coherence, owing to the fact that prepump pulses produce more resident electrons. And a linearly or circularly polarized control pulse after the pump will efficiently suppress the spin coherence, because of the re-excitation of spin-polarized electrons to trion states by the absorption of control photons.
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78.47.D- Time resolved spectroscopy (>1 psec)
71.35.Pq Charged excitons (trions)
72.25.Dc Spin polarized transport in semiconductors
78.67.Hc Quantum dots
82.70.Dd Colloids

Probing nanowire edge roughness using an extended magnetic domain wall

K. J. O'Shea, J. Tracey, S. Bramsiepe, and R. L. Stamps

Appl. Phys. Lett. 102, 062409 (2013); http://dx.doi.org/10.1063/1.4792314 (4 pages) | Cited 1 time

Online Publication Date: 13 February 2013

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Using Lorentz transmission electron microscopy, a unique experiment is realised in which an extended magnetic domain wall in a ferromagnetic nanowire, strongly pinned at one end, is utilised as a local probe of the distribution of pinning sites along the nanowire edges. Fresnel imaging is used to examine the detailed de-pinning process and extract a distribution of pinning energies along the wire. The pinning sites were found to be randomly distributed with surprisingly little correlation between pinning site location and visible structural features along the wire edge.
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75.75.-c Magnetic properties of nanostructures
75.60.Ch Domain walls and domain structure
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)
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