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28 Nov 2011

Volume 99, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 221902 (2011); http://dx.doi.org/10.1063/1.3663578 (3 pages)

Aparna Deshpande, Kai Felix Braun, and Saw-Wai Hla
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Temperature stability of the pentacene thin-film phase

Armin Moser, Jiří Novák, Heinz-Georg Flesch, Tatjana Djuric, Oliver Werzer, Anja Haase, and Roland Resel

Appl. Phys. Lett. 99, 221911 (2011); http://dx.doi.org/10.1063/1.3665188 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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This work presents the influence of temperatures above 300 K on the crystal structure and morphology of pentacene thin films. The thermal expansion of the unit cell and the relative amount of different phases are investigated via grazing incidence x-ray diffraction. Geometrical considerations about the specific molecular packing of the thin-film phase explain the anisotropic non-linear expansion. Furthermore, around 480 K, a phase transformation of the thin-film phase to the bulk phase is observed. In contrast, only a weak influence of the temperature on the height distribution of the thin-film phase crystallites is found.
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68.55.ag Semiconductors
65.40.De Thermal expansion; thermomechanical effects

Interband optical properties of silicon [001] quantum wells using a two-conduction-band k · p model

Fabienne Michelini and Issam Ouerghi

Appl. Phys. Lett. 99, 221912 (2011); http://dx.doi.org/10.1063/1.3663974 (3 pages)

Online Publication Date: 1 December 2011

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Using analytical k · p calculations, we are able to describe the zone-center interband optical properties of Si [001] quantum wells in agreement with first principle calculations. Within the k · p band formalism, we understand how the sp*-like character of the conduction band minimum determines a total anisotropy of the polarization. Similarly, its indirect gap nature generates atomic-scale oscillations of the optical matrix elements, which suggests a giant variability of the absorption. Our results are also in agreement with photoluminescence experiments on ultrathin Si/SiO2 films.
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78.67.De Quantum wells
71.15.-m Methods of electronic structure calculations
73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Rapid growth and formation mechanism of ultrafine structural oxide eutectic ceramics by laser direct forming

H. J. Su, J. Zhang, L. Liu, J. Eckert, and H. Z. Fu

Appl. Phys. Lett. 99, 221913 (2011); http://dx.doi.org/10.1063/1.3664108 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2011

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Melt growth of oxide eutectic is an important and fast-growing research topic in the fields of both applied physics and materials science. Rapid one-step fabrication of melt-grown oxide ceramics with large size is developed using laser direct forming. The near 100% density of Al2O3/YAG eutectic ceramic in situ composite free of pore and cracks is rapidly melted/solidified directly from Al2O3-Y2O3 powder without any preforming or sintering. Uniform three-dimensional network of ultrafine nanostructured eutectic microstructure is obtained. The direct experimental evidence of faceted-nonfaceted eutectic transition at high growth rate is presented and the physical model of the microstructural formation based on atom cluster elementary process is proposed. This technology provides a rapid freeform fabrication of high-performance complex shaped ceramics for various applications.
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81.16.Mk Laser-assisted deposition
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.30.Fb Solidification
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Anisotropy of electron and hole g-factors in (In,Ga)As quantum dots

A. Schwan, B.-M. Meiners, A. Greilich, D. R. Yakovlev, M. Bayer, A. D. B. Maia, A. A. Quivy, and A. B. Henriques

Appl. Phys. Lett. 99, 221914 (2011); http://dx.doi.org/10.1063/1.3665634 (3 pages) | Cited 7 times

Online Publication Date: 1 December 2011

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The g-factor tensors of electron and hole in self-assembled (In,Ga)As/GaAs quantum dots are studied by time-resolved ellipticity measurements in a three dimensional vector magnet system. Both g-factor tensors show considerable deviations from isotropy. These deviations are much more pronounced for the hole than for the electron and are described by different anisotropy factors, which can even have opposite signs.
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71.20.Nr Semiconductor compounds
73.21.La Quantum dots
81.07.Ta Quantum dots
81.16.Dn Self-assembly
78.47.D- Time resolved spectroscopy (>1 psec)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Evaluating the electrical properties of silicon wafer solar cells using hyperspectral imaging of luminescence

Matthew P. Peloso, Jen Sern Lew, Thorsten Trupke, Marius Peters, Roland Utama, and Armin G. Aberle

Appl. Phys. Lett. 99, 221915 (2011); http://dx.doi.org/10.1063/1.3664134 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2011

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A line-imaging spectrometer is used to collect the spectrum of electroluminescence at each point of a multicrystalline silicon wafer solar cell. Characterization of the diffusion lengths of minority charge carriers is developed using a specific feature of the luminescence spectral signature. It is shown that various material and device parameters affecting the luminescence spectral signature may be determined independently. Diffusion length images derived from the proposed hyperspectral method are assessed against diffusion lengths obtained by light beam induced current measurements. Using hyperspectral imaging, diffusion lengths of minority charge carriers in a silicon wafer solar cell can be determined.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Slow light in one dimensional metallic-dielectric photonic crystals due to sign change of the effective dielectric constant

Yun Shen, Guo Ping Yu, and Guo Ping Wang

Appl. Phys. Lett. 99, 221916 (2011); http://dx.doi.org/10.1063/1.3666028 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2011

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We numerically show slow light can be achieved in one dimensional metallic-dielectric photonic crystals as a result of sign change of the effective dielectric constant. Due to the occurrence of slow light, rainbow trapping effect is realizable in chirped one dimensional metallic-dielectric photonic crystals where thicknesses of metal slabs linearly increase. The results imply the potential applications in constructing nanoscale optical buffer, memories, filter, sorter, etc. for high density integration of optical circuits.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)

A strain relief mode at interface of GaSb/GaAs grown by metalorganic chemical vapor deposition

W. Zhou, W. Tang, and K. M. Lau

Appl. Phys. Lett. 99, 221917 (2011); http://dx.doi.org/10.1063/1.3663571 (3 pages) | Cited 1 time

Online Publication Date: 2 December 2011

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An “atomic chain-like” array distinct from interfacial misfit dislocation arrays was characterized at the interface of GaSb/GaAs grown by metalorganic chemical vapor deposition. Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and x-ray energy-dispersive spectroscopy, we obtained the chemical composition of this structure and confirmed significant anion intermixing within the GaAsSb alloy layer at the interface. Atomic-scale HAADF-STEM imaging and geometric phase analysis revealed variations in the local strain field, indicating that the GaAsSb layer can partially relax the lattice misfit strain. Our results indicate that self-organized alloy intermixing during GaSb epilayer growth on GaAs provides strain relief.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.47.Fg Semiconductor surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Quantum Hall-like effect in gated four-terminal graphene devices without magnetic field

Mou Yang, Xian-Jin Ran, Yan Cui, and Rui-Qiang Wang

Appl. Phys. Lett. 99, 222101 (2011); http://dx.doi.org/10.1063/1.3663625 (3 pages) | Cited 2 times

Online Publication Date: 28 November 2011

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We investigate the transport properties of a four-terminal graphene device of which two terminals are beneath a pair of reversal top gate voltages. We find there exists quantum Hall-like effect without magnetic field applied. The curve of Hall conductance versus the Fermi energy shows steps, and the disorder can make the steps clearer. The average length of Hall conductance plateaus is of the order meV for the devices with the terminal widths of the order μm, which is within the scope of the experimental observation. The influences of gate voltage, device dimensions, and dispersion gap are also discussed.
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73.43.-f Quantum Hall effects
72.80.Vp Electronic transport in graphene
73.20.At Surface states, band structure, electron density of states

Localized charge trapping and lateral charge diffusion in metal nanocrystal-embedded High-κ/SiO2 gate stack

Z. Z. Lwin, K. L. Pey, C. Liu, Q. Liu, Q. Zhang, Y. N. Chen, P. K. Singh, and S. Mahapatra

Appl. Phys. Lett. 99, 222102 (2011); http://dx.doi.org/10.1063/1.3664220 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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In this work, we demonstrate a two-step analysis procedure that enables an in-depth understanding of the localized charge trapping and charge decay mechanisms in metal nanocrystal (MNC)-embedded high-κ/SiO2 gate stacks. The results clearly reveal that vertical charge loss and lateral charge diffusion are two competing mechanisms, and they can be identified by discharging current measurements at elevated temperatures and the Kelvin force microscopy characterization. It is found that the MNC with higher work function has a lower inter-dot charge tunneling probability, which is favorable for improved retention in memory applications. However, the vertical charge loss during the initial decay period is a trade-off and it could be minimized by using a dual-layer MNC structure.
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84.30.Sk Pulse and digital circuits
73.63.Bd Nanocrystalline materials

Intrinsic defects and electronic conductivity of TaON: First-principles insights

Shiyou Chen and Lin-Wang Wang

Appl. Phys. Lett. 99, 222103 (2011); http://dx.doi.org/10.1063/1.3664346 (3 pages) | Cited 4 times

Online Publication Date: 28 November 2011

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Using hybrid functional calculations we show that TaON has different defect properties from the binary tantalum oxide and nitride: (i) instead of O or N vacancies or Ta interstitials, the ON antisite is the dominant defect, which determines its intrinsic n-type conductivity and the p-type doping difficulty; (ii) the ON antisite has a shallower donor level than O or N vacancies, with a delocalized distribution composed mainly of the Ta 5d orbitals, which gives rise to better electronic conductivity in the oxynitride than in the oxide and nitride. The phase stability analysis reveals that further oxidation of TaON is possible when the oxygen chemical potential is high (O rich); thus, a low oxygen partial pressure is required to synthesize stoichiometric TaON samples.
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71.55.Ht Other nonmetals
72.80.Sk Insulators
61.72.up Other materials
61.72.jd Vacancies
61.72.jj Interstitials

Effect of H on interface properties of Al2O3/In0.53Ga0.47As

Zuoguang Liu, Sharon Cui, Pini Shekhter, Xiao Sun, Lior Kornblum, Jie Yang, Moshe Eizenberg, K. S. Chang-Liao, and T. P. Ma

Appl. Phys. Lett. 99, 222104 (2011); http://dx.doi.org/10.1063/1.3665395 (3 pages) | Cited 3 times

Online Publication Date: 29 November 2011

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We report that depositing Al2O3 on InGaAs in an H-containing ambient (e.g., in forming gas) results in significant reduction of interface-trap density and significantly suppressed frequency dispersion of accumulation capacitance. The results of the inelastic electron tunneling spectroscopy study reveal that strong trap features at the Al2O3/InGaAs interface in the InGaAs band gap are largely removed by depositing Al2O3 in an H-containing ambient. Transmission electron microscopy images and x-ray photoelectron spectroscopy data shed some light on the role of hydrogen in improving interface properties of the Al2O3/In0.53Ga0.47As gate stack.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Cliff-like conduction band offset and KCN-induced recombination barrier enhancement at the CdS/Cu2ZnSnS4 thin-film solar cell heterojunction

M. Bär, B.-A. Schubert, B. Marsen, R. G. Wilks, S. Pookpanratana, M. Blum, S. Krause, T. Unold, W. Yang, L. Weinhardt, C. Heske, and H.-W. Schock

Appl. Phys. Lett. 99, 222105 (2011); http://dx.doi.org/10.1063/1.3663327 (3 pages) | Cited 7 times

Online Publication Date: 29 November 2011

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The electronic structure of the CdS/Cu2ZnSnS4 (CZTS) heterojunction was investigated by direct and inverse photoemission. The effects of a KCN etch of the CZTS absorber prior to CdS deposition on the band alignment at the respective interface were studied. We find a “cliff”-like conduction band offset at the CdS/CZTS interface independent of absorber pretreatment and a significant etch-induced enhancement of the energetic barrier for charge carrier recombination across the CdS/CZTS interface.
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88.40.H- Solar cells (photovoltaics)
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.-i Photoemission and photoelectron spectra
68.55.ag Semiconductors
88.40.J- Types of solar cells

Anisotropic effect of piezoelectric polarization on Schottky barrier height in elastically deformed bulk GaN crystal

Masaki Fujikane (藤金 正樹), Toshiya Yokogawa (横川 俊哉), Shijo Nagao (長尾 至成), and Roman Nowak

Appl. Phys. Lett. 99, 222106 (2011); http://dx.doi.org/10.1063/1.3665250 (3 pages) | Cited 1 time

Online Publication Date: 30 November 2011

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We studied electrical characteristics in c-pane (0001) and m-plane (10−10) GaN by nanoindentation examination with a conductive diamond indenter. At constant voltage during partial indentation, the current density increased stepwise as the loading–unloading cycle went by in c-plane GaN and was constant in m-plane GaN. During several constant-indentation loads, the turn-on voltage decreased with increasing indentation load in c-plane GaN and was constant in m-plane GaN. We investigated the piezoelectric polarization anisotropy by in situ electric measurement while controlling strain in GaN crystals.
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73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Transport properties in single-crystalline rutile TiO2 nanorods

R. S. Chen, C. A. Chen, W. C. Wang, H. Y. Tsai, and Y. S. Huang

Appl. Phys. Lett. 99, 222107 (2011); http://dx.doi.org/10.1063/1.3665635 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2011

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Electronic transport properties of the single-crystalline titanium dioxide (TiO2) nanorods (NRs) with single rutile phase have been investigated. The conductivity values for the individual TiO2 NRs grown by metal-organic chemical vapor deposition are in the range of 1−10 Ω−1 cm−1. The temperature-dependent measurement shows the presence of two shallow donor levels/bands with activation energies at 8 and 28 meV, respectively. On the photoconductivity (PC), the TiO2 NRs exhibit the much higher normalized PC gain and sensitive excitation-power dependence than the polycrystalline nanotubes. The results demonstrate the superior photoconduction efficiency and distinct mechanism in the monocrystalline one-dimensional TiO2 nanostructures in comparison to the polycrystalline or nanoporous counterparts.
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72.40.+w Photoconduction and photovoltaic effects
73.63.Fg Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
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)
71.55.Ht Other nonmetals

Ab-initio simulations of deformation potentials and electron mobility in chemically modified graphene and two-dimensional hexagonal boron-nitride

Samantha Bruzzone and Gianluca Fiori

Appl. Phys. Lett. 99, 222108 (2011); http://dx.doi.org/10.1063/1.3665183 (3 pages) | Cited 6 times

Online Publication Date: 1 December 2011

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We present an ab-initio study of electron mobility and electron-phonon coupling in chemically modified graphene, considering fluorinated and hydrogenated graphene at different percentage coverage. Hexagonal boron carbon nitrogen is also investigated due the increased interest shown by the research community towards this material. In particular, the deformation potentials are computed by means of density functional theory, while the carrier mobility is obtained according to the Takagi model (S. Takagi, A. Toriumi, and H. Tango, IEEE Trans. Electron Devices 41, 2363 (1994)). We will show that graphene with a reduced degree of hydrogenation can compete, in terms of mobility, with silicon technology.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Wp Fullerenes and related materials
63.22.Rc Phonons in graphene
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
63.20.kd Phonon-electron interactions

Electronic interaction and bipolar resistive switching in copper oxide-multilayer graphene hybrid interface: Graphene as an oxygen ion storage and blocking layer

Bharti Singh, B. R. Mehta, Govind, X. Feng, and Klaus Müllen

Appl. Phys. Lett. 99, 222109 (2011); http://dx.doi.org/10.1063/1.3663971 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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This study reports a bipolar resistive switching device based on copper oxide (CuO)-multilayer graphene (MLG) hybrid interface in complete contrast to the ohmic and rectifying characteristics of junctions based on individual MLG and CuO layers. The observed shift and the occurrence of additional O1s, Cu2p, and C1s core level peaks indicate electronic interaction at the hybrid interfacial layer. Large changes in the resistive switching parameters on changing the ambient conditions from air to vacuum establish the important role of MLG as oxygen ion storage and blocking layer towards the observed resistive switching effect.
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85.65.+h Molecular electronic devices
84.30.Jc Power electronics; power supply circuits
84.32.Dd Connectors, relays, and switches
85.30.Pq Bipolar transistors
85.40.Xx Hybrid microelectronics; thick films

Role of copper in time dependent dielectric breakdown of porous organo-silicate glass low-k materials

Larry Zhao, Marianna Pantouvaki, Kristof Croes, Zsolt Tőkei, Yohan Barbarin, Christopher J. Wilson, Mikhail R. Baklanov, Gerald P. Beyer, and Cor Claeys

Appl. Phys. Lett. 99, 222110 (2011); http://dx.doi.org/10.1063/1.3664405 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2011

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The role of copper in time dependent dielectric breakdown (TDDB) of a porous low-k dielectric with TaN/Ta barrier was investigated on a metal-insulator-metal capacitor configuration where Cu ions can drift into the low-k film by applying a positive potential on the top while they are not permitted to enter the low-k dielectric if a negative potential is applied on the top. No difference in TDDB performance was observed between the positive and negative bias conditions, suggesting that Cu cannot penetrate TaN/Ta barrier to play a critical role in the TDDB of porous low-k material.
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81.05.Kf Glasses (including metallic glasses)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Rm Porous materials; granular materials
84.32.Tt Capacitors
77.55.Bh Low-permittivity dielectric films
77.22.Jp Dielectric breakdown and space-charge effects

Effect of transverse electric field on helical edge states in a quantum spin-Hall system

Genhua Liu, Guanghui Zhou, and Yong-Hai Chen

Appl. Phys. Lett. 99, 222111 (2011); http://dx.doi.org/10.1063/1.3664776 (3 pages) | Cited 4 times

Online Publication Date: 2 December 2011

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We study the electronic band, density distribution, and transport property for a HgTe/CdTe quantum well Hall bar with finite-width in the presence of a transverse electric field. It is found that the electric field can lead to a topological phase transition which controls edge state properties. Interestingly, the chirality of edge states can be modified under electric field, and a sufficient high field can remove the spectrum gap induced by the coupling between the edge states in a narrow Hall bar, restoring quantum spin-Hall effect. These findings may provide a fundamental understanding of topological edge states.
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81.05.Dz II-VI semiconductors
81.07.St Quantum wells
73.63.Hs Quantum wells
73.43.-f Quantum Hall effects
73.21.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
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Rapid mixing: A route to synthesize magnetite nanoparticles with high moment

Mei Fang, Valter Ström, Richard T. Olsson, Lyubov Belova, and K. V. Rao

Appl. Phys. Lett. 99, 222501 (2011); http://dx.doi.org/10.1063/1.3662965 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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We demonstrate the impact of rapid mixing of the precursors in a time scale of milliseconds on the reaction rate and magnetic properties of co-precipitated magnetite with a custom-made mixer. The mixed volume is directed into a desk-top AC susceptometer to monitor the magnetic response from the growing particles in real-time. These measurements indicate that the reaction is mostly completed within a minute. The obtained superparamagnetic nanoparticles exhibit a narrow size distribution and large magnetization (87 Am2 kg−1). Transmission electron micrographs suggest that rapid mixing is the key for better crystallinity and a more uniform morphology leading to the observed magnetization values.
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81.16.-c Methods of micro- and nanofabrication and processing
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Cd Fabrication of magnetic nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
75.30.Cr Saturation moments and magnetic susceptibilities

Boron migration due to annealing in CoFeB/MgO/CoFeB interfaces: A combined hard x-ray photoelectron spectroscopy and x-ray absorption studies

Abdul K. Rumaiz, C. Jaye, J. C. Woicik, Weigang Wang, D. A. Fischer, J. Jordan-Sweet, and C. L. Chien

Appl. Phys. Lett. 99, 222502 (2011); http://dx.doi.org/10.1063/1.3662967 (3 pages) | Cited 2 times

Online Publication Date: 28 November 2011

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We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine structure (NEXAFS) of CoFeB|MgO|CoFeB interfaces as a function of annealing time. Upon annealing, the oxidation state of B changes from predominantly elemental (0 valence) boron in the as deposited sample to higher oxidation in annealed samples as evident from HAXPES spectra. The NEXAFS spectroscopy results showed that upon heating, B species migrate towards the MgO and interact with it. A comparison of the tunnel junction NEXAFS signature with some standards suggests that the B forms a 3-fold coordinated boron compound in the MgO environment and 4-fold coordinated boron resembling Kotoite mineral in the CoFe/MgO interface.
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79.60.-i Photoemission and photoelectron spectra
78.70.Dm X-ray absorption spectra
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing

Tuning magnetoresistance and exchange coupling in ZnO by doping transition metals

Yu-feng Tian, Yong-feng Li, and Tom Wu

Appl. Phys. Lett. 99, 222503 (2011); http://dx.doi.org/10.1063/1.3664116 (3 pages) | Cited 7 times

Online Publication Date: 28 November 2011

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A systematic study focused on the magneto-transport properties of transition metal (Cu or Co) doped ZnO thin films is performed to elucidate the role of doping on tuning the band structure and exchange coupling in wide band gap oxides. Detailed theoretical fittings suggest that the negative magnetoresistance (MR) originates from the spin-dependent scattering due to the high-order sp-d exchange interaction, while the positive MR can be well described by a model invoking two spin split subbands. Our results suggest that with different dopants both the electronic band structure and the exchange coupling in ZnO can be rationally tailored.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.uj III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
75.30.Et Exchange and superexchange interactions
71.20.Nr Semiconductor compounds

Electronic structure and magnetism of Mn dopants in GaN nanowires: Ensemble vs single nanowire measurements

Shokouh S. Farvid, Manu Hegde, Ian D. Hosein, and Pavle V. Radovanovic

Appl. Phys. Lett. 99, 222504 (2011); http://dx.doi.org/10.1063/1.3664119 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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We studied the electronic structure and magnetization of Mn dopants in GaN nanowires at the ensemble and single nanowire levels by near edge x-ray absorption fine structure spectroscopies. The results of single nanowire measurements indicate that Mn adopts tetrahedral coordination in GaN nanowires and has mixed oxidation state (Mn2+/Mn3+), with Mn2+ being in relative majority. Ensemble nanowire spectra suggest co-deposition of Mn secondary phases alongside nanowires. Single nanowire x-ray magnetic circular dichroism indicates intrinsic magnetic ordering of Mn dopants at 300 K. In contrast, as-grown nanowire samples show only residual magnetization, due to nanowire orientation dependence of magnetization.
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81.05.Ea III-V semiconductors
75.75.-c Magnetic properties of nanostructures
78.67.Uh Nanowires
81.07.Gf Nanowires
73.22.-f Electronic structure of nanoscale materials and related systems
75.50.Pp Magnetic semiconductors

Micromagnetic study of current-pulse-induced magnetization switching in magnetic tunnel junctions with antiferromagnetically and ferromagnetically coupled synthetic free layers

Chikako Yoshida, Young Min Lee, Takao Ochiai, Yuji Uehara, and Toshihiro Sugii

Appl. Phys. Lett. 99, 222505 (2011); http://dx.doi.org/10.1063/1.3664225 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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We investigated the dynamics of current-pulse-induced magnetization switching in magnetic tunnel junctions (MTJs) with antiferromagnetically and ferromagnetically coupled synthetic free layers through micromagnetic simulations. We found that a magnetic vortex is formed in thick upper ferromagnetic layers and plays an important role in magnetization switching in both types of synthetic free layers. Furthermore, higher thermal stability is observed in an MTJ with the ferromagnetically coupled free layer at an annealing temperature of 250 °C.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.Cd Micromagnetic simulations
75.78.Jp Ultrafast magnetization dynamics and switching

Tuning exchange bias by thermal fluctuation in Fe52Mn23Ga25 melt-spun ribbons

X. D. Tang, W. H. Wang, G. H. Wu, F. B. Meng, H. Y. Liu, and H. Z. Luo

Appl. Phys. Lett. 99, 222506 (2011); http://dx.doi.org/10.1063/1.3665037 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2011

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In Fe52Mn23Ga25 ribbons, the exchange bias becomes very sensitive to the proportions and sizes of the ferromagnetic (FM) and antiferromagnetic (AFM) phases. With high cooling fields, the AFM clusters with small sizes are embedded in the FM matrix which is kinetically arrested at low temperatures, resulting in a small exchange bias. The arrested FM phase can be dearrested by thermal fluctuation, and simultaneously, the proportion and sizes of AFM clusters increase with a stable unidirectional anisotropy. With different thermal fluctuations, a continuous tuning of exchange bias field from 0.202 kOe to 2.11 kOe is realized.
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75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys

Large photoinduced conductivity reduction in thin films of metallic ferromagnetic manganites

V. N. Smolyaninova, G. Yong, Rajeswari M. Kolagani, Amlan Biswas, H. K. Ermer, K. Wang, and A. Piazza

Appl. Phys. Lett. 99, 222507 (2011); http://dx.doi.org/10.1063/1.3665039 (3 pages) | Cited 3 times

Online Publication Date: 29 November 2011

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This paper reports on a study of photoinduced resistivity changes in thin films of ferromagnetic metallic (FMM) manganites. We have observed a significant increase of resistance in La0.7Ba0.3MnO3 thin film under continuous wave argon ion laser illumination presumably associated with photoinduced demagnetization. Strong dependence of resistance on thermal/illumination history is consistent with the coexistence of two phases: ferromagnetic metallic phase and photoinduced less conductive phase.
Show PACS
73.61.Ng Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
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