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8 Aug 2011

Volume 99, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 063701 (2011); http://dx.doi.org/10.1063/1.3622631 (3 pages)

Bomi Gweon, Mina Kim, Dan Bee Kim, Daeyeon Kim, Hyeonyu Kim, Heesoo Jung, Jennifer H. Shin, and Wonho Choe
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Efficiency enhancement of a-Si:H single junction solar cells by a-Ge:H incorporation at the p+ a-SiC:H/transparent conducting oxide interface

Jeehwan Kim, Ahmed I. Abou-Kandil, Augustin J. Hong, Mohamed M. Saad, Devendra K. Sadana, and Tze-Chiang Chen

Appl. Phys. Lett. 99, 062102 (2011); http://dx.doi.org/10.1063/1.3619185 (3 pages) | Cited 3 times

Online Publication Date: 8 August 2011

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Carbon (C) incorporation in the p+ hydrogenated amorphous silicon (a-SiC:H) is highly desirable for a-Si:H based solar cells because of the following reasons: (i) it increases the band gap of the p+ layer to ∼2 eV, which allows a majority of the sun light to pass through the thin p+ layer (∼15 nm) and get absorbed in the underlying intrinsic a-Si:H layer, and (ii) it enhances built-in potential of the a-Si:H p-i-n stack, resulting in enhanced short circuit current (JSC) and open circuit voltage (VOC). Hence, it is a desire to incorporate the highest possible C % in the p+ a-Si:H. However, C incorporation results in a Schottky barrier at the p+ a-SiC:H/transparent conducting oxide (TCO) interface, which degrades the fill factor (FF) of the solar cell. In this paper, we present a method that increases the C incorporation in p+ a-SiC:H but without adversely affecting the FF, by adding a thin layer of hydrogenated amorphous germanium (a-Ge:H) buffer at the p+ a-SiC:H/TCO interface. The presence of a-Ge:H can either minimize or eliminate the Schottky barrier. We demonstrate ∼25% enhanced efficiency of the a-Si:H solar cell by using the a-Ge:H interfacial buffer compared to that without an a-Ge:H interfacial layer.
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88.40.H- Solar cells (photovoltaics)

Impact of a few dopant positions controlled by deterministic single-ion doping on the transconductance of field-effect transistors

Masahiro Hori, Takahiro Shinada, Yukinori Ono, Akira Komatsubara, Kuninori Kumagai, Takashi Tanii, Tetsuo Endoh, and Iwao Ohdomari

Appl. Phys. Lett. 99, 062103 (2011); http://dx.doi.org/10.1063/1.3622141 (3 pages) | Cited 4 times

Online Publication Date: 8 August 2011

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As semiconductor device dimensions decrease, the individual impurity atom position becomes a critical factor in determining device performance. We fabricated transistors with ordered and random dopant distributions on one side of the channel and evaluated the transconductance to investigate the impact of discrete dopant positions on the electron transport properties. The largest transconductance was observed when dopants were placed on the drain side in an ordered distribution; this was attributed to the suppression of injection velocity degradation on the source side and the uniformity of the electrostatic potential. Thus, the control of discrete dopant positions could enhance the device performance.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Optical properties of high quality Cu2ZnSnSe4 thin films

F. Luckert, D. I. Hamilton, M. V. Yakushev, N. S. Beattie, G. Zoppi, M. Moynihan, I. Forbes, A. V. Karotki, A. V. Mudryi, M. Grossberg, J. Krustok, and R. W. Martin

Appl. Phys. Lett. 99, 062104 (2011); http://dx.doi.org/10.1063/1.3624827 (3 pages) | Cited 9 times

Online Publication Date: 9 August 2011

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Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectra.
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78.66.Li Other semiconductors
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Sensitivity improvement of silicon-on-insulator photodiode by gold nanoparticles with substrate bias control

Atsushi Ono, Yuki Matsuo, Hiroaki Satoh, and Hiroshi Inokawa

Appl. Phys. Lett. 99, 062105 (2011); http://dx.doi.org/10.1063/1.3622650 (3 pages)

Online Publication Date: 9 August 2011

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The sensitivity of silicon-on-insulator (SOI) lateral p-n junction photodiode was enhanced by attaching gold (Au) nanoparticles. This was confirmed by comparing I-V characteristics with and without Au nanoparticles at various substrate voltages. Twofold enhancement was attained in the visible wavelength region when the substrate was biased to positive. The substrate bias changed the area of depletion layer in SOI, and the light scattering by Au nanoparticles effectively enhanced the sensitivity when the area of depletion layer was small.
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85.60.Dw Photodiodes; phototransistors; photoresistors
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Measurement, analysis, and modeling of 1/f noise in pentacene thin film transistors

Hongki Kang, Lakshmi Jagannathan, and Vivek Subramanian

Appl. Phys. Lett. 99, 062106 (2011); http://dx.doi.org/10.1063/1.3622651 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2011

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In order to facilitate accurate noise modeling of organic thin-film-transistors (OTFTs), we provide comprehensive experimental results and analysis of unique low frequency noise characteristics in OTFTs. We conduct drain current noise measurements for pentacene-based thin-film-transistors (TFTs) having different grain size and operating region and use the resulting data to provide detailed mechanistic understanding of the underlying noise-generation phenomena that exist in OTFTs. The results show carrier trapping by traps within the semiconductor is the dominant source of low frequency noise and can be used in conjunction with a conventional unified noise model to accurately describe the noise behavior of pentacene TFTs.
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85.30.Tv Field effect devices
05.40.Ca Noise
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Structural and semiconductor-to-metal transitions of double-perovskite cobalt oxide Sr2−xLaxCoTiO6−δ with enhanced thermoelectric capability

Tohru Sugahara and Michitaka Ohtaki

Appl. Phys. Lett. 99, 062107 (2011); http://dx.doi.org/10.1063/1.3623476 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2011

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The thermoelectric properties of double-perovskite oxide Sr2−xLaxCoTiO6−δ were revealed to vary anomalously with the La concentration, plausibly due to a structural transition found in this study. Although the temperature dependence of the resistivity and thermopower of the present oxide showed a semiconductor-to-metal transition similar to those observed for other perovskite-related Co oxides such as Sr1−xYxCoO3−δ, the transition temperature was more than 350 K higher, implying considerable stabilization of the low-spin state of Co ions in the double-perovskite oxide. Consequently, the operating temperature range of the oxide for potential thermoelectric applications was significantly expanded toward higher temperatures.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.20.Pa Thermoelectric and thermomagnetic effects
72.60.+g Mixed conductivity and conductivity transitions

Origin of threshold voltage shift by interfacial trap density in amorphous InGaZnO thin film transistor under temperature induced stress

Bosul Kim, Eugene Chong, Do Hyung Kim, Yong Woo Jeon, Dae Hwan Kim, and Sang Yeol Lee

Appl. Phys. Lett. 99, 062108 (2011); http://dx.doi.org/10.1063/1.3615304 (3 pages) | Cited 4 times

Online Publication Date: 9 August 2011

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Effect of trap-density of amorphous InGaZnO thin film transistors (a-IGZO TFTs) were studied using different analysis of x-ray photoelectron spectroscopy (XPS) depth profile and density of states (DOSs). To change trap-densities systematically, rf-power was varied to cause different effect on the initial growth stage of a-IGZO layer grown on gate insulator. The interfacial trap-density was confirmed to be dominant effect on the performance and the threshold voltage shift of a-IGZO TFT by observing the variation of O1s binding energy from XPS. The relation between temperature stress induced and trap-density in deep level was investigated by analyzing DOSs.
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85.30.Tv Field effect devices

Correlation between low-frequency current-noise enhancement and high-frequency oscillations in GaN-based planar nanodiodes: A Monte Carlo study

A. Íñiguez-de-la-Torre, I. Íñiguez-de-la-Torre, J. Mateos, and T. González

Appl. Phys. Lett. 99, 062109 (2011); http://dx.doi.org/10.1063/1.3613956 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2011

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We present a spectral analysis of time sequences of current, calculated by means of Monte Carlo simulations, in GaN-based asymmetric nanodiodes, devices that are potential candidates to exhibit Gunn oscillations. It is found that the low-frequency noise increases significantly for biases close to the threshold voltage of Gunn oscillations, taking place at much higher frequencies of hundreds of gigahertz. Due to the inherent difficulty in detecting so fast fluctuations, the measurement of the low-frequency noise can be a quite useful tool for predicting current oscillations at sub-terahertz frequencies in these devices.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

High rate dry etching of InGaZnO by BCl3/O2 plasma

Wanjae Park, Ki-Woong Whang, Young Gwang Yoon, Jeong Hwan Kim, Sang-Ho Rha, and Cheol Seong Hwang

Appl. Phys. Lett. 99, 062110 (2011); http://dx.doi.org/10.1063/1.3624594 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2011

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This paper reports the results of the high-rate dry etching of indium gallium zinc oxide (IGZO) at room temperature using BCl3/O2 plasma. We achieved an etch rate of 250 nm/min. We inferred from the x-ray photoelectron spectroscopy analysis that BOx or BOClx radicals generated from BCl3/O2 plasma cause the etching of the IGZO material. O2 initiates the etching of IGZO, and Ar removes nonvolatile byproducts from the surface during the etching process. Consequently, a smooth etched surface results when these gases are added to the etch gas.
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81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Two-dimensional deformation potential model of mobility in small molecule organic semiconductors

J. E. Northrup

Appl. Phys. Lett. 99, 062111 (2011); http://dx.doi.org/10.1063/1.3624588 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2011

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An acoustic deformation potential model appropriate for transport in two dimensions is employed to estimate upper limits on the intrinsic hole mobility of DNTT-C10 [2,9-dialkyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene] and BTBT-C12 [2,7-dialkyl[1]benzo-thieno[3,2-b][1]benzothiophene]. First-principles calculations are employed to determine the values of effective masses, deformation potentials, and elastic constants entering the model. The analysis suggests that the upper limit on room temperature mobility within a single crystalline region in DNTT-C10 or BTBT-C12 may be some tens of cm2/Vs. The width of the π-bonded molecular core in the direction perpendicular to the transport plane is identified as a structural feature affecting mobility in two-dimensional organic semiconductors.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
71.15.-m Methods of electronic structure calculations
71.20.Rv Polymers and organic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
81.40.Jj Elasticity and anelasticity, stress-strain relations

Enhanced thermoelectric power factor with impurity-induced resonant level

M. Liu, X. Y. Qin, C. S. Liu, and Z. Zeng

Appl. Phys. Lett. 99, 062112 (2011); http://dx.doi.org/10.1063/1.3624467 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2011

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Based on the resonant level concept, we presented an analytic calculation for the enhancement of the thermoelectric properties of semiconductor materials with element doping. We show that the power factor can be significantly enhanced due to a resonant energy level introduced by some element lies in the host bands and near the Fermi level and band edge. Our calculations reveal that by choosing optimal parameters for the element doping, such as impurity level, and doping concentration, one can obtain an optimum power factor for improved thermoelectric performance.
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71.55.Ht Other nonmetals
72.20.Pa Thermoelectric and thermomagnetic effects
73.20.At Surface states, band structure, electron density of states
73.20.Fz Weak or Anderson localization
61.72.up Other materials

Link between crystal quality and electrical properties of metalorganic vapour phase epitaxy InxGa1−xN thin films

V. Gorge, Z. Djebbour, A. Migan-Dubois, C. Pareige, C. Longeaud, K. Pantzas, T. Moudakir, S. Gautier, G. Orsal, P. L. Voss, and A. Ougazzaden

Appl. Phys. Lett. 99, 062113 (2011); http://dx.doi.org/10.1063/1.3624598 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2011

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We report on the crystal quality of metalorganic vapour phase epitaxy-grown InGaN with indium content ranging from 0% to 20%. Absorbance measurements are fit to a model including band tails and a defect represented as a Brendel oscillator (R. Brendel, Appl. Phys. A 50, 587, 1990). Band tail absorbance, corresponding to contorted bonds, increases with increased In content. Above 10% of In, the presence of another defect, the concentration of which increases with In content, has been correlated with x-ray diffraction and Raman. We suggest that this defect corresponds to nitrogen vacancies, in agreement with a reported model for GaN.
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68.55.ag Semiconductors
78.30.Fs III-V and II-VI semiconductors
61.72.jd Vacancies
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Field-effect modulation of conductance in VO2 nanobeam transistors with HfO2 as the gate dielectric

Shamashis Sengupta, Kevin Wang, Kai Liu, Ajay K. Bhat, Sajal Dhara, Junqiao Wu, and Mandar M. Deshmukh

Appl. Phys. Lett. 99, 062114 (2011); http://dx.doi.org/10.1063/1.3624896 (3 pages) | Cited 7 times

Online Publication Date: 12 August 2011

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We study field-effect transistors realized from VO2 nanobeams with HfO2 as the gate dielectric. When heated up from low to high temperatures, VO2 undergoes an insulator-to-metal transition. We observe a change in conductance (∼6%) of our devices induced by gate voltage when the system is in the insulating phase. The response is reversible and hysteretic, and the area of hysteresis loop becomes larger as the rate of gate sweep is slowed down. A phase lag exists between the response of the conductance and the gate voltage. This indicates the existence of a memory of the system and we discuss its possible origins.
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72.60.+g Mixed conductivity and conductivity transitions
77.80.Dj Domain structure; hysteresis
85.30.Tv Field effect devices
71.30.+h Metal-insulator transitions and other electronic transitions
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Magnetic signature of symmetry reduction in epitaxial La0.67Sr0.33MnO3 films

Radhika Barua, L. H. Lewis, and D. Heiman

Appl. Phys. Lett. 99, 062501 (2011); http://dx.doi.org/10.1063/1.3623442 (3 pages)

Online Publication Date: 8 August 2011

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The magnetic properties of epitaxially grown La0.67Sr0.33MnO3 perovskite thin films were investigated to elucidate an unexpected broken symmetry between orthogonal [100] and [010] inplane directions, resulting from the magnetostructural coupling between the film and the cubic SrTiO3 (001) substrate. The films were synthesized by molecular beam epitaxy with either complete or zero A-site cation disorder. Magnetization measured in [100] and [010] directions shows differences that signal a reduction of the in-plane cubic symmetry only for T < 290 K. The magnetization asymmetry is more robust in the film with complete A-site disorder. These results are attributed to a dominant Mn3+ character at the film-substrate interface and an associated out-of-plane bonding character with hypothesized origins in both charge imbalance and strain effects.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.at Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Origin of magnetic switching field distribution in bit patterned media based on pre-patterned substrates

B. Pfau, C. M. Günther, E. Guehrs, T. Hauet, H. Yang, L. Vinh, X. Xu, D. Yaney, R. Rick, S. Eisebitt, and O. Hellwig

Appl. Phys. Lett. 99, 062502 (2011); http://dx.doi.org/10.1063/1.3623488 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2011

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Using a combination of synchrotron radiation based magnetic imaging and high-resolution transmission electron microscopy we reveal systematic correlations between the magnetic switching field and the internal nanoscale structure of individual islands in bit patterned media fabricated by Co/Pd-multilayer deposition onto pre-patterned substrates. We find that misaligned grains at the island periphery are a common feature independent of the island switching field, while irregular island shapes and misaligned grains specifically extending into the center of an island are systematically correlated with a reduced island reversal field.
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81.05.Bx Metals, semimetals, and alloys
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.50.Ss Magnetic recording materials
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetism of covalently functionalized carbon nanotubes

Elton J. G. Santos, D. Sánchez-Portal, and A. Ayuela

Appl. Phys. Lett. 99, 062503 (2011); http://dx.doi.org/10.1063/1.3623755 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2011

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We investigate the electronic structure of carbon nanotubes functionalized by adsorbates anchored with single C-C covalent bonds. We find that despite the particular adsorbate, a spin moment with a universal value of 1.0 μB per molecule is induced at low coverage. Therefore, we propose a mechanism of bonding-induced magnetism at the carbon surface. The adsorption of a single molecule creates a dispersionless defect state at the Fermi energy, which is mainly localized in the carbon wall and presents a small contribution from the adsorbate. This universal spin moment is fairly independent of the coverage as long as all the molecules occupy the same graphenic sublattice. The magnetic coupling between adsorbates is also studied and reveals a key dependence on the graphenic sublattice adsorption site.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.20.Tx Fullerenes and related materials; intercalation compounds
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Electric control of magnon frequencies and magnetic moment of bismuth ferrite thin films at room temperature

Ashok Kumar, J. F. Scott, and R. S. Katiyar

Appl. Phys. Lett. 99, 062504 (2011); http://dx.doi.org/10.1063/1.3624845 (3 pages) | Cited 8 times

Online Publication Date: 10 August 2011

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Here, we report the tuning of room-temperature magnon frequencies from 473 GHz to 402 GHz (14%) and magnetic moment from 4 to 18 emu/cm3 at 100 Oe under the application of external electric fields (E) across interdigital electrodes in BiFeO3 (BFO) thin films. A decrease in magnon frequencies and increase in phonon frequencies were observed with Magnon and phonon Raman intensities are asymmetric with polarity, decreasing with positive E (+E) and increasing with negative E (−E) where polarity is with respect to in-plane polarization P. The magnetoelectric coupling (α) is proved to be linear and a rather isotropic α = 8.5 × 10−12 sm−1.
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75.85.+t Magnetoelectric effects, multiferroics
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films

Contribution of the easy axis orientation, anisotropy distribution and dot size on the switching field distribution of bit patterned media

Jehyun Lee, Christoph Brombacher, Josef Fidler, Barbara Dymerska, Dieter Suess, and Manfred Albrecht

Appl. Phys. Lett. 99, 062505 (2011); http://dx.doi.org/10.1063/1.3623752 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2011

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A magnetic nanostructure array was fabricated by post-patterning of a L10 ordered 5-nm-thick FePtCu film revealing a rather broad switching field distribution (SFD). The individual contributions to the SFD of the dot array were investigated by micromagnetic simulations. Based on transmission electron microscopy results, the dots show a truncated cone shape which was directly used for the finite element model. The influence of single parameters, i.e., easy axis distribution, magnetic anisotropy, and dot size, on the SFD was estimated quantitatively and compared. Furthermore, the influence of damage induced during the nanofabrication process was analyzed and correlated with experimental results.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.75.-c Magnetic properties of nanostructures
02.70.Dh Finite-element and Galerkin methods
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.-d Domain effects, magnetization curves, and hysteresis

Effect of interparticle interactions and size dispersion in magnetic nanoparticle assemblies: A static and dynamic study

Ji Sung Lee, Reasmey P. Tan, Jun Hua Wu, and Young Keun Kim

Appl. Phys. Lett. 99, 062506 (2011); http://dx.doi.org/10.1063/1.3624833 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2011

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Interparticle interactions in magnetic nanoparticles are studied by dc and ac magnetization measurements. For non-interacting nanoparticles, while the anisotropy constant of the nanoparticles Keff = 1.6 × 105 erg/cm3 is accurately determined by fitting zero-field-cooled and field-cooled measurements, we show that Keff values deduced only from time relaxation measurements must require simultaneous adjustments of the complex susceptibility by taking into account the size distribution of nanoparticles. This leads to Keff = 1.7 × 105 erg/cm3 in agreement with dc measurements. For interacting nanoparticles, comparisons with theoretical models show that energies due to magnetic dipolar interactions can only be predicted for weak and moderate interactions.
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75.75.Jn Dynamics of magnetic nanoparticles
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.78.-n Magnetization dynamics

Competitive roles of elastic and magnetic interactions in twin boundary behaviors of magnetic shape memory alloys

Yongmei M. Jin

Appl. Phys. Lett. 99, 062507 (2011); http://dx.doi.org/10.1063/1.3625428 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2011

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Domain microstructure evolutions under applied magnetic field in magnetic shape memory alloys are investigated by phase field micromagnetic microelastic modeling. The computer simulations reveal respective roles of elastic interaction, magnetic interaction, and their competition in the coupled magnetic and elastic domain processes. It is observed that different relative strengths of elastic interaction with respect to magnetic interaction lead to different domain evolution pathways and different twin boundary behaviors, including field-induced twin boundary displacement, deformation, and annihilation. Distinct twin boundary behaviors driven by magnetic field from that driven by mechanical stress are discussed.
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81.40.Lm Deformation, plasticity, and creep
62.20.dq Other elastic constants
62.20.fg Shape-memory effect; yield stress; superelasticity
75.60.Ch Domain walls and domain structure
81.40.Jj Elasticity and anelasticity, stress-strain relations

Control of spin configuration in half-metallic La0.7Sr0.3MnO3 nano-structures

J. Rhensius, C. A. F. Vaz, A. Bisig, S. Schweitzer, J. Heidler, H. S. Körner, A. Locatelli, M. A. Niño, M. Weigand, L. Méchin, F. Gaucher, E. Goering, L. J. Heyderman, and M. Kläui

Appl. Phys. Lett. 99, 062508 (2011); http://dx.doi.org/10.1063/1.3623480 (3 pages) | Cited 7 times

Online Publication Date: 11 August 2011

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We investigate the interplay between the governing magnetic energy terms in patterned La0.7Sr0.3MnO3 (LSMO) elements by direct high-resolution x-ray magnetic microscopy as a function of temperature and geometrical parameters. We show that the magnetic configurations evolve from multidomain to flux-closure states (favored by the shape anisotropy) with decreasing element size, with a thickness-dependent crossover at the micrometer scale. The flux-closure states are stable against thermal excitations up to near the Curie temperature. Our results demonstrate control of the spin state in LSMO elements by judicious choice of the geometry, which is key for spintronics applications requiring high spin-polarizations and robust magnetic states.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Wx Spin crossover
75.60.Ch Domain walls and domain structure

Substrate-dependent quasiparticle recombination time in superconducting resonators

N. Vercruyssen, R. Barends, T. M. Klapwijk, J. T. Muhonen, M. Meschke, and J. P. Pekola

Appl. Phys. Lett. 99, 062509 (2011); http://dx.doi.org/10.1063/1.3624463 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2011

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We demonstrate an increased quasiparticle recombination time in superconducting resonators on a SiNx membrane, compared to identical resonators on a SiNx/Si wafer. An interpretation is given using a thermal model of the membrane. Using an array of tunnel junctions to cool or heat the membrane, we show that the resonators on the membranes are extremely sensitive to small changes of the phonon temperature, which renders them excellent phonon thermometers with a noise level equivalent to 5μK/math. The experimental set-up is in principle an ideal platform to study the interplay of quasiparticles and phonon populations in superconductors.
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85.25.Cp Josephson devices

Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions with low critical current density

Luigi Longobardi, Davide Massarotti, Giacomo Rotoli, Daniela Stornaiuolo, Gianpaolo Papari, Akira Kawakami, Giovanni Piero Pepe, Antonio Barone, and Francesco Tafuri

Appl. Phys. Lett. 99, 062510 (2011); http://dx.doi.org/10.1063/1.3624471 (3 pages) | Cited 6 times

Online Publication Date: 11 August 2011

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High quality epitaxial NbN/MgO/NbN Josephson junctions have been realized with MgO barriers up to a thickness of d = 1 nm. The junction properties coherently scale with the size of barrier, and low critical current densities down to 3 A/cm2 have been achieved for larger barriers. In this limit, junctions exhibit macroscopic quantum phenomena for temperatures lower than 90 mK. Measurements and junction parameters support the notion of a possible use of these devices for multiphoton quantum experiments, taking advantage of the fast non equilibrium electron-phonon relaxation times of NbN.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.25.Kc Phonons
74.25.Sv Critical currents

Low frequency noise due to magnetic inhomogeneities in submicron FeCoB/MgO/FeCoB magnetic tunnel junctions

D. Herranz, A. Gomez-Ibarlucea, M. Schäfers, A. Lara, G. Reiss, and F. G. Aliev

Appl. Phys. Lett. 99, 062511 (2011); http://dx.doi.org/10.1063/1.3615798 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2011

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We report on room temperature low frequency noise due to magnetic inhomogeneities/domain walls (MI/DWs) in elliptic submicron FeCoB/MgO/FeCoB magnetic tunnel junctions with an area between 0.0245 and 0.0675 μm2. In the smaller area junctions we found an unexpected random telegraph noise (RTN1), deeply in the parallel state, possibly due to stray field induced MI/DWs in the hard layer. The second noise source (RTN2) is observed in the antiparallel state for the largest junctions. Strong asymmetry of RTN2 and of related resistance steps with current indicate spin torque acting on the MI/DWs in the soft layer at current densities below 5 × 105 A/cm2.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure

On the role of Al doping in La0.7Ca0.3MnO3: A magnetic Compton scattering study

B. L. Ahuja, Shailja Tiwari, Alpa Dashora, H. S. Mund, Jagrati Sahariya, D. M. Phase, R. J. Choudhary, A. Banerjee, M. Itou, and Y. Sakurai

Appl. Phys. Lett. 99, 062512 (2011); http://dx.doi.org/10.1063/1.3624843 (3 pages) | Cited 2 times

Online Publication Date: 12 August 2011

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Spin and orbital magnetic moments in hole doped manganite La0.7Ca0.3Mn1−xAlxO3 (x = 0, 0.02, and 0.06) have been scrutinized using experimental spin momentum densities. An analysis of magnetic Compton profiles shows that the spin moment of Mn 3d has a major contribution towards the total spin moment and its contribution decreases as we increase the concentration of Al. The present experiment along with magnetization data predict orbital moment of −0.29 ± 0.03 μB/f.u. in the parent compound (x = 0), which almost disappears on substitution of Al. The results are explained on the basis of imbalance in Mn3+ and Mn4+ charge ratio in these compounds.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.-g Interactions of particles and radiation with matter
61.72.U- Doping and impurity implantation
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