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17 Oct 2011

Volume 99, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 163301 (2011); http://dx.doi.org/10.1063/1.3651509 (3 pages)

Jonathan E. Allen, Kevin G. Yager, Htay Hlaing, Chang-Yong Nam, Benjamin M. Ocko, and Charles T. Black
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Fragility of iron-based glasses

Jong Hyun Na, Marios D. Demetriou, and William L. Johnson

Appl. Phys. Lett. 99, 161902 (2011); http://dx.doi.org/10.1063/1.3651763 (3 pages) | Cited 5 times

Online Publication Date: 17 October 2011

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The viscosity of various iron-based bulk-glass-forming liquids is measured around the glass transition, and the associated fragility is calculated. Fragility is found to vary broadly between compositions, from a low value of ∼43, which indicates fairly “strong” liquid behavior, to ∼65, well within the region of “fragile” behavior. Despite a strong covalent bonding identified in the structure of this class of metal/metalloid glasses, their liquid fragility can be remarkably high, exceeding even the very fragile palladium and platinum bulk-glass formers. An inverse correlation between glass-forming ability and fragility is identified, suggesting that iron-based glasses are effectively “kinetically” stabilized.
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64.70.pe Metallic glasses
61.43.Fs Glasses
66.20.-d Viscosity of liquids; diffusive momentum transport

Temperature dependent energy level shifts of nitrogen-vacancy centers in diamond

X.-D. Chen, C.-H. Dong, F.-W. Sun, C.-L. Zou, J.-M. Cui, Z.-F. Han, and G.-C. Guo

Appl. Phys. Lett. 99, 161903 (2011); http://dx.doi.org/10.1063/1.3652910 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2011

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Magnetic resonance and fluorescence spectra of nitrogen-vacancy (NV) color centers ensemble in high purity diamond sample were measured, with temperature ranging from 5.6 K to 295 K. Both microwave and optical transition energies have similar nonlinear temperature dependent changes, which might mainly originate from the local thermal expansion. As the frequency shifts will reduce the fidelity of resonant quantum control, the present results demonstrate the necessity of taking temperature fluctuation into consideration. For temperature below 100 K, the transition energies show tendencies to be constant, which indicate higher stability and performance in applications with NV centers.
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61.72.jd Vacancies
78.55.Hx Other solid inorganic materials
61.72.jn Color centers
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
71.20.Tx Fullerenes and related materials; intercalation compounds
76.70.Hb Optically detected magnetic resonance (ODMR)

Three-photon near-infrared quantum splitting in β-NaYF4:Ho3+

D. C. Yu, X. Y. Huang, S. Ye, M. Y. Peng, Q. Y. Zhang, and L. Wondraczek

Appl. Phys. Lett. 99, 161904 (2011); http://dx.doi.org/10.1063/1.3652916 (3 pages) | Cited 7 times

Online Publication Date: 18 October 2011

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We report on three-step sequential three-photon near-infrared (NIR) quantum splitting in β-NaYF4:Ho3+, where one absorbed ultraviolet photon is split into three NIR photons with wavelengths 850, 1015, and 1180 nm. The underlying mechanism is analyzed by static and dynamic photoemission and excitation spectroscopy. An internal quantum yield of 124% is estimated on the basis experimental data and theoretical considerations. Further development of an efficient triply splitting NIR phosphor might open up an approach in achieving efficient photonic devices, which enables more photons emitted than absorbed in the excitation process.
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78.55.Hx Other solid inorganic materials
79.60.-i Photoemission and photoelectron spectra

Anisotropic response of nanosized bismuth films upon femtosecond laser excitation monitored by ultrafast electron diffraction

Ahmed R. Esmail and Hani E. Elsayed-Ali

Appl. Phys. Lett. 99, 161905 (2011); http://dx.doi.org/10.1063/1.3652919 (3 pages) | Cited 1 time

Online Publication Date: 18 October 2011

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The lattice response of 5 nm thick bismuth film to femtosecond laser excitation is probed by ultrafast electron diffraction. The transient decay time after laser excitation is greater for diffraction from (012) lattice planes compared to (110) planes and is reduced for both planes with the increased laser fluence. These results indicate that different energy coupling mechanisms to the lattice occur depending on the crystal direction. The behavior of the diffraction peak width indicates partial disorder of the film upon photoexcitation that increases together with the laser fluence.
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63.20.Ry Anharmonic lattice modes
68.55.aj Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

In situ x-ray study of the formation of defects in Ge islands on Si(001)

M.-I. Richard, T. U. Schülli, and G. Renaud

Appl. Phys. Lett. 99, 161906 (2011); http://dx.doi.org/10.1063/1.3654153 (3 pages) | Cited 1 time

Online Publication Date: 19 October 2011

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Plastic relaxation and formation of defects is a crucial issue in the epitaxial growth of nanoparticles and thin films. Here, we report an in situ non-destructive method based on x-ray diffuse scattering close to forbidden reflections to study the formation of defects during the growth of Ge islands on Si(001). The dependence of in-plane spacing between interfacial dislocations, defect size, and density is analyzed as a function of Ge-deposit. It is found that the introduction of additional defects is preferred to relieve strain during growth.
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81.70.-q Methods of materials testing and analysis
61.72.Lk Linear defects: dislocations, disclinations
78.70.Ck X-ray scattering

Hug-like island growth of Ge on strained vicinal Si(111) surfaces

L. Persichetti, R. Menditto, A. Sgarlata, M. Fanfoni, and A. Balzarotti

Appl. Phys. Lett. 99, 161907 (2011); http://dx.doi.org/10.1063/1.3655906 (3 pages) | Cited 2 times

Online Publication Date: 19 October 2011

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We examine the structure and the evolution of Ge islands epitaxially grown on vicinal Si(111) surfaces by scanning tunneling microscopy. Contrary to what is observed on the singular surface, three-dimensional Ge nanoislands form directly through the elastic relaxation of step-edge protrusions during the unstable step-flow growth. As the substrate misorientation is increased, the islands undergo a shape transformation which is driven by surface energy minimization and controlled by the miscut angle. Using finite element simulations, we show that the dynamics of islanding observed in the experiment results from the anisotropy of the strain relaxation.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Md Surface thermodynamics, surface energies

Effect of the Ti molar ratio on the electrical characteristics of titanium-indium-zinc-oxide thin-film transistors fabricated by using a solution process

Ho Yong Chong, Kyu Wan Han, Young Soo No, and Tae Whan Kim

Appl. Phys. Lett. 99, 161908 (2011); http://dx.doi.org/10.1063/1.3655197 (3 pages) | Cited 6 times

Online Publication Date: 20 October 2011

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Thin film transistors (TFTs) utilizing TiInZnO (TIZO) channel layers with different Ti molar ratios were fabricated by using a solution process. X-ray photoelectron spectroscopy spectra for the TIZO film exhibited that the Ti 2p1/2 peak intensity increased with increasing Ti molar ratio. The addition of the Ti atoms in the TIZO films changed their carrier concentration due to the decrease of O2− ions, resulting in a positive shift of the threshold voltage and in a decrease of the off-current. The on/off current ratio of the TFTs with a 10% Ti molar ratio was as large as 0.21 × 107.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
79.60.Dp Adsorbed layers and thin films

Observation of the Plateau-Rayleigh capillary instability in multi-material optical fibers

S. Shabahang, J. J. Kaufman, D. S. Deng, and A. F. Abouraddy

Appl. Phys. Lett. 99, 161909 (2011); http://dx.doi.org/10.1063/1.3653247 (3 pages) | Cited 4 times

Online Publication Date: 21 October 2011

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We report the observation of the Plateau-Rayleigh capillary instability during the tapering of a multi-material optical fiber. The fiber core is a glass, and the cladding is an amorphous polymer. The instability is manifested in the breakup of the core into a periodic string of size-tunable micro-scale droplets embedded along the fiber axis. The particle diameters may be tuned in the 1–20 μm range through control of the tapering speed and temperature. Extending this approach to the fabrication of polymer and glass nanoparticles appears feasible.
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42.81.Bm Fabrication, cladding, and splicing
42.70.Ce Glasses, quartz
42.70.Jk Polymers and organics
47.55.nb Capillary and thermocapillary flows
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
47.20.-k Flow instabilities
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Effect of interface states on the instability under temperature stress in amorphous SiInZnO thin film transistor

Do Hyung Kim, Hyun Kwang Jung, Dae Hwan Kim, and Sang Yeol Lee

Appl. Phys. Lett. 99, 162101 (2011); http://dx.doi.org/10.1063/1.3645597 (3 pages) | Cited 2 times

Online Publication Date: 17 October 2011

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The instability of amorphous SiInZnO thin-film transistor with different active layer thickness under temperature stress has been investigated using the density of states extracted directly from capacitance-voltage characteristics. Interestingly, it is found that the instability under temperature stress is inversely proportional to the magnitude of interfacial trap density not the total trap density. This was observed from the decrease of the falling rate of activation energy as increasing interfacial trap density. Therefore, the interfacial trap plays a very important role as a key origin for the negative threshold voltage shift under temperature stress in SiInZnO thin-film transistors.
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85.30.Tv Field effect devices

Electrical spin injection and detection at Al2O3/n-type germanium interface using three terminal geometry

A. Jain, L. Louahadj, J. Peiro, J. C. Le Breton, C. Vergnaud, A. Barski, C. Beigné, L. Notin, A. Marty, V. Baltz, S. Auffret, E. Augendre, H. Jaffrès, J. M. George, and M. Jamet

Appl. Phys. Lett. 99, 162102 (2011); http://dx.doi.org/10.1063/1.3652757 (3 pages) | Cited 21 times

Online Publication Date: 18 October 2011

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In this letter, we report on electrical spin injection and detection in n-type germanium-on-insulator using a Co/Py/Al2O3 spin injector and 3-terminal non-local measurements. We observe an enhanced spin accumulation signal of the order of 1 meV consistent with the sequential tunneling process via interface states in the vicinity of the Al2O3/Ge interface. This spin signal is further observable up to 220 K. Moreover, the presence of a strong inverted Hanle effect points out the influence of random fields arising from interface roughness on the injected spins.
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72.25.Mk Spin transport through interfaces
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling

Diffusion of tin in germanium: A GGA+U approach

H. Tahini, A. Chroneos, R. W. Grimes, and U. Schwingenschlögl

Appl. Phys. Lett. 99, 162103 (2011); http://dx.doi.org/10.1063/1.3653472 (3 pages) | Cited 9 times

Online Publication Date: 18 October 2011

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Density functional theory calculations are used to investigate the formation and diffusion of tin-vacancy pairs (SnV) in germanium (Ge). Depending upon the Fermi energy, SnV pairs can form in neutral, singly negative, or doubly negative charged states. The activation energies of diffusion, also as function of the Fermi energy, are calculated to lie between 2.48-3.65 eV, in agreement with and providing an interpretation of available experimental work.
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66.30.J- Diffusion of impurities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Gj Other metals and alloys
61.72.jd Vacancies

Interfacial charge effects on electron transport in III-Nitride metal insulator semiconductor transistors

Ting-Hsiang Hung, Michele Esposto, and Siddharth Rajan

Appl. Phys. Lett. 99, 162104 (2011); http://dx.doi.org/10.1063/1.3653805 (3 pages) | Cited 4 times

Online Publication Date: 18 October 2011

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We report on the calculation of the two dimension electron gas (2DEG) mobility in scaled AlGaN/GaN metal-insulator-semiconductor high-electron-mobility-transistors. We investigate the effect of remote impurity and phonon scattering models on the 2DEG mobility of the dielectric/AlGaN/GaN structure and investigate its variation with dielectric/AlGaN interface charge density, 2DEG concentration, and AlGaN thickness. Remote impurity scattering was found to be the dominant mechanism when the 2DEG density is below 5 × 1012 cm−2 and dielectric/AlGaN interface charge density is above 5 × 1012 cm−2. The interfacial charge has significant effect on the mobility as the AlGaN cap layer thickness is scaled down below 5 nm.
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85.30.Tv Field effect devices

Interaction between Si doping and the polarization-induced internal electric field in the AlGaN/GaN superlattice

Wei Zhang, Yue Zhang, JunShuai Xue, Ying Zhang, Ling Lv, JinCheng Zhang, and Yue Hao

Appl. Phys. Lett. 99, 162105 (2011); http://dx.doi.org/10.1063/1.3655469 (3 pages) | Cited 2 times

Online Publication Date: 20 October 2011

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AlGaN/GaN superlattices (SLs) with and without Si doping exhibit very different properties. Because of the difference between the dielectric constants of AlGaN and GaN, the wells of the SL are depleted in the undoped structure. With increased Si doping in the GaN wells, the depletion effect will vanish, and the accumulation of electrons will compensate for the polarization-induced internal electric field (PIIEF) in the AlGaN barrier, which is followed by disturbance of the PIIEF in the GaN wells due to electron overflow from the ground state E0 to the first excited state E1. This leads to a decrease in E1-E0.
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68.65.Cd Superlattices
73.61.Ey III-V semiconductors
77.22.Ch Permittivity (dielectric function)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Temperature and bias dependence of Hanle effect in CoFe/MgO/composite Ge

Kun-Rok Jeon, Byoung-Chul Min, Youn-Ho Park, Hun-Sung Lee, Chang-Yup Park, Young-Hun Jo, and Sung-Chul Shin

Appl. Phys. Lett. 99, 162106 (2011); http://dx.doi.org/10.1063/1.3648107 (3 pages) | Cited 9 times

Online Publication Date: 20 October 2011

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We have investigated the temperature and bias dependence of the Hanle effect in a composite n-type Ge system consisting of a heavily doped surface layer and a moderately doped Ge substrate, using three-terminal Hanle measurements. A large spin signal of ∼5.1 kΩμm2 and a spin lifetime of ∼105 ps are obtained at 300 K. The spin signal, spin lifetime, and their asymmetries with respect to the bias polarity have been measured over a temperature range from 5 K to 300 K. Intriguingly, an inverted Hanle effect, indicating the sign inversion of spin polarization in Ge, is observed at low temperature.
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72.25.-b Spin polarized transport
73.40.Cg Contact resistance, contact potential
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Tm Composite materials

Graphene p-n junctions with nonuniform Rashba spin-orbit coupling

Marek Rataj and Józef Barnaś

Appl. Phys. Lett. 99, 162107 (2011); http://dx.doi.org/10.1063/1.3641873 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2011

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Linear conductance of graphene-based p-n junctions with Rashba spin-orbit coupling is considered theoretically. A square potential step is used to model the junctions, while the coupling is introduced in terms of the Kane-Mele model (C. L. Kane and E. J. Mele, Phys. Rev. Lett. 95, 226801 (2005)). The main objective is a description of electronic transport in junctions where Rashba parameter is nonuniform. Such a nonuniformity can appear when graphene is asymmetrically covered with atomic layers, or when Rashba coupling is strongly dependent on electric field. It is shown that conductance is significantly modified by the considered nonuniformity, which is most clearly manifested by an anomalous minimum at a certain potential step height.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
72.20.Fr Low-field transport and mobility; piezoresistance
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.25.+i Surface conductivity and carrier phenomena

Shubnikov-de Haas measurement of electron effective mass in GaAs1−xBix

B. Fluegel, R. N. Kini, A. J. Ptak, D. Beaton, K. Alberi, and A. Mascarenhas

Appl. Phys. Lett. 99, 162108 (2011); http://dx.doi.org/10.1063/1.3655198 (3 pages) | Cited 1 time

Online Publication Date: 21 October 2011

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Magnetic field and temperature dependent resistivity measurements on n-type GaAs1-xBix epitaxially grown films show clear Shubnikov de Haas oscillations in the range 0 ≤ x ≤ 0.0088. An overall decrease in the electron effective mass is observed for this range of compositions. Accounting for the known giant bandgap bowing and giant spin orbit bowing, the measured changes in the effective mass are in qualitative agreement with perturbation theory applied to these energy band changes, confirming that bismuth mainly perturbs the valence band. The stronger compositional dependence of the measured mass is attributed to effects from the bismuth isolated state.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Le Other inorganic semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Effect of interfacial oxide layer on the switching uniformity of Ge2Sb2Te5-based resistive change memory devices

Jiyong Woo, Seungjae Jung, Manzar Siddik, Euijun Cha, Sharif Md. Sadaf, and Hyunsang Hwang

Appl. Phys. Lett. 99, 162109 (2011); http://dx.doi.org/10.1063/1.3656247 (3 pages) | Cited 4 times

Online Publication Date: 21 October 2011

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We report the effect of the interfacial oxide layer on switching uniformity in Ge2Sb2Te5 (GST)-based resistive switching memory devices. An interfacial oxide layer acting as an internal resistor was fabricated by the simple thermal oxidation process at low temperature and confirmed by x-ray photoelectron spectroscopy analysis. TiN/oxidized GST/GST/Pt devices showed extremely uniform resistance states owing to intentionally controlled current flow induced by the interfacial oxide layer, despite the filaments being randomly formed. Furthermore, the devices showed good memory performance, e.g., a large on/off resistance ratio (over four orders of magnitude) and reliable data retention (up to 104 s at 85 °C).
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84.30.Sk Pulse and digital circuits
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
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Mode selective parametric excitation of spin waves in a Ni81Fe19 microstripe

T. Brächer, P. Pirro, B. Obry, B. Leven, A. A. Serga, and B. Hillebrands

Appl. Phys. Lett. 99, 162501 (2011); http://dx.doi.org/10.1063/1.3651506 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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We present the experimental observation of parallel parametric amplification of selected thermal spin-wave modes in a transversally magnetized Ni81Fe19 microstripe. By employing Brillouin light scattering microscopy, we identify the dominant group, i.e., the spin-wave mode that is preferentially amplified. Due to the existing spin-wave quantization in the system, it is possible to select one specific mode to be parametrically excited by changing the bias magnetic field. This gives access to transversal spin-wave eigenmodes of the stripe which are promising for spin-wave information processing and also to modes localized at the stripe edges.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Spin pumping by parametrically excited short-wavelength spin waves

H. Kurebayashi, O. Dzyapko, V. E. Demidov, D. Fang, A. J. Ferguson, and S. O. Demokritov

Appl. Phys. Lett. 99, 162502 (2011); http://dx.doi.org/10.1063/1.3652911 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2011

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We use both parallel and perpendicular parametric pumping techniques to excite short-wavelength spin waves in an yttrium iron garnet film and study the spin current generation from spin waves excited by these pumping methods with the help of the inverse spin-Hall effect in the adjacent Pt layer. We observed clear spin current generations for these pumping techniques and find that the efficiency is nearly independent of the magnitude and the direction of the wave vectors of excited spin waves. These experimental results are important for future spintronic devices operated by short-wavelength spin waves.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
72.25.Pn Current-driven spin pumping
75.76.+j Spin transport effects

Micromagnetic modelling of L10-FePt/Ag/L10-FePt pseudo spin valves

P. Ho, R. F. L. Evans, R. W. Chantrell, G. C. Han, G. M. Chow, and J. S. Chen

Appl. Phys. Lett. 99, 162503 (2011); http://dx.doi.org/10.1063/1.3653290 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2011

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A micromagnetic bilayer model, based on the Landau-Lifshitz-Bloch equation, was utilized to study the magnetic, reversal, and spin transport properties of MgO/L10-FePt/Ag/L10-FePt pseudo spin valves. The model simulates a granular bilayer FePt structure and the effects of the Ag spacer were controlled by varying the interlayer exchange strength. Simulation results showed that the reversal of the FePt layers proceeded via reversed domain formation and propagation. Stray fields emanating from the top soft FePt layer reduced the nucleation field of the bottom FePt locally, resulting in the preferential formation of reversed domains at adjacent sites of the bottom hard FePt layer.
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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
75.78.Cd Micromagnetic simulations
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.76.+j Spin transport effects
75.60.Jk Magnetization reversal mechanisms

Magnetocaloric effect contributed by in situ dual-phase structure in the Gd-Co-Al alloy

H. Fu, Q. Zheng, and M. X. Wang

Appl. Phys. Lett. 99, 162504 (2011); http://dx.doi.org/10.1063/1.3652913 (3 pages)

Online Publication Date: 18 October 2011

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In many cases, the presence of secondary phase will deteriorate the magnetocaloric effect of materials due to the difference in magnetic properties. However, the alloy with in situ dual-phase structure and good magnetocaloric effect was found in the pseudo-binary GdCo2-GdAl2 system. Experiments revealed that the GdCo0.65Al1.35 alloy comprised the primary terminal GdAl2 phase and the secondary intermediate GdCo0.74Al1.26 phase. Both of them ordered at 70 K simultaneously. Large magnetic entropy change and relative cooling power of 11.0 J/kg K and 638 J/kg for 0–50 kOe field changes, respectively, were obtained due to the contribution of both GdAl2 and GdCo0.74Al1.26 phases.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Mode conversion by symmetry breaking of propagating spin waves

P. Clausen, K. Vogt, H. Schultheiss, S. Schäfer, B. Obry, G. Wolf, P. Pirro, B. Leven, and B. Hillebrands

Appl. Phys. Lett. 99, 162505 (2011); http://dx.doi.org/10.1063/1.3650256 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2011

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We study spin-wave transport in a microstructured Ni81Fe19 waveguide exhibiting broken translational symmetry. We observe the conversion of a beam profile composed of symmetric spin-wave width modes with odd numbers of antinodes n = 1, 3,… into a mixed set of symmetric and asymmetric modes. Due to the spatial homogeneity of the exciting field along the used microstrip antenna, quantized spin-wave modes with an even number n of antinodes across the stripe’s width cannot be directly excited. We show that a break in translational symmetry may result in a partial conversion of even spin-wave waveguide modes.
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75.30.Ds Spin waves

Josephson amplifier for qubit readout

Baleegh Abdo, Flavius Schackert, Michael Hatridge, Chad Rigetti, and Michel Devoret

Appl. Phys. Lett. 99, 162506 (2011); http://dx.doi.org/10.1063/1.3653473 (3 pages) | Cited 8 times

Online Publication Date: 18 October 2011

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We report on measurements of a Josephson amplifier (J-amp) suitable for quantum-state qubit readout in the microwave domain. It consists of two microstrip resonators which intersect at a Josephson ring modulator. A maximum gain of about 20 dB, a bandwidth of 9 MHz, and a center-frequency tunability of about 60 MHz with gain in excess of 10 dB have been attained for idler and signal of frequencies 6.4 GHz and 8.1 GHz, in accordance with theory. Maximum input power measurements of the J-amp show a relatively good agreement with theoretical prediction. We discuss how the amplifier characteristics can be improved.
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85.25.Cp Josephson devices
84.40.Az Waveguides, transmission lines, striplines
84.30.Le Amplifiers

Structural, magnetic, and magnetotransport properties of NiMnSb thin films deposited by flash evaporation

Nguyen Anh Tuan and Nguyen Phuc Duong

Appl. Phys. Lett. 99, 162507 (2011); http://dx.doi.org/10.1063/1.3651337 (3 pages)

Online Publication Date: 18 October 2011

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To date, the use of flash evaporation (FE) as a deposition technique for NiMnSb thin films has not yet been reported. In this letter, we report on NiMnSb thin films deposited on heated Si (111) substrates at 300 °C via FE. Investigations of the structural characteristics and magnetic and magnetotransport properties of these thin films show typical features of a half-metallic ferromagnetic semi-Heusler alloy. The origin of the film’s extraordinary magnetotransport behavior is examined under the perspective of spin-order levels attached to a grain-grain boundary-type structure.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
75.50.Cc Other ferromagnetic metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars

Jaivardhan Sinha, Masamitsu Hayashi, Yukiko K. Takahashi, Tomohiro Taniguchi, Maksim Drapeko, Seiji Mitani, and Kazuhiro Hono

Appl. Phys. Lett. 99, 162508 (2011); http://dx.doi.org/10.1063/1.3647771 (3 pages) | Cited 5 times

Online Publication Date: 19 October 2011

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We have studied microwave emission from a current-perpendicular-to-plane pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes. Large emission amplitude exceeding 150 nV/Hz0.5, partly owing to the large magnetoresistance, and narrow generation linewidth below 10 MHz are observed. We also find that the linewidth shows significant dependence on the applied field magnitude and its angle within the film plane. A minimum in the linewidth is observed when the slope of the frequency versus current becomes near zero. This agrees with theoretical prediction that takes into account non-linear phase noise as a source for linewidth broadening.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.Np Metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
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