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2 Jul 2012

Volume 101, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 013701 (2012); http://dx.doi.org/10.1063/1.4730945 (5 pages)

Frederick Gertz, Rustam Azimov, and Alexander Khitun
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Sharp acoustic multipolar-resonances in highly monodisperse emulsions

Thomas Brunet, Simon Raffy, Benoit Mascaro, Jacques Leng, Régis Wunenburger, Olivier Mondain-Monval, Olivier Poncelet, and Christophe Aristégui

Appl. Phys. Lett. 101, 011913 (2012); http://dx.doi.org/10.1063/1.4733615 (4 pages) | Cited 1 time

Online Publication Date: 6 July 2012

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We report the achievement of highly monodisperse emulsions exhibiting about ten acoustic Mie resonances. Thanks to robotics, the effective acoustic properties of such strongly scattering media can be precisely targeted by means of the production of calibrated (random) liquid-droplets. Ultrasonic experiments are compared, with an excellent quantitative agreement, to theoretical predictions derived within the framework of the independent scattering approximation. The dependence of the sound speed and of the acoustic attenuation on both the size and the volume fraction of droplets is quantitatively examined for dilute and more concentrated emulsions, and is presented in a dimensionless way.
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82.70.Kj Emulsions and suspensions
47.57.Bc Foams and emulsions
43.25.Gf Standing waves; resonance
47.55.dd Bubble dynamics
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
62.60.+v Acoustical properties of liquids

Abnormal electronic transition variations of lanthanum-modified lead zironate stannate titanate ceramics near morphotropic phase boundary: A spectroscopic evidence

X. Chen (陈啸), K. Jiang (姜凯), Z. G. Hu (胡志高), X. F. Chen (陈学锋), G. S. Wang (王根水), X. L. Dong (董显林), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 101, 011914 (2012); http://dx.doi.org/10.1063/1.4733683 (5 pages)

Online Publication Date: 6 July 2012

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The structure-related optical response of (Pb1-1.5xLax)(Zr0.42Sn0.40Ti0.18)O3 (100x/42/40/18) ceramics with different compositions has been investigated. Based on x-ray diffraction, the phase transition from rhombohedral to tetragonal structure is revealed between compositions of x = 2.6% and 2.8% near morphotropic phase boundary (MPB). Correspondingly, abnormal spectral response in the photon energy from 1.4 to 6.1 eV is observed near MPB. Furthermore, the blue shift of the two critical points related parameters, which is obtained from fitting the reflectance spectra, indicates that the variation of electronic band structure near MPB is responsible for the anomalous behavior.
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71.20.Ps Other inorganic compounds
61.66.Fn Inorganic compounds
71.30.+h Metal-insulator transitions and other electronic transitions
78.40.Ha Other nonmetallic inorganics
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Cg PZT ceramics and other titanates
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Interface roughness scattering in ultra-thin N-polar GaN quantum well channels

Uttam Singisetti, Man Hoi Wong, and Umesh K. Mishra

Appl. Phys. Lett. 101, 012101 (2012); http://dx.doi.org/10.1063/1.4732795 (4 pages)

Online Publication Date: 2 July 2012

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In this Letter, we report experimental and theoretical investigations on the effect of the channel thickness on the low-field electron mobility in N-polar GaN quantum well channels. From temperature dependent Hall mobility data and numerical modeling of the mobility, the interface roughness is identified as a strong factor in determining the low field mobility as the channel thickness is scaled down. In the graded AlGaN back-barrier N-polar GaN field effect transistor structures studied here, the roughness leads to localization of electrons at a channel thickness of 3.5 nm leading to extremely low mobility.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
85.30.Tv Field effect devices
68.35.Ct Interface structure and roughness

Resistive switching behavior of a thin amorphous rare-earth scandate: Effects of oxygen content

W. Z. Chang, J. P. Chu, and S. F. Wang

Appl. Phys. Lett. 101, 012102 (2012); http://dx.doi.org/10.1063/1.4732079 (4 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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In addition to beneficial ∼3 orders of magnitude in the resistance ratio, the amorphous HoScOx film exhibits excellent resistive switching (RS) properties of low electrical stress, thin thickness (36 nm), and simple process without forming or annealing, making it potentially useful for nonvolatile memory applications. Obvious oxygen effects are seen: no apparent RS property is detected in the near-stoichiometric film with 57.6 at. % oxygen, whereas distinct RS characteristics are observed in the oxygen-deficient (50.7 at. %) film. The RS property obtained is thought to be dominated by the high oxygen vacancy concentration, which serves as the filamentary conduction in the sample.
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73.61.Ng Insulators
68.55.jd Thickness
61.43.Er Other amorphous solids
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

On the radiation hardness of (Mg,Zn)O thin films grown by pulsed-laser deposition

Florian Schmidt, Holger von Wenckstern, Daniel Spemann, and Marius Grundmann

Appl. Phys. Lett. 101, 012103 (2012); http://dx.doi.org/10.1063/1.4733358 (4 pages)

Online Publication Date: 3 July 2012

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We report on electrical properties and the generation of the E4 defect in pulsed-laser deposited MgxZn1−xO thin films irradiated with 2.25 MeV protons. Whereas the electrical properties of the Schottky diodes as well as the net doping density of the samples did not change due to irradiation, the concentration of the E4 defect increased proportional to the applied dose as revealed by deep level transient spectroscopy. The generation rate η, is for binary ZnO thin films about 40  cm−1, a factor of 3 higher than in melt-grown single crystals, and increases to about 100  cm−1 for the Mg-alloyed thin films.
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81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
85.30.Kk Junction diodes
68.55.ag Semiconductors
61.80.Jh Ion radiation effects
73.61.Ga II-VI semiconductors

Fast detection of single-charge tunneling to a graphene quantum dot in a multi-level regime

T. Müller, J. Güttinger, D. Bischoff, S. Hellmüller, K. Ensslin, and T. Ihn

Appl. Phys. Lett. 101, 012104 (2012); http://dx.doi.org/10.1063/1.4733613 (4 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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In situ-tunable radio-frequency reflectometry is used for fast charge-detection measurements on a graphene single quantum dot. The variable capacitance of our special matching network both grants tunability and compensates for the large stray capacitance between the charge sensor’s contacts and the doped silicon oxide backgate. To demonstrate the high detection bandwidth thus achieved, the rates for tunneling into and out of the dot through the same barrier are determined. Finally, an analytical model for calculating these rates in the multi-level tunneling regime is presented and found to correspond very well to our experimental observations.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots
73.21.La Quantum dots

Optical properties of ultrathin InAs quantum-well-heterostructures

R. Samti, F. Raouafi, M. Chaouach, M. Maaref, A. Sakri, J. Even, J.-M. Gerard, and J.-M Jancu

Appl. Phys. Lett. 101, 012105 (2012); http://dx.doi.org/10.1063/1.4731783 (3 pages)

Online Publication Date: 5 July 2012

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Band structure calculations of complete InAs monolayer in AlGaAs/GaAs quantum wells are performed within the framework of the extended-basis sp3d5s* tight-binding model. We show that the optical properties can be tuned from the quantum well energy below the GaAs band-gap depending on the well thickness and the position of the probe. The results are supported by differential reflectivity measurements and represent a concept for optoelectronic devices with an operation wavelength widely tuneable around 850 nm employing GaAs process technology.
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78.67.De Quantum wells
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.30.Fs III-V and II-VI semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Nr Semiconductor compounds

Effects of rapid thermal annealing on GaAs1-xBix alloys

A. R. Mohmad, F. Bastiman, C. J. Hunter, R. Richards, S. J. Sweeney, J. S. Ng, and J. P. R. David

Appl. Phys. Lett. 101, 012106 (2012); http://dx.doi.org/10.1063/1.4731784 (3 pages) | Cited 3 times

Online Publication Date: 5 July 2012

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The effects of rapid thermal annealing on the optical and structural properties of GaAs1-xBix alloys for x ranging from 0.022 to 0.065 were investigated. At room temperature, the annealed GaAs1-xBix showed modest improvement (∼3 times) in photoluminescence (PL) while the PL peak wavelength remained relatively unchanged. It was found that bismuth related defects are not easily removed by annealing and the PL improvement may be dominated by the reduction of other types of defects including arsenic and gallium related defects. Also, the optimum annealing temperature is Bi composition dependent. For samples with x < 0.048, the optimum annealing temperature is 700 °C but reduces to 600 °C for higher compositions.
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61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
61.66.Fn Inorganic compounds
78.55.Cr III-V semiconductors

Effect of metals and annealing on specific contact resistivity of GeTe/metal contacts

E. K. Chua, R. Zhao, L. P. Shi, T. C. Chong, T. E. Schlesinger, and J. A. Bain

Appl. Phys. Lett. 101, 012107 (2012); http://dx.doi.org/10.1063/1.4732787 (4 pages) | Cited 1 time

Online Publication Date: 6 July 2012

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The circular transfer length method was employed to extract the specific contact resistivity, ρc of GeTe (amorphous and crystalline state) with metals (Ni, W, TiW) to quantify the series contact resistance. The ρc of amorphous-GeTe with metals was also determined for different annealing conditions. Higher metal work functions produce lower ρc for both GeTe states and the ρc was reduced further for annealing temperatures greater than the GeTe crystallization temperature. This is suggested to be a consequence of the higher temperature required to diffuse sufficient interstitial metallic atoms to transform the GeTe covalent bonding at the interface to metallic bonding.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing
73.30.+y Surface double layers, Schottky barriers, and work functions
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Magnetoresistance and magnetocaloric properties involving strong metamagnetic behavior in Fe-doped Ni45(Co1−xFex)5Mn36.6In13.4 alloys

L. Chen, F. X. Hu, J. Wang, L. F. Bao, J. R. Sun, B. G. Shen, J. H. Yin, and L. Q. Pan

Appl. Phys. Lett. 101, 012401 (2012); http://dx.doi.org/10.1063/1.4732525 (4 pages) | Cited 3 times

Online Publication Date: 2 July 2012

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Here, we report the co-substitution of Fe and Co for Ni atoms on metamagnetic behavior, martensitic transformation, and transport and magnetocaloric properties in Ni45(Co1−xFex)5Mn36.6In13.4 (x = 0∼0.05) alloys. It is found that the introduction of Fe atoms stabilizes martensitic phase and shifts martensitic temperature (TM) to higher temperature. Meanwhile, the Curie temperature TC of parent phase notably decreases. Upon Fe doping, the low magnetization of martensitic phase keeps nearly unchanged while the magnetization of parent phase slightly decreases. As a result, the Fe-doped samples maintain strong metamagnetic behavior and show great MR and MCE in an extended temperature range around room temperature. The hysteresis loss is reduced upon Fe-doping, which leads to an enhancement of effective RC by 15%.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.30.Kf Martensitic transformations

Magnetic and dielectric properties of Aurivillius phase Bi6Fe2Ti3O18 and the doped compounds

J. Yang, L. H. Yin, Z. Liu, X. B. Zhu, W. H. Song, J. M. Dai, Z. R. Yang, and Y. P. Sun

Appl. Phys. Lett. 101, 012402 (2012); http://dx.doi.org/10.1063/1.4732526 (4 pages) | Cited 1 time

Online Publication Date: 2 July 2012

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The magnetic and dielectric properties of Bi6Fe2Ti3O18, Bi6FeCoTi3O18, and Bi5LaFeCoTi3O18 are investigated. The room-temperature ferromagnetism is observed in the samples Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 compared with the paramagnetic behavior in Bi6Fe2Ti3O18 at room temperature. The ferromagnetism in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 can be ascribed to spin canting of the Fe-based and Co-based sublattices via the antisymmetric Dzyaloshinskii-Moriya interaction. The frequency-dependent behavior of the dielectric loss peak in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 manifests itself a thermally activated relaxation process. The rather large activation energy (2.62 ± 0.11 eV for Bi6FeCoTi3O18 and 1.97 ± 0.07 eV for Bi5LaFeCoTi3O18) implies that the relaxation process is not due to the thermal motion of oxygen vacancies inside ceramics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
77.22.Gm Dielectric loss and relaxation
61.72.jd Vacancies
61.72.U- Doping and impurity implantation

Demonstration of magnetoelectric effect in ultrathin Cr2O3/Fe2O3 nano-oxide layer by training effect

Naoki Shimomura, Kazuya Sawada, Tomohiro Nozaki, Masaaki Doi, and Masashi Sahashi

Appl. Phys. Lett. 101, 012403 (2012); http://dx.doi.org/10.1063/1.4731274 (4 pages)

Online Publication Date: 3 July 2012

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We identified magnetoelectric effect in an ultrathin (Cr2O3/Fe2O3) nano-oxide layer structure (thickness ∼1 nm) formed on the surface of a Co0.9Fe0.1 metal layer by investigating the training effect as a function of sense current/bias voltage and its direction. A system-dependent constant κMR, which reflects changes in the surface spin, increases (decreases) with increasing current in the pinned (inverse pinned) direction. Furthermore, κMR varies for temperatures up to ∼200 K with current despite the extreme thinness, thus suggesting the current contributes to the surface spin changes. The results indicate the demonstration of the magnetoelectric effect in ultrathin Cr2O3.
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77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics

Spin-polarized scanning tunneling microscopy study of Mn/Co/Cu(001) using a bulk Fe ring probe

Chii-Bin Wu (吳啟彬), Jiaming Song (宋佳明), and Wolfgang Kuch

Appl. Phys. Lett. 101, 012404 (2012); http://dx.doi.org/10.1063/1.4733343 (5 pages)

Online Publication Date: 3 July 2012

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A bulk ring probe made of pure iron wire with diameter of 0.125 mm was prepared for spin-polarized scanning tunneling microscopy at room temperature in ultrahigh vacuum. The layerwise antiferromagnetic spin contrast of 2.8 atomic monolayers (ML) Mn/4.5 ML Co/Cu(001) observed with such a probe revealed a spin asymmetry of 14% and a signal-to-noise ratio of 1.8. Areas of reversed spin contrast on the same atomic layer of Mn were observed and attributed to the influence from underlying Co steps and islands. This demonstrates the simplicity of preparation and capability of such bulk Fe ring probes.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films

Long coherence time of spin qubits in 12C enriched polycrystalline chemical vapor deposition diamond

K. D. Jahnke, B. Naydenov, T. Teraji, S. Koizumi, T. Umeda, J. Isoya, and F. Jelezko

Appl. Phys. Lett. 101, 012405 (2012); http://dx.doi.org/10.1063/1.4731778 (5 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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Single defects in diamond and especially negatively charged nitrogen vacancy (NV) centers are very promising quantum systems with wide applications in physics and biology. It was shown that their coherence properties can be strongly improved by growing ultrapure diamond with low concentration of parasitic spins associated with nitrogen electron spins and nuclear spins related to 13C carbon isotope. Here we report a high quality 12C-enriched polycrystalline chemical vapor deposition diamond material with properties comparable with single crystals. We find single NVs in the grains of this material, which show extremely long electron spin coherence time T2>2ms.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
03.67.Lx Quantum computation architectures and implementations
61.72.jd Vacancies

Chemical diffusion: Another factor affecting the magnetoresistance ratio in Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junction

Y. Yang, W. X. Wang, Y. Yao, H. F. Liu, H. Naganuma, T. S. Sakul, X. F. Han, and R. C. Yu

Appl. Phys. Lett. 101, 012406 (2012); http://dx.doi.org/10.1063/1.4732463 (3 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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This letter investigates the microstructure and mean inner potential (MIP) profile of Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junctions (MTJs) by high resolution transmission electron microscopy (HRTEM) and electron holography, respectively. The inconspicuous crystallization of MgO barrier is confirmed by HRTEM in the post-annealed sample at 250 °C. An obvious MIP difference is displayed in the Ta layers between the top and bottom of the MTJ, and elemental content difference of them is confirmed by energy dispersive spectroscopy. These results imply that the chemical diffusion can also give rise to a lower tunnel magnetoresistance ratio besides the inconspicuous crystallization of MgO barrier.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
66.30.Ny Chemical interdiffusion; diffusion barriers

Exchange bias and its thermal stability in ferromagnetic/antiferromagnetic antidot arrays

W. J. Gong, W. J. Yu, W. Liu, S. Guo, S. Ma, J. N. Feng, B. Li, and Z. D. Zhang

Appl. Phys. Lett. 101, 012407 (2012); http://dx.doi.org/10.1063/1.4733341 (4 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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The exchange bias (EB) effect and its thermal stability in nanoscale Co/NiO antidot arrays and sheet films have been investigated. The EB field HE increases with increasing Co thickness (tCo) and reaches a maximum at tCo = 8 nm in the antidot arrays, whereas HE decreases with tCo in the sheet films. Compared with the sheet films, HE in the antidot arrays is either enhanced or decreased, depending on the thickness of the ferromagnetic Co layer, which is due to the three-dimensional effects in the antiferromagnetic NiO and ferromagnetic Co layers caused by the nanopores. A higher thermal stability is observed in the antidot arrays due to the out-of-plane anisotropy constant K1 of the misaligned antiferromagnetic magnetization component.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures

Domain-related origin of magnetic relaxation in compressively strained manganite thin films

S. R. Bakaul, B. F. Miao, W. Lin, W. Hu, A. David, H. F. Ding, and T. Wu

Appl. Phys. Lett. 101, 012408 (2012); http://dx.doi.org/10.1063/1.4733320 (4 pages) | Cited 4 times

Online Publication Date: 6 July 2012

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Magnetic relaxation is ubiquitous in magnetic materials, and elucidation of the underlying mechanisms is important for achieving reliable device operations. Here, we systematically investigate the magnetic relaxation in compressively strained La0.7Sr0.3MnO3 thin films. Upon the removal of external magnetic field, the slow time-dependent increase of in-plane magnetization is correlated with the break-up of magnetic domains and the emergence of additional domain walls, whereas a reduction of magnetization for the initial short period dominates the magnetic relaxation at lower temperatures in thinner films. These relaxation effects underline the importance of domain dynamics in the properties of magnetic thin films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.78.Fg Dynamics of domain structures
75.60.Ch Domain walls and domain structure

Magnetic properties of Co2C and Co3C nanoparticles and their assemblies

Kyler J. Carroll, Zachary J. Huba, Steven R. Spurgeon, Meichun Qian, Shiv N. Khanna, Daniel M. Hudgins, Mitra L. Taheri, and Everett E. Carpenter

Appl. Phys. Lett. 101, 012409 (2012); http://dx.doi.org/10.1063/1.4733321 (5 pages) | Cited 2 times

Online Publication Date: 6 July 2012

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Nano-composite material consisting of Co2C and Co3C nanoparticles has recently been shown to exhibit unusually large coercivities and energy products. Experimental studies that can delineate the properties of individual phases have been undertaken and provide information on how the coercivities and the energy product change with the size and composition of the nanoparticles. The studies indicate that while both phases are magnetic, the Co3C has higher magnetization and coercivity compared to Co2C. Through first principles electronic structure studies using a GGA+U functional, we provide insight on the role of C intercalation on enhancing the magnetic anisotropy of the individual phases.
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75.75.Lf Electronic structure of magnetic nanoparticles
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A tunable spin filter in periodic diluted magnetic semiconductor/semiconductor superlattices

Yong Guo, Fei-Ruo Shen, and Xin-Yi Chen

Appl. Phys. Lett. 101, 012410 (2012); http://dx.doi.org/10.1063/1.4733668 (4 pages)

Online Publication Date: 6 July 2012

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We propose a tunable spin filter based on periodic diluted magnetic semiconductor/semiconductor (DMS/S) superlattices. It is found that periodic DMS/S superlattices can filter high efficiently not only spin-up electrons but also spin-down ones over a broad range of incident energies. The positions and widths of spin-filtering bands can be manipulated by adjusting the parameters of the superlattices or the external magnetic field. It is also found that the defect layer within the system generally leads to a strong suppression of spin-dependent transmission and makes the superlattices filter single-energy electrons. The results obtained may lead to potential applications in the field of spintronics.
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85.35.Gv Single electron devices
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High, magnetic field independent critical currents in (Ba,K)Fe2As2 crystals

L. Fang, Y. Jia, C. Chaparro, G. Sheet, H. Claus, M. A. Kirk, A. E. Koshelev, U. Welp, G. W. Crabtree, W. K. Kwok, S. Zhu, H. F. Hu, J. M. Zuo, H.-H. Wen, and B. Shen

Appl. Phys. Lett. 101, 012601 (2012); http://dx.doi.org/10.1063/1.4731204 (5 pages) | Cited 2 times

Online Publication Date: 2 July 2012

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Each discovery of a new high temperature superconductor drives the expectation that advanced engineering of materials defect structures will enable effective vortex pinning and high values of the electrical current density. Here, we demonstrate that single crystals of the iron-based superconductor Ba0.6K0.4Fe2As2 with Tc = 37.5 K can accommodate an unprecedented large concentration of strong-pinning defects in the form of discontinuous nm-sized nanorods with no degradation of the superconducting transition temperature. At a temperature of 5 K, we find a critical current density of 5 MA/cm2 that is magnetic field independent in fields up to 7 T.
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74.25.Sv Critical currents
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
74.62.-c Transition temperature variations, phase diagrams
74.70.Xa Pnictides and chalcogenides
74.25.F- Transport properties
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Piezoresponse properties of orderly assemblies of BaTiO3 and SrTiO3 nanocube single crystals

K. Mimura, K. Kato, H. Imai, S. Wada, H. Haneda, and M. Kuwabara

Appl. Phys. Lett. 101, 012901 (2012); http://dx.doi.org/10.1063/1.4731198 (4 pages) | Cited 2 times

Online Publication Date: 2 July 2012

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Orderly assemblies of BaTiO3 (BT) nanocubes, SrTiO3 (ST) nanocubes and BT-ST mixture nanocubes were fabricated on Pt-coated Si substrate directly by solution self-assembly and heated at 850 °C. The dielectric nanocubes aligned face to face in a quite wide region of several tens of square-micrometers with a height of one micrometer, and even inside of the structures was ordered. The piezoresponse of BT-ST mixture assembly showed non-linear curve and stepwise behavior at high poling field, which differed from ferroelectric BT and paraelectric ST nanocube assemblies.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
81.16.Dn Self-assembly
61.46.Hk Nanocrystals
77.80.-e Ferroelectricity and antiferroelectricity

Enhanced piezoelectric properties of (Na0.5+y+zK0.5−y)(Nb1−xTax)O3 ceramics

Y. S. Sung, S. Baik, J. H. Lee, G. H. Ryu, D. Do, T. K. Song, M. H. Kim, and W. J. Kim

Appl. Phys. Lett. 101, 012902 (2012); http://dx.doi.org/10.1063/1.4732523 (4 pages) | Cited 4 times

Online Publication Date: 2 July 2012

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A- and B-site ratios in (Na0.5+y+zK0.5−y)(Nb1−xTax)O3 ceramics with ABO3 structure were investigated to differentiate the effects of polymorphic phase transition (PPT), morphotropic phase boundary (MPB), and Na nonstoichiometry on piezoelectric coefficient (d33). MPB was intrinsically determined by the ratio between Na and K, whereas PPT was extrinsically controlled by Ta substitution. PPT temperature between orthorhombic and tetragonal phases (TO−T) was reduced to room temperature at x = 0.45. d33 was increased to 310 pC/N at y = 0.03 and z = 0 by the combined effects of PPT and MPB and was further enhanced to 333 pC/N by the Na nonstoichiometry at z = 0.015 with improved density.
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77.84.Ek Niobates and tantalates
61.66.Bi Elemental solids
61.66.Dk Alloys
77.65.-j Piezoelectricity and electromechanical effects
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Enhanced high thermal conductivity and low permittivity of polyimide based composites by core-shell Ag@SiO2 nanoparticle fillers

Yongcun Zhou, Lu Wang, Hu Zhang, Yuanyuan Bai, Yujuan Niu, and Hong Wang

Appl. Phys. Lett. 101, 012903 (2012); http://dx.doi.org/10.1063/1.4733324 (4 pages) | Cited 1 time

Online Publication Date: 2 July 2012

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A kind of polymer based composites was prepared by embedding the fillers of core-shell Ag@SiO2 nanoparticles into the polyimide (PI) matrix. The obtained Ag@SiO2/PI (50% vf of fillers) composites show remarkably improved high thermal conductivity and low relative permittivity. The maximum value of the thermal conductivity of composites is 7.88 W/(mK) and the relative permittivity and dielectric loss are about 11.7 and 0.015 at 1 MHz, respectively. Compared with self-passivated nanometer Al* particles composites, core-shell Ag@SiO2 nano-composite is beneficial to increase the thermal conductivity and reduce the permittivity of the composites. The relative mechanism was studied and discussed.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
77.22.Ch Permittivity (dielectric function)
81.05.Qk Reinforced polymers and polymer-based composites

Material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties produced using multi-wall carbon nanotubes wrapped with poly(ether sulphone) in a poly(ether ether ketone) matrix

Shuling Zhang, Hongsong Wang, Guibin Wang, and Zhenhua Jiang

Appl. Phys. Lett. 101, 012904 (2012); http://dx.doi.org/10.1063/1.4733723 (4 pages) | Cited 2 times

Online Publication Date: 2 July 2012

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A material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties was produced using multi-wall carbon nanotubes (MWCNTs) wrapped with poly(ether sulphone) (PES) dispersed in a poly(ether ether ketone) (PEEK) matrix. The material was fabricated using melt-blending, and MWCNT/PEEK composites show different degrees of improvement in the measured dielectric, mechanical, and thermal properties as compared to pure PEEK. This is attributed to the high conductivity of MWCNTs, the effect of wrapping MWCNTs with PES, the good dispersion of the wrapped MWCNTs in PEEK, and the strong interfacial adhesion between the wrapped MWCNTs and the PEEK.
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81.05.Qk Reinforced polymers and polymer-based composites
81.40.Lm Deformation, plasticity, and creep
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
82.35.Gh Polymers on surfaces; adhesion
68.35.Np Adhesion

Impedance spectroscopy of the superprotonic conduction in LiH2PO4

Jin Jung Kweon, Kyu Won Lee, Cheol Eui Lee, Kwang-Sei Lee, and Y. J. Jo

Appl. Phys. Lett. 101, 012905 (2012); http://dx.doi.org/10.1063/1.4732790 (3 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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Superprotonic conduction in the LiH2PO4 (LDP) system has been studied by means of impedance spectroscopy. A dielectric dispersion associated with room-temperature superionic conduction is manifested, as the temperature-dependent dielectric constant displays a broad peak shifting toward the high temperatures with increasing measuring frequency. In particular, our impedance spectroscopic analysis in distinct temperature ranges has revealed the evolution of the microscopic proton dynamics and inhomogeneous electric environments associated with the dynamics of the two distinct hydrogen-bond types in LDP.
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82.47.Aa Lithium-ion batteries
77.22.Ch Permittivity (dielectric function)
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