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19 Mar 2012

Volume 100, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 121101 (2012); http://dx.doi.org/10.1063/1.3693413 (4 pages)

Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta
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Oxygen-vacancy and depth-dependent violet double-peak photoluminescence from ultrathin cuboid SnO2 nanocrystals

L. Z. Liu, X. L. Wu, J. Q. Xu, T. H. Li, J. C. Shen, and Paul K. Chu

Appl. Phys. Lett. 100, 121903 (2012); http://dx.doi.org/10.1063/1.3696044 (4 pages) | Cited 4 times

Online Publication Date: 20 March 2012

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A double peak in the violet region between 360 and 400 nm is observed from the photoluminescence spectra acquired from cuboid SnO2 nanocrystals and the energy separation between the two subpeaks increases with nanocrystal size. The phenomenon arises from band edge recombination caused by different in-depth distributions of oxygen vacancies (OVs). Density functional theory calculations disclose that variations in the oxygen vacancies with depth introduce valence-band peak splitting leading to the observed splitting and shift of the double peak.
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61.72.jd Vacancies
78.55.Hx Other solid inorganic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.At Surface states, band structure, electron density of states

Electronic states and photoluminescence of TiO2 nanotubes with adsorbed surface oxygen

L. Z. Liu, W. Xu, X. L. Wu, Y. Y. Zhang, T. H. Chen, and Paul K. Chu

Appl. Phys. Lett. 100, 121904 (2012); http://dx.doi.org/10.1063/1.3695167 (4 pages) | Cited 1 time

Online Publication Date: 20 March 2012

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The electronic states associated with enhanced photocatalytic activity of anodic anatase TiO2 nanotubes (NTs) annealed in N2 and O2 are investigated by photoluminescence (PL). The NTs annealed in N2 show a green peak related to oxygen vacancies and its position blueshifts with deceasing temperature, whereas those annealed in O2 show a double peak at 475–600 nm and the energy separation increases with decreasing temperature. Spectral analysis and density function theory calculation disclose that the double peak results from residual oxygen vacancies and oxygen atoms on the NT wall and the increased energy separation arises from the larger difference between the inner and outer NT stress at low temperature.
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78.67.Ch Nanotubes
78.55.Hx Other solid inorganic materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry
61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing

High performance magnetocaloric perovskites for magnetic refrigeration

Christian R. H. Bahl, David Velázquez, Kaspar K. Nielsen, Kurt Engelbrecht, Kjeld B. Andersen, Regina Bulatova, and Nini Pryds

Appl. Phys. Lett. 100, 121905 (2012); http://dx.doi.org/10.1063/1.3695338 (3 pages) | Cited 11 times

Online Publication Date: 20 March 2012

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We have applied mixed valance manganite perovskites as magnetocaloric materials in a magnetic refrigeration device. Relying on exact control of the composition and a technique to process the materials into single adjoined pieces, we have observed temperature spans above 9 K with two materials. Reasonable correspondence is found between experiments and a 2D numerical model, using the measured magnetocaloric properties of the two materials as input.
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75.30.Sg Magnetocaloric effect, magnetic cooling

Switching nonlinearity in a superconductor-enhanced metamaterial

Cihan Kurter, Philippe Tassin, Alexander P. Zhuravel, Lei Zhang, Thomas Koschny, Alexey V. Ustinov, Costas M. Soukoulis, and Steven M. Anlage

Appl. Phys. Lett. 100, 121906 (2012); http://dx.doi.org/10.1063/1.3696297 (3 pages) | Cited 3 times

Online Publication Date: 21 March 2012

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We demonstrate a nonlinear metamaterial that can be switched between low and high transmission by controlling the power level of the incident beam. The origin of this nonlinear response is the superconducting Nb thin film employed in the metamaterial structure. We show that with moderate RF power of about 22 dBm it is possible to quench the superconducting state as a result of extremely strong current densities at the corners of the metamaterial’s split-ring resonators. We measure a transmission contrast of 10 dB and a change in group delay of 70 ns between the low and high power states.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents

Ratcheting of silicon island electrodes on substrate due to cyclic intercalation

Hamed Haftbaradaran and Huajian Gao

Appl. Phys. Lett. 100, 121907 (2012); http://dx.doi.org/10.1063/1.3696298 (4 pages) | Cited 6 times

Online Publication Date: 22 March 2012

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Analytical and numerical calculations are conducted to demonstrate a ratcheting mechanism of irreversible and accumulative deformation in patterned Si islands on substrates during lithiation/delithiation cycling. It is shown that ratcheting occurs as soon as one allows the yield stress of Si and/or the friction strength of the interface to vary from lithiation to delithiation half-cycles, and that this important failure mode can be avoided by simply reducing the lateral size of the islands below a critical length scale. The present study provides a feasible explanation for the experimentally observed ratcheting in fractured Si films on substrates.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
68.35.Gy Mechanical properties; surface strains

CdSe/CdTe type-II superlattices grown on GaSb (001) substrates by molecular beam epitaxy

Jing-Jing Li, Xinyu Liu, Shi Liu, Shumin Wang, David J. Smith, Ding Ding, Shane R. Johnson, Jacek K. Furdyna, and Yong-Hang Zhang

Appl. Phys. Lett. 100, 121908 (2012); http://dx.doi.org/10.1063/1.3697676 (3 pages) | Cited 1 time

Online Publication Date: 22 March 2012

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CdSe/CdTe superlattices are grown on GaSb substrates using molecular beam epitaxy. X-ray diffraction measurements and cross-sectional transmission electron microscopy images indicate high crystalline quality. Photoluminescence (PL) measurements show the effective bandgap varies with the superlattice layer thicknesses and confirm the CdSe/CdTe heterostructure has a type-II band edge alignment. The valence band offset between unstrained CdTe and CdSe is determined as 0.63 ± 0.06 eV by fitting the measured PL peak positions using the envelope function approximation and the Kronig-Penney model. These results suggest that CdSe/CdTe superlattices are promising candidates for multi-junction solar cells and other optoelectronic devices based on GaSb substrates.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
73.21.Cd Superlattices
68.65.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

InGaN channel high electron mobility transistor structures grown by metal organic chemical vapor deposition

O. Laboutin, Y. Cao, W. Johnson, R. Wang, G. Li, D. Jena, and H. Xing

Appl. Phys. Lett. 100, 121909 (2012); http://dx.doi.org/10.1063/1.3697415 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2012

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High electron mobility transistor (HEMT) structures of AlInGaN/AlN/InGaN/GaN were grown by metal-organic chemical vapor deposition. A combination of low growth rate and high growth temperature during synthesis of the InGaN channel layer led to significant improvement in HEMT electron transport properties. The improvement was correlated with an evolution of both surface roughness and photoluminescence intensity of InGaN. Record electron mobilities from 1070 to 1290 cm2/V·s with associated sheet charge density of ∼2 × 1013 cm−2 were obtained across the InxGa1-xN channel composition range x = 0.05 to 0.10.
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85.30.Tv Field effect devices
68.47.Fg Semiconductor surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

A microstructurally motivated description of the deformation of vertically aligned carbon nanotube structures

Shelby B. Hutchens, Alan Needleman, and Julia R. Greer

Appl. Phys. Lett. 100, 121910 (2012); http://dx.doi.org/10.1063/1.3697686 (4 pages) | Cited 6 times

Online Publication Date: 23 March 2012

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Vertically aligned carbon nanotube’s extreme compliance and mechanical energy absorption/dissipation capabilities are potentially promising aspects of their multi-functionality. Mathematical models have revealed that a hardening-softening-hardening material relation can capture the unique sequential, periodic buckling behavior displayed by vertically aligned carbon nanotubes under uniaxial compression. Yet the physical origins of these models remain unknown. We provide a microstructure-based motivation for such a phenomenological constitutive relation and use it to explore changes in structural response with nanotube volume fraction.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
62.20.mq Buckling
62.20.F- Deformation and plasticity
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Ti10Sb60Te30 for phase change memory with high-temperature data retention and rapid crystallization speed

Min Zhu, Liangcai Wu, Zhitang Song, Feng Rao, Daolin Cai, Cheng Peng, Xilin Zhou, Kun Ren, Sannian Song, Bo liu, and Songlin Feng

Appl. Phys. Lett. 100, 122101 (2012); http://dx.doi.org/10.1063/1.3695036 (4 pages) | Cited 4 times

Online Publication Date: 19 March 2012

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With a high crystallization temperature of 211 °C, Ti10Sb60Te30 phase change material exhibits a data retention of 10-yr at 137 °C, which is much better than that of usual Ge2Sb2Te5. No other phase is formed in Ti10Sb60Te30 film except hexagonal Sb2Te phase. For Ti10Sb60Te30-based phase change memory cell, as short as 6 ns electric pulse can fulfill the Set operation, demonstrating an extremely rapid crystallization speed of Ti10Sb60Te30. The programming cycles can reach 2.2 × 104 with very short Set/Reset pulses of 100 ns/50 ns.
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84.30.Sk Pulse and digital circuits

A switch for epitaxial graphene electronics: Utilizing the silicon carbide substrate as transistor channel

F. Krach, S. Hertel, D. Waldmann, J. Jobst, M. Krieger, S. Reshanov, A. Schöner, and H. B. Weber

Appl. Phys. Lett. 100, 122102 (2012); http://dx.doi.org/10.1063/1.3695157 (3 pages) | Cited 2 times

Online Publication Date: 19 March 2012

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Due to the lack of graphene transistors with large on/off ratio, we propose a concept employing both epitaxial graphene and its underlying substrate silicon carbide (SiC) as electronic materials. We demonstrate a simple, robust, and scalable transistor, in which graphene serves as electrodes and SiC as a semiconducting channel. The common interface has to be chosen such that it provides favorable charge injection. The insulator and gate functionality is realized by an ionic liquid gate for convenience but could be taken over by a solid gate stack. On/off ratios exceeding 44000 at room temperature are found.
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85.30.Tv Field effect devices

Generalized conductivity model for polar semiconductors at terahertz frequencies

J. Lloyd-Hughes

Appl. Phys. Lett. 100, 122103 (2012); http://dx.doi.org/10.1063/1.3695161 (3 pages) | Cited 4 times

Online Publication Date: 19 March 2012

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A theoretical framework is presented that calculates the conductivity of polar semiconductors at terahertz frequencies without resorting to phenomenological fit parameters, using an expression derived from the Boltzmann transport equation. The time-dependent photoconductivity of InAs and the temperature dependent conductivity of n-doped GaAs are found experimentally by terahertz time-domain spectroscopy. The observed deviation from the Drude-Lorentz conductivity in these model systems is accounted for by this approach, which calculates the energy-dependent electron scattering time.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.70.Gq Microwave and radio-frequency interactions

High Si and Ge n-type doping of GaN doping - Limits and impact on stress

S. Fritze, A. Dadgar, H. Witte, M. Bügler, A. Rohrbeck, J. Bläsing, A. Hoffmann, and A. Krost

Appl. Phys. Lett. 100, 122104 (2012); http://dx.doi.org/10.1063/1.3695172 (4 pages) | Cited 7 times

Online Publication Date: 19 March 2012

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We report on GaN n-type doping using silane, germane, and isobutylgermane as Si and Ge dopants, respectively. A significant increase in tensile stress during growth is observed for Si doped samples while this is not the case for Ge doping. In addition, Ge can be doped up to 2.9 × 1020 cm−3, while Si doping leads to 3-D growth already at concentrations around 1.9 × 1019 cm−3. The free carrier concentration was determined by Hall-effect measurements, crystal quality, and structural properties by x-ray diffraction measurements. Additionally, secondary ion mass spectroscopy and Raman measurements were performed demonstrating the high material quality of Ge doped samples.
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61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance

Low energy electron beam induced vacancy activation in GaN

H. Nykänen, S. Suihkonen, L. Kilanski, M. Sopanen, and F. Tuomisto

Appl. Phys. Lett. 100, 122105 (2012); http://dx.doi.org/10.1063/1.3696047 (3 pages) | Cited 5 times

Online Publication Date: 21 March 2012

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Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5–20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degradation of the band-to-band luminescence of the irradiated GaN films is associated with the activation of point defects. The activated defects were identified as in-grown Ga-vacancies. We propose that MOVPE-GaN contains a significant concentration of passive VGa-Hn complexes that can be activated by H removal during low energy electron irradiation.
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61.80.Fe Electron and positron radiation effects
78.70.Bj Positron annihilation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

SiN passivation layer effects on un-gated two-dimensional electron gas density in AlGaN/AlN/GaN field-effect transistors

A. Asgari and L. Faraone

Appl. Phys. Lett. 100, 122106 (2012); http://dx.doi.org/10.1063/1.3696641 (3 pages) | Cited 2 times

Online Publication Date: 21 March 2012

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In this paper, we present a study of SiN passivation layer effects on the two-dimensional electron gas (2DEG) sheet density in unintentionally doped AlGaN/AlN/GaN heterostructures, using a polarization model based on interface charges and a fully numerical calculation. The analysis of our results clearly indicates that there are at least two occupied sub-bands in the 2DEG for passivated AlGaN/AlN/GaN heterostructures, and with increasing passivation layer thickness and AlN interlayer thickness the 2DEG density increases. The comparison of our calculated results with published experimental data is shown to be in a very good agreement.
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85.30.Tv Field effect devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Determination of exciton diffusion lengths in isotopically engineered diamond junctions

J. Barjon, F. Jomard, A. Tallaire, J. Achard, and F. Silva

Appl. Phys. Lett. 100, 122107 (2012); http://dx.doi.org/10.1063/1.3689783 (4 pages) | Cited 1 time

Online Publication Date: 21 March 2012

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A direct observation of exciton diffusion in isotopically engineered 12C/13C diamond junctions is presented. Excitons generated under a focused electron beam in the higher-energy bandgap 13C diamond diffuse and part of them are collected in the lower-energy bandgap 12C diamond, where they recombine. By using cathodoluminescence spectroscopy on samples in cross-section, the recombination intensity is followed as a function of the electron-beam distance to the 12C/13C interface. Exciton diffusion lengths in 13C diamond up to 7.9 µm at 10 K are deduced.
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71.35.-y Excitons and related phenomena
78.60.Hk Cathodoluminescence, ionoluminescence
66.30.-h Diffusion in solids

Self-adaptive electronic contact between graphene and semiconductors

Haijian Zhong, Zhenghui Liu, Gengzhao Xu, Yingmin Fan, Jianfeng Wang, Xuemin Zhang, Liwei Liu, Ke Xu, and Hui Yang

Appl. Phys. Lett. 100, 122108 (2012); http://dx.doi.org/10.1063/1.3696671 (4 pages) | Cited 4 times

Online Publication Date: 22 March 2012

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Understanding the contact properties of graphene on semiconductors is crucial to improving the performance of graphene optoelectronic devices. Here, we show that when graphene is in contact with a semiconductor, the charge carrier transport into graphene leads to a self-adaptive shift of the Fermi level, which tends to lower the barrier heights of the graphene contact to both n- and p-type semiconductors. A theoretical model is presented to describe the charge carrier transport mechanism and to quantitatively estimate the barrier heights. These results can benefit recent topical approaches for graphene integration in various semiconductor devices.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.ue Graphene

Evaluation of freestanding boron-doped diamond grown by chemical vapour deposition as substrates for vertical power electronic devices

R. Issaoui, J. Achard, A. Tallaire, F. Silva, A. Gicquel, R. Bisaro, B. Servet, G. Garry, and J. Barjon

Appl. Phys. Lett. 100, 122109 (2012); http://dx.doi.org/10.1063/1.3697568 (4 pages) | Cited 1 time

Online Publication Date: 22 March 2012

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In this study, 4 × 4 mm2 freestanding boron-doped diamond single crystals with thickness up to 260 μm have been fabricated by plasma assisted chemical vapour deposition. The boron concentrations measured by secondary ion mass spectroscopy were 1018 to 1020 cm−3 which is in a good agreement with the values calculated from Fourier transform infrared spectroscopy analysis, thus indicating that almost all incorporated boron is electrically active. The dependence of lattice parameters and crystal mosaicity on boron concentrations have also been extracted from high resolution x-ray diffraction experiments on (004) planes. The widths of x-ray rocking curves have globally shown the high quality of the material despite a substantial broadening of the peak, indicating a decrease of structural quality with increasing boron doping levels. Finally, the suitability of these crystals for the development of vertical power electronic devices has been confirmed by four-point probe measurements from which electrical resistivities as low as 0.26 Ω cm have been obtained.
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81.10.Bk Growth from vapor
85.30.-z Semiconductor devices
61.72.U- Doping and impurity implantation
52.77.Dq Plasma-based ion implantation and deposition
78.30.Hv Other nonmetallic inorganics
61.66.-f Structure of specific crystalline solids

Design of three-well indirect pumping terahertz quantum cascade lasers for high optical gain based on nonequilibrium Green’s function analysis

Tao Liu, Tillmann Kubis, Qi Jie Wang, and Gerhard Klimeck

Appl. Phys. Lett. 100, 122110 (2012); http://dx.doi.org/10.1063/1.3697674 (4 pages) | Cited 3 times

Online Publication Date: 23 March 2012

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The nonequilibrium Green’s function approach is applied to the design of three-well indirect pumping terahertz (THz) quantum cascade lasers (QCLs) based on a resonant phonon depopulation scheme. The effects of the anticrossing of the injector states and the dipole matrix element of the laser levels on the optical gain of THz QCLs are studied. The results show that a design that results in a more pronounced anticrossing of the injector states will achieve a higher optical gain in the indirect pumping scheme compared to the traditional resonant-tunneling injection scheme. This offers in general a more efficient coherent resonant-tunneling transport of electrons in the indirect pumping scheme. It is also shown that, for operating temperatures below 200 K and low lasing frequencies, larger dipole matrix elements, i.e., vertical optical transitions, offer a higher optical gain. In contrast, in the case of high lasing frequencies, smaller dipole matrix elements, i.e., diagonal optical transitions are better for achieving a higher optical gain.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Adjustable nitrogen-vacancy induced magnetism in AlN

Yu Liu, Liangbao Jiang, Gang Wang, Sibin Zuo, Wenjun Wang, and Xiaolong Chen

Appl. Phys. Lett. 100, 122401 (2012); http://dx.doi.org/10.1063/1.3696023 (3 pages) | Cited 5 times

Online Publication Date: 19 March 2012

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Nitrogen-vacancy-induced magnetism in AlN is investigated both theoretically and experimentally. First-principles calculations reveal that magnetic coupling between the vacancy-induced moments varies with the vacancy concentration. A sizable ferromagnetic coupling for nitrogen vacancies is found. Experimentally, the magnetism manipulation is realized accordingly by introducing vacancies through varying the nitrogen atmosphere in AlN whiskers. The vacancy control may be applicable to other III-V nitride semiconductors in tuning their magnetism.
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61.72.jd Vacancies
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Electrical control of Curie temperature in cobalt using an ionic liquid film

K. Shimamura, D. Chiba, S. Ono, S. Fukami, N. Ishiwata, M. Kawaguchi, K. Kobayashi, and T. Ono

Appl. Phys. Lett. 100, 122402 (2012); http://dx.doi.org/10.1063/1.3695160 (3 pages) | Cited 6 times

Online Publication Date: 19 March 2012

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The electric field effect on magnetization properties and Curie temperature of Co ultra-thin films has been investigated. An electric field is applied to a Co film by using an electric double layer (EDL) formed in a polymer film containing an ionic liquid. The change in the Curie temperature is ∼100 K by applying the gate voltage of ±2 V, suggesting that the observed large modifications of magnetization properties are attributed to the significant change in the Curie temperature, which is induced by a large amount of carrier density control due to the formation of the EDL.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
82.45.Mp Thin layers, films, monolayers, membranes
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.At Metal and metallic alloys

Magnetic properties of ZnFe2O4 ferrite nanoparticles embedded in ZnO matrix

N. Guskos, S. Glenis, G. Zolnierkiewicz, J. Typek, P. Berczynski, A. Guskos, D. Sibera, and U. Narkiewicz

Appl. Phys. Lett. 100, 122403 (2012); http://dx.doi.org/10.1063/1.3696024 (3 pages) | Cited 1 time

Online Publication Date: 20 March 2012

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Two magnetic nanocomposites were prepared from nanocrystalline zinc oxide doped with different concentrations of iron oxide (5 and 10 wt. %). X-ray diffraction and scanning electron microscopy have shown the growth of ZnFe2O4 nanocrystallites with size below 10 nm within the ZnO matrix in a highly agglomerated structure. Ferromagnetic resonance (FMR) measurements have shown line arising from the ZnFe2O4 nanoparticles. Temperature dependence of the FMR spectra parameters (amplitude, resonance field, linewidth, integrated intensity) has been investigated in the 4–300 K range. Zero-field cooled and field-cooled dc magnetic magnetization study in the same temperature range allowed to determine the blocking temperature TB and compare the results of two applied magnetic methods. Temperature dependence of FMR integrated intensity curve displays a peak at TB ∼ 23 K while FMR amplitude curve peaks at TC ∼ 170 K, the Curie-Weiss temperature of the high temperature susceptibility.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Pp Magnetic semiconductors
75.50.Gg Ferrimagnetics

Micromagnetic analysis of switching and domain structure in amorphous metallic nanowires

Laurentiu Stoleriu, Ciprian Pinzaru, and Alexandru Stancu

Appl. Phys. Lett. 100, 122404 (2012); http://dx.doi.org/10.1063/1.3696046 (4 pages) | Cited 1 time

Online Publication Date: 20 March 2012

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This paper describes a comprehensive micromagnetic model for the observed complex magnetic domains structures in amorphous wires with positive and negative magnetostriction with or without a glass cover. Many experimental studies and theoretical analysis have suggested several typical domain structures. We show the results of micromagnetic simulations that cover many of these observed data using a single set of physical hypotheses.
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75.60.Ch Domain walls and domain structure
81.07.Gf Nanowires
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.78.Cd Micromagnetic simulations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
FREE

Electric field effects in low resistance CoFeB-MgO magnetic tunnel junctions with perpendicular anisotropy

H. Meng, R. Sbiaa, M. A. K. Akhtar, R. S. Liu, V. B. Naik, and C. C. Wang

Appl. Phys. Lett. 100, 122405 (2012); http://dx.doi.org/10.1063/1.3695168 (3 pages) | Cited 8 times

Online Publication Date: 20 March 2012

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We have investigated the electric field effects in low resistance perpendicular magnetic tunnel junction (MTJ) devices and found that the electric field can effectively reduce the coercivity (Hc) of free layer (FL) by 30% for a bias voltage Vb = −0.2 V. In addition, the bias field (Hb) on free layer is almost linearly dependent on Vb yet independent on the device size. The demonstrated Vb dependences of Hc and Hb in low resistance MTJ devices present the potential to extend the scalability of the electric field assisted spin transfer torque magnetic random access memory and improve its access speed.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Long-lived, room-temperature electron spin coherence in colloidal CdS quantum dots

D. H. Feng, X. Li, T. Q. Jia, X. Q. Pan, Z. R. Sun, and Z. Z. Xu

Appl. Phys. Lett. 100, 122406 (2012); http://dx.doi.org/10.1063/1.3696069 (4 pages) | Cited 2 times

Online Publication Date: 21 March 2012

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Time-resolved Faraday rotation spectroscopy is used to study the electron spin coherence in colloidal CdS quantum dots. Long-lived spin coherence with dephasing time T2*>3ns has been found at room temperature. Spin dynamics unaffected by the faster carrier recombination suggests the spin signal coming from the residual electrons in the dots. A small external transverse magnetic field of 50 mT can extend T2* ∼ 2 times longer compared with that in zero magnetic field. Hyperfine interaction between electron and nuclear spins limits the dephasing time in zero or low magnetic field, while for higher magnetic fields, inhomogeneous dephasing becomes to dominate the spin dynamics.
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78.67.Hc Quantum dots
78.20.Ls Magneto-optical effects
78.47.D- Time resolved spectroscopy (>1 psec)
82.70.Dd Colloids
71.70.Jp Nuclear states and interactions

Mechanically tunable magnetic properties of Fe81Ga19 films grown on flexible substrates

Guohong Dai, Qingfeng Zhan, Yiwei Liu, Huali Yang, Xiaoshan Zhang, Bin Chen, and Run-Wei Li

Appl. Phys. Lett. 100, 122407 (2012); http://dx.doi.org/10.1063/1.3696887 (4 pages) | Cited 2 times

Online Publication Date: 21 March 2012

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We investigated on magnetic properties of magnetostrictive Fe81Ga19 films grown on flexible polyethylene terephthalate (PET) substrates under various mechanical strains. The unstrained Fe81Ga19 films exhibit a significant uniaxial magnetic anisotropy due to a residual stress in PET substrates. It was found that the squareness of hysteresis loops can be tuned by an application of strains, inward/compressive or outward/tensile bending of the films. A modified Stoner-Wohlfarth model with considering a distribution of easy axes in polycrystalline films was developed to account for the mechanically tunable magnetic properties in flexible Fe81Ga19 films. These results provide an alternative way to tune mechanically magnetic properties, which is particularly important for developing flexible magnetoelectronic devices.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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