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31 Jan 2011

Volume 98, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 053101 (2011); http://dx.doi.org/10.1063/1.3549154 (3 pages)

Minggang Zeng, Lei Shen, Ming Yang, Chun Zhang, and Yuanping Feng
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Real-time direct observation of Li in LiCoO2 cathode material

Rong Huang, Taro Hitosugi, Scott D. Findlay, Craig A. J. Fisher, Yumi H. Ikuhara, Hiroki Moriwake, Hideki Oki, and Yuichi Ikuhara

Appl. Phys. Lett. 98, 051913 (2011); http://dx.doi.org/10.1063/1.3551538 (3 pages) | Cited 15 times

Online Publication Date: 1 February 2011

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The direct observation of light elements such as Li is a challenge even for state-of-the-art electron microscopy techniques because such elements scatter electrons only weakly. Using the annular bright field scanning transmission electron microscopy imaging technique, we have simultaneously visualized columns of Li, O, and Co ions in the lithium-ion battery cathode material LiCoO2, which is one of the most important cathode materials for industrial applications. The annular bright field image exhibits a good signal-to-noise ratio and the image contrast is not reversed as the specimen thickness changes. The direct visualization of light elements in real time with this method represents an important breakthrough in characterizing the active materials in solid-state electrochemical devices.
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88.80.ff Batteries
82.47.Aa Lithium-ion batteries
82.45.Fk Electrodes

Vibrational properties of graphene fluoride and graphane

H. Peelaers, A. D. Hernández-Nieves, O. Leenaerts, B. Partoens, and F. M. Peeters

Appl. Phys. Lett. 98, 051914 (2011); http://dx.doi.org/10.1063/1.3551712 (3 pages) | Cited 12 times

Online Publication Date: 2 February 2011

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The vibrational properties of graphene fluoride and graphane are studied using ab initio calculations. We find that both sp3 bonded derivatives of graphene have different phonon dispersion relations and phonon densities of states as expected from the different masses associated with the attached atoms of fluorine and hydrogen, respectively. These differences manifest themselves in the predicted temperature behavior of the constant-volume specific heat of both compounds.
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63.22.Rc Phonons in graphene
63.20.dk First-principles theory
65.80.Ck Thermal properties of graphene

Structural and electronic characterization of (2,33) bar-shaped stacking fault in 4H-SiC epitaxial layers

Massimo Camarda, Andrea Canino, Antonino La Magna, Francesco La Via, G. Feng, T. Kimoto, M. Aoki, and H. Kawanowa

Appl. Phys. Lett. 98, 051915 (2011); http://dx.doi.org/10.1063/1.3551542 (3 pages) | Cited 3 times

Online Publication Date: 4 February 2011

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Crystallographic, electronic, and energetic analyses of the (2,33) [or (2,3,3,3) in the standard Zhadanov notation] bar-shaped stacking fault, observed in as-grown 4H-SiC epitaxial layers, are presented. The defect has been identified by means of spatially resolved microphotoluminescence (μ-PL) measurements at different emission wavelengths, focusing on the emission peak at 0.3 eV below the conduction band. Low temperature μ-PL measurements have also been performed. The defect has been identified and characterized using high resolution transmission electron microscopy. Experimental results are correlated and validated by the calculations of the Kohn–Sham electronic band structure and the defect formation energy.
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71.20.Nr Semiconductor compounds
78.55.Hx Other solid inorganic materials
61.72.Nn Stacking faults and other planar or extended defects
78.66.Li Other semiconductors
71.55.Ht Other nonmetals
68.37.Og High-resolution transmission electron microscopy (HRTEM)
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Is electron accumulation universal at InN polar surfaces?

Cheng-Tai Kuo (郭承泰), Shih-Chieh Lin (林詩傑), Kai-Kuen Chang (張凱焜), Hung-Wei Shiu (許紘瑋), Lo-Yueh Chang (張羅嶽), Chia-Hao Chen (陳家浩), Shu-Jung Tang (唐述中), and Shangjr Gwo (果尚志)

Appl. Phys. Lett. 98, 052101 (2011); http://dx.doi.org/10.1063/1.3549874 (3 pages) | Cited 8 times

Online Publication Date: 31 January 2011

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Recent experiments indicate the universality of electron accumulation and downward surface band bending at as-grown InN surfaces with polar or nonpolar orientations. Here, we demonstrate the possibility to prepare flatband InN (000math) surfaces. We have also measured the surface stoichiometry of InN surfaces by using core-level photoelectron spectroscopy. The flatband InN (000math) surface is stoichiometric and free of In adlayer. It implies that the removal of In adlayer at the InN (000math) surface leads to the absence of downward surface band bending. On the other hand, the stoichiometric InN (0001) surface still exhibits surface band bending due to the noncentrosymmetry in the wurtzite structure.
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73.20.At Surface states, band structure, electron density of states
68.35.bg Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Nitrogenated amorphous InGaZnO thin film transistor

Po-Tsun Liu, Yi-Teh Chou, Li-Feng Teng, Fu-Hai Li, and Han-Ping Shieh

Appl. Phys. Lett. 98, 052102 (2011); http://dx.doi.org/10.1063/1.3551537 (3 pages) | Cited 7 times

Online Publication Date: 31 January 2011

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This work presents the electrical characteristics of the nitrogenated amorphous InGaZnO thin film transistor (a-IGZO:N TFT). The a-IGZO:N film acting as a channel layer of a thin film transistor (TFT) device was prepared by dc reactive sputter with a nitrogen and argon gas mixture at room temperature. Experimental results show that the in situ nitrogen incorporation to IGZO film can properly adjust the threshold voltage and enhance the ambient stability of a TFT device. Furthermore, the a-IGZO:N TFT has a 44% increase in the carrier mobility and electrical reliability and uniformity also progress obviously while comparing with those not implementing a nitrogen doping process.
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81.05.Gc Amorphous semiconductors
81.15.Cd Deposition by sputtering
85.30.Tv Field effect devices
73.61.Jc Amorphous semiconductors; glasses
61.72.up Other materials

Electronic and transport properties of a nanometer-scale Au/AlN(0001)/Au junction from first-principles

T.-H. Lu and M.-H. Tsai

Appl. Phys. Lett. 98, 052103 (2011); http://dx.doi.org/10.1063/1.3551709 (3 pages) | Cited 1 time

Online Publication Date: 2 February 2011

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A nanometer-scale Au/Al(0001)/Au junction has been studied by first-principles calculation methods. The calculated current density-voltage curve shows Ohmic behavior, switching effect, and negative differential conductance in various bias ranges. The electronic structure shows the existence of an intrinsic band tilt due to the polar nature of the AlN film, which gives rise to the presence of hole states at the N-surface side and interface states at the Al-surface side of the AlN film. The bias induced changes of hole and interface states and the states of the Al and N ions in central layers determine the transport property.
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73.22.-f Electronic structure of nanoscale materials and related systems
73.63.Bd Nanocrystalline materials
71.15.-m Methods of electronic structure calculations

Conductance of kinked nanowires

B. G. Cook and K. Varga

Appl. Phys. Lett. 98, 052104 (2011); http://dx.doi.org/10.1063/1.3551711 (3 pages) | Cited 1 time

Online Publication Date: 2 February 2011

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The conductance properties of kinked nanowires are studied by first-principles transport calculations within a recently developed complex potential framework. Using prototypical examples of monoatomic Au chains as well as small diameter single-crystalline silicon nanowires we show that transmission strongly depends on the kink geometry and one can tune the conductance properties by the kink angle and other geometrical factors. In the case of a silicon nanowire the presence of a kink drastically reduces the conductance.
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81.05.Cy Elemental semiconductors
81.07.Gf Nanowires
81.07.Vb Quantum wires
81.40.Lm Deformation, plasticity, and creep
73.63.Nm Quantum wires
62.20.F- Deformation and plasticity

Room temperature writing of electrically conductive and insulating zones in silicon by nanoindentation

S. Ruffell, K. Sears, J. E. Bradby, and J. S. Williams

Appl. Phys. Lett. 98, 052105 (2011); http://dx.doi.org/10.1063/1.3549191 (3 pages) | Cited 5 times

Online Publication Date: 2 February 2011

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Conventional silicon devices are fabricated in the diamond cubic phase of silicon, so-called Si-I. Other phases of silicon such as Si-XII and Si-III can be formed under pressure applied by nanoindentation and these phases are metastable at room temperature and pressure. We demonstrate in this letter that such phases exhibit different electrical properties to normal (diamond cubic) silicon and exploit this to perform maskless, room temperature, electrical patterning of silicon by writing both conductive and insulating zones directly into silicon substrates by nanoindentation. Such processing opens up a number of potentially new applications without the need for high temperature processing steps.
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81.05.Cy Elemental semiconductors
62.25.-g Mechanical properties of nanoscale systems
85.30.-z Semiconductor devices
81.16.-c Methods of micro- and nanofabrication and processing
73.61.Cw Elemental semiconductors

Suppression of the Ag/Si surface conductivity transition temperature by organic adsorbates

F. Song, L. Gammelgaard, Ph. Hofmann, and J. W. Wells

Appl. Phys. Lett. 98, 052106 (2011); http://dx.doi.org/10.1063/1.3543853 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2011

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We present temperature dependent nanoscale four-contact conductance measurements performed on a submonolayer coverage of cobalt phthalocyanine on Si(111)–(math×math)Ag. The presence of the organic adsorbates suppresses the reversible Ag/Si surface phase transition temperature and reduces the magnitude of the accompanying switching of the surface conductance. The absence of an observable Kondo effect is also discussed in terms of the reported electron transfer between the Ag/Si surface and the Co2+ ion.
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73.40.Ns Metal-nonmetal contacts
73.25.+i Surface conductivity and carrier phenomena
72.60.+g Mixed conductivity and conductivity transitions
68.35.Rh Phase transitions and critical phenomena
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Effects of hole doping in electronic states of La1−xSrxMnO3 probed by magnetic Compton scattering

T. Mizoroki, M. Itou, Y. Taguchi, T. Iwazumi, and Y. Sakurai

Appl. Phys. Lett. 98, 052107 (2011); http://dx.doi.org/10.1063/1.3552683 (3 pages)

Online Publication Date: 3 February 2011

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We have carried out magnetic Compton scattering measurements on polycrystalline samples of the perovskite manganites La1−xSrxMnO3 covering the hole-doping range from x = 0.1 to x = 0.5. Charge and magnetic Compton profiles were measured in order to obtain Compton profiles of spin-wise subbands. By considering the doping-dependency of the subband Compton profiles, we show how the electronic states evolve associated with hole doping. The results indicate that doped holes predominantly enter into the O 2p states in the lightly doped region and the charge transfer occurs from the up-spin Mn 3d to the down-spin Mn 3d states in the heavily doped region.
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71.20.Ps Other inorganic compounds
78.70.Ck X-ray scattering
71.70.-d Level splitting and interactions
61.72.up Other materials

Enhanced annealing of implantation-induced defects in 4H-SiC by thermal oxidation

L. S. Løvlie and B. G. Svensson

Appl. Phys. Lett. 98, 052108 (2011); http://dx.doi.org/10.1063/1.3531755 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2011

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Annealing of the prominent Z1/2 defect in 4H-SiC has been studied after thermal treatment in N2 and O2 atmospheres at 1150 °C subsequent to implantation with MeV Si-ions to doses in the range of (1–4)×108 cm−2. The annealing rate is found to be significantly enhanced under oxidizing conditions, while in N2 atmosphere Z1/2 remains stable. Hence, a substantial lowering of the annealing temperature required for defect removal in 4H-SiC doped by ion-implantation may be expected using oxidizing annealing atmosphere. Concentration versus depth profiles of Z1/2 clearly show that it is annihilated by defect species injected from the SiO2/4H-SiC interface during oxidation. The injection rate of the in-diffusing species is found to be about (1.2±0.2)×106 cm−2 s−1, and the concentration ratio of the injected species relative to the native atoms originally present in the oxidized volume is ∼ 1×10−7. A model where the annihilating species are injected from the surface with a diffusion coefficient of about 10−8 cm2/s yields excellent agreement with the experimental data.
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61.72.Cc Kinetics of defect formation and annealing
81.65.Mq Oxidation
68.35.Fx Diffusion; interface formation
61.72.up Other materials
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Fast magnetization precession observed in L10-FePt epitaxial thin film

S. Mizukami, S. Iihama, N. Inami, T. Hiratsuka, G. Kim, H. Naganuma, M. Oogane, and Y. Ando

Appl. Phys. Lett. 98, 052501 (2011); http://dx.doi.org/10.1063/1.3549704 (3 pages) | Cited 7 times

Online Publication Date: 31 January 2011

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Fast magnetization precession is observed in L10-FePt alloy epitaxial thin films excited and detected by all-optical means. The precession frequency varies from 45 to 65 GHz depending on the applied magnetic field strength and direction, which can be explained by a uniform precession model taking account of first- and second-order uniaxial magnetic anisotropy. The lowest effective Gilbert damping constant has a minimum value of 0.055, which is about half that in Co/Pt multilayers and is comparable to Ni/Co multilayers with perpendicular magnetic anisotropy.
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73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Detecting single nanomagnet dynamics beyond the diffraction limit in varying magnetostatic environments

Z. Liu, R. Brandt, Y. Yahagi, B. Hansen, B. Harteneck, J. Bokor, A. R. Hawkins, and H. Schmidt

Appl. Phys. Lett. 98, 052502 (2011); http://dx.doi.org/10.1063/1.3549302 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2011

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As areal bit density increases, characterizing individual magnetic bits within dense arrays becomes difficult with diffraction-limited optics. We demonstrate that dynamic magneto-optical detection breaks this diffraction limit if the characteristic behavior of a nanomagnet is sufficiently different from its neighbors’. We use far-field time-resolved Kerr microscopy to resolve the high-frequency magnetization dynamics of a single, small (Ø150 nm) nanomagnet within a low-frequency background from an array of large (Ø500 nm) magnets. We use this technique to observe and quantify the effects of magnetostatic interactions on the single magnet dynamics as the intermagnet spacing is varied.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.20.Ls Magneto-optical effects
75.78.Jp Ultrafast magnetization dynamics and switching
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Correlation between saturation magnetization and surface morphological features in Zn1−xCrxO thin films

Y. M. Hu, S. S. Li, and C. H. Chia

Appl. Phys. Lett. 98, 052503 (2011); http://dx.doi.org/10.1063/1.3549696 (3 pages) | Cited 5 times

Online Publication Date: 1 February 2011

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The effect of chromium doping on the defect-induced ferromagnetism of Zn1−xCrxO films was investigated in this study. X-ray diffraction and x-ray photoelectron results confirm Cr substitution at Zn sites in the ZnO host lattice. A parabolic dependence of the saturation magnetization on the stoichiometric variable x was observed. Photoluminescence and magnetic results indicate that magnetic moments in Zn1−xCrxO films stem from Zn vacancies on the film surface or at grain boundaries. As the variation in saturation magnetization is consistent with that in surface morphology, the ferromagnetism in Zn1−xCrxO films is sensitive to the morphological modification caused by Cr doping.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.bg Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Hf II-VI semiconductors

Hysteresis and intermittency in direct-current superconducting quantum interference device with nanobridges fabricated on a thin membrane

Eran Segev, Oren Suchoi, Oleg Shtempluck, Fei Xue, and Eyal Buks

Appl. Phys. Lett. 98, 052504 (2011); http://dx.doi.org/10.1063/1.3549767 (3 pages)

Online Publication Date: 1 February 2011

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This study examined the voltage response of nanobridge-based direct-current superconducting quantum interference devices (dc-SQUIDs) fabricated on a Si3N4 membrane. Such a configuration may help in reducing 1/f noise, which possibly originates from substrate fluctuating defects. Results showed that the poor thermal coupling between the dc-SQUID and the substrate leads to a strong hysteretic response of the superconducting quantum interference device (SQUID) even though it is biased by an alternating current. In addition, when the dc-SQUID is biased near a threshold of spontaneous oscillations, the measured voltage has an intermittent pattern, which depends on the applied magnetic flux threading the loop of the SQUID.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.40.De Noise and chaos
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Large converse magnetoelectric effect in Metglas FeCoBSi and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite

H. C. Xuan, L. Y. Wang, S. C. Ma, Y. X. Zheng, Q. Q. Cao, D. H. Wang, and Y. W. Du

Appl. Phys. Lett. 98, 052505 (2011); http://dx.doi.org/10.1063/1.3549871 (3 pages) | Cited 9 times

Online Publication Date: 1 February 2011

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Converse magnetoelectric (CME) effect is investigated in a FeCoBSi/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 laminated composite by using induction method within different frequencies. A large CME coefficient of 3.05 G/V is observed at the resonance frequency of 76.5 kHz under a low bias magnetic field of 50 Oe. The CME coefficient of the heterostructure is almost constant and exhibits a relatively high value in a wide frequency span of 1–64 kHz. The origin of large CME effect and the advantages of Metglas acting as ferromagnetic layer are discussed in the present paper.
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75.85.+t Magnetoelectric effects, multiferroics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Ferromagnetic carbon materials prepared from polyacrylonitrile

Tetsuji Saito, Daisuke Nishio-Hamane, Shunsuke Yoshii, and Tsutomu Nojima

Appl. Phys. Lett. 98, 052506 (2011); http://dx.doi.org/10.1063/1.3551522 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2011

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We report a ferromagnetic carbon material that is attracted by a permanent magnet. The ferromagnetic carbon material was prepared by pyrolysis of polyacrylonitrile at 1273 K for 1 h. Chemical analysis combined with an energy-dispersive x-ray analysis revealed that the carbon material did not contain any transition metals. The metal-free ferromagnetic carbon material exhibited a saturation magnetization of 1.22 emu/g at room temperature.
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81.20.-n Methods of materials synthesis and materials processing
61.41.+e Polymers, elastomers, and plastics
75.50.Ww Permanent magnets
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Memory-bit selection and recording by rotating fields in vortex-core cross-point architecture

Young-Sang Yu, Hyunsung Jung, Ki-Suk Lee, Peter Fischer, and Sang-Koog Kim

Appl. Phys. Lett. 98, 052507 (2011); http://dx.doi.org/10.1063/1.3551524 (3 pages) | Cited 5 times

Online Publication Date: 1 February 2011

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In one of our earlier studies S.-K. Kim et al., [Appl. Phys. Lett. 92, 022509 (2008)] , we proposed a concept of robust information storage, recording, and readout, which can be implemented in nonvolatile magnetic random-access memories and is based on the energetically degenerated twofold ground states of vortex-core magnetizations. In the present study, we experimentally demonstrate reliable memory-bit selection and recording in vortex-core cross-point architecture, specifically using a two-by-two vortex-state disk array. In order to efficiently switch a vortex core positioned at the intersection of crossed electrodes, two orthogonal addressing electrodes are selected, and then two Gaussian pulse currents of optimal pulse width and time delay are applied. Such tailored pulse-type rotating magnetic fields which occur only at the selected intersection are a prerequisite for a reliable memory-bit selection and low-power-consumption recording of information in the existing cross-point architecture.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials

Dependence of nonlocal Gilbert damping on the ferromagnetic layer type in ferromagnet/Cu/Pt heterostructures

A. Ghosh, J. F. Sierra, S. Auffret, U. Ebels, and W. E. Bailey

Appl. Phys. Lett. 98, 052508 (2011); http://dx.doi.org/10.1063/1.3551729 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2011

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We have measured the size effect in the nonlocal Gilbert relaxation rate in ferromagnet (FM) (tFM)/Cu(3 nm)[/Pt(2 nm)]/Al(3 nm) heterostructures, FM = {Ni81Fe19,Co60Fe20B20,pure Co}. A common behavior is observed for three FM layers where the additional relaxation obeys both a strict inverse power law dependence ΔG = Ktn, n = −1.04±0.06 and a similar magnitude K = 224±40 MHz⋅nm. As the tested FM layers span an order of magnitude in spin diffusion length λSD, the results are in support of spin diffusion rather than nonlocal resistivity as the origin of the effect.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Effect of vanadium deficiency on properties of polycrystalline LaVO3

S. Jamali Gharetape, M. P. Singh, F. S. Razavi, D. A. Crandles, L. Y. Zhao, and K. T. Leung

Appl. Phys. Lett. 98, 052509 (2011); http://dx.doi.org/10.1063/1.3549179 (3 pages)

Online Publication Date: 2 February 2011

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We report the influence of V deficiency on structure, transport, and magnetic properties of polycrystalline LaVO3. Up to 10% V-deficient samples were synthesized using standard solid state chemistry route. Structural and spectroscopic studies show that it intricately modifies lattice parameters and oxidation states of V. Further temperature dependent resistivity data reveal that V deficiency induces an enhancement in the resistivity and activation energy. The paramagnetic moment of these samples depends on net V composition while all samples exhibit a paramagnetic-to-antiferromagnetic transition at about 140 K. These distinct properties are understood owing to the presence of multiple oxidations states of V, predominantly V3+ and V4+, in nonstoichiometric LaVO3.
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61.66.Fn Inorganic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

Direct observation of the spin configurations of vertical Bloch line

JinBae Kim, Hiro Akinaga, and Jongryoul Kim

Appl. Phys. Lett. 98, 052510 (2011); http://dx.doi.org/10.1063/1.3549694 (3 pages)

Online Publication Date: 2 February 2011

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We observed the spin configurations of Bloch lines in a ferromagnetic MnAs film on GaAs(001) by conventional magnetic force microscopy (MFM) and tilt-scanning (TS)-MFM. Due to the high lateral resolution of conventional MFM measurements, we were able to demonstrate the out-of-plane magnetic components within the Bloch line. Through vertical stray magnetic field mapping, the TS-MFM operation was shown to enable the detailed measurement and visualization of the spin configurations of the Bloch lines. This direct observation method of the spin configurations of vertical Bloch line structures allowed us to visualize antiparallel domain structure on the out-of-plane rotation of magnetization.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Magnetoresistance of Fe3O4-graphene-Fe3O4 junctions

Zhi-Min Liao, Han-Chun Wu, Jing-Jing Wang, Graham L. W. Cross, Shishir Kumar, Igor V. Shvets, and Georg S. Duesberg

Appl. Phys. Lett. 98, 052511 (2011); http://dx.doi.org/10.1063/1.3552679 (3 pages) | Cited 3 times

Online Publication Date: 3 February 2011

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The magnetoresistance (MR) of Fe3O4-graphene-Fe3O4 junctions has been experimentally studied at different temperatures. It is found that a barrier exists at the Fe3O4/graphene interface. The existence of the interfacial barrier was further confirmed by the nonlinear I-V characteristics and nonmetallic temperature dependence of the interfacial resistance. Moreover, spin dependent transport at the interfaces contributes −1.6% MR to the whole device at room temperature and can be regulated by an external electric field.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
75.76.+j Spin transport effects
72.25.-b Spin polarized transport
75.75.-c Magnetic properties of nanostructures
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High-speed electret charging using vacuum UV photoionization

Makoto Honzumi, Kei Hagiwara, Yoshinori Iguchi, and Yuji Suzuki

Appl. Phys. Lett. 98, 052901 (2011); http://dx.doi.org/10.1063/1.3548866 (3 pages) | Cited 3 times

Online Publication Date: 1 February 2011

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We propose a high-speed charging method of electrets using vacuum ultraviolet irradiation. Due to a large amount of the ionization current at reduced pressure, it takes only a few seconds to charge 15-μm-thick polymer electret film to the surface potential of −900 V. This charging rate is two orders of magnitudes larger than corona/soft-x-ray charging methods. The purity of N2 gas depends on the charging rate since the O2 quenching mechanisms of exited N2 molecule would exist. No charge decay is observed for 3000 h, which indicates charged electrets are as stable as those by other charging methods.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
73.61.Ph Polymers; organic compounds
77.55.-g Dielectric thin films
61.82.Pv Polymers, organic compounds

Measurement of depth and energy of buried trap states in dielectric films by single electron tunneling force spectroscopy

J. P. Johnson, D. W. Winslow, and C. C. Williams

Appl. Phys. Lett. 98, 052902 (2011); http://dx.doi.org/10.1063/1.3549150 (3 pages) | Cited 1 time

Online Publication Date: 1 February 2011

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Electronic trap states in dielectric materials critically influence the reliability and performance of electronic devices. A method to characterize such states with atomic scale spatial resolution is presented. The method is based on tunneling charge measurements, performed at different voltages and tip-sample gaps, and a tunneling model. When combined with previously demonstrated two-dimensional trap state imaging, this method will provide for three-dimensional imaging of electronic defect states in dielectrics with atomic scale spatial resolution.
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77.55.-g Dielectric thin films
71.55.Ht Other nonmetals
71.20.Ps Other inorganic compounds

Enhancement of tetragonality and role of strontium vacancies in heterovalent doped SrTiO3

A. Tkach, A. Almeida, J. Agostinho Moreira, T. M. Correia, M. R. Chaves, O. Okhay, P. M. Vilarinho, I. Gregora, and J. Petzelt

Appl. Phys. Lett. 98, 052903 (2011); http://dx.doi.org/10.1063/1.3549181 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2011

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Show Abstract
The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼ 1.54 Å is estimated, which is ∼ 7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1−1.5xBixTiO3.
Show PACS
61.72.jd Vacancies
77.80.B- Phase transitions and Curie point
78.30.Hv Other nonmetallic inorganics
61.66.Fn Inorganic compounds
61.72.up Other materials
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