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6 Aug 2012

Volume 101, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages)

Mahdi Jamali, Kulothungasagaran Narayanapillai, Jae Hyun Kwon, and Hyunsoo Yang
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Observation of liquid crystals confined in an elliptic cylinder

Joonwoo Jeong and Mahn Won Kim

Appl. Phys. Lett. 101, 061914 (2012); http://dx.doi.org/10.1063/1.4745773 (4 pages) | Cited 1 time

Online Publication Date: 9 August 2012

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We present the observation of liquid crystals confined in elliptic cylinders. To fabricate the elliptic cylinder, poly(dimethlysiloxane) micro-channels having circular cross sections are stretched uniaxially along the direction of the diameter. Upon increasing the aspect ratio of the elliptic cross section, confined nematic liquid crystals maintain their escaped-radial configuration with homeotropic anchoring. In smectic-A liquid crystals, defect regions of focal conic domains appear as a function of the aspect ratio. We propose a model to understand the formation of these defects in terms of the confinement-induced misorientation, and resultant tilt grain boundaries.
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61.30.Jf Defects in liquid crystals

Photoluminescence studies of type-II CdSe/CdTe superlattices

Jing-Jing Li, Leijun Yin, Shane R. Johnson, B. J. Skromme, Shumin Wang, Xinyu Liu, Ding Ding, Cun-Zheng Ning, Jacek K. Furdyna, and Yong-Hang Zhang

Appl. Phys. Lett. 101, 061915 (2012); http://dx.doi.org/10.1063/1.4745199 (4 pages)

Online Publication Date: 9 August 2012

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CdSe/CdTe type-II superlattices grown on GaSb substrates by molecular beam epitaxy are studied using time-resolved and steady-state photoluminescence (PL) spectroscopy at 10 K. The relatively long carrier lifetime of 188 ns observed in time-resolved PL measurements shows good material quality. The steady-state PL peak position exhibits a blue shift with increasing excess carrier concentration. Self-consistent solutions of the Schrödinger and Poisson equations show that this effect can be explained by band bending as a result of the spatial separation of electrons and holes, which is critical confirmation of a strong type-II band edge alignment between CdSe and CdTe.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.47.jd Time resolved luminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Et II-VI semiconductors

Controllable acoustic media having anisotropic mass density and tunable speed of sound

Mark J. Seitel, Jerry W. Shan, and Stephen D. Tse

Appl. Phys. Lett. 101, 061916 (2012); http://dx.doi.org/10.1063/1.4742927 (4 pages)

Online Publication Date: 10 August 2012

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We present an experimental demonstration of a reconfigurable acoustic metafluid having anisotropic, actively controllable speed of sound for ultrasonic waves. The acoustic metamaterial is based upon suspensions of subwavelength discoid particles whose orientation and interparticle interactions are manipulated by external magnetic fields. Measured sound speeds are direction- and frequency-dependent, changing in a nonlinear fashion with particle concentration when an external magnetic field is applied. The observed changes in sound speed are significantly greater than that expected for suspensions of oriented but non-interacting oblate-spheroidal particles, suggesting that interactions between particles are important even for particle volume fractions below 0.5%.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
51.40.+p Acoustical properties
62.60.+v Acoustical properties of liquids
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
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The zero temperature coefficient in junctionless nanowire transistors

Renan Doria Trevisoli, Rodrigo Trevisoli Doria, Michelly de Souza, Samaresh Das, Isabelle Ferain, and Marcelo Antonio Pavanello

Appl. Phys. Lett. 101, 062101 (2012); http://dx.doi.org/10.1063/1.4744965 (3 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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This Letter presents an analysis of the zero temperature coefficient (ZTC) bias in junctionless nanowire transistors (JNTs). Unlike in previous works, which had shown that JNT did not present a ZTC point, this work shows that ZTC may occur in JNTs depending mainly on the series resistance of the devices and its dependence on the temperature. Experimental results of drain current, threshold voltage, and series resistance are presented for both long and short channel n and p-type devices.
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85.30.Tv Field effect devices

Influence of indium cluster on the high and constant background electron density in ternary InxGa1−xN alloys

Chong Li, Fengmin Wu, Shu-Shen Li, Jian-Bai Xia, and Jingbo Li

Appl. Phys. Lett. 101, 062102 (2012); http://dx.doi.org/10.1063/1.4745008 (4 pages) | Cited 1 time

Online Publication Date: 7 August 2012

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First principles calculations and special quasirandom structure approach have been used to study the origin of the unintentional high and constant background electron density observed in InxGa1−xN alloys. Our results show that the formation energy of nitrogen vacancy (VN) surprisingly becomes nearly constant for alloys with relatively high In concentration. In strong contrast, the formation energy of hydrogenated nitrogen vacancy (HN) or interstitial hydrogen (Hi) monotonically decreases as x increases, indicating that neither HN nor Hi, but VN is the main sources of the experiment observed high and constant electron density in the alloys. The underlying mechanism is discussed.
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81.65.-b Surface treatments
82.30.-b Specific chemical reactions; reaction mechanisms
61.72.jd Vacancies

Brillouin scattering determination of the surface acoustic wave velocity in InxGa1−xN: A probe into the elastic constants

R. J. Jiménez-Riobóo, R. Cuscó, R. Oliva, N. Domènech-Amador, C. Prieto, J. Ibáñez, C. Boney, A. Bensaoula, and L. Artús

Appl. Phys. Lett. 101, 062103 (2012); http://dx.doi.org/10.1063/1.4744961 (4 pages)

Online Publication Date: 8 August 2012

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We have determined the surface acoustic wave velocity in InxGa1−xN layers for 0.34<x<0.75 by means of high resolution Brillouin spectroscopy. The sagittal dependence of the surface acoustic velocity has been analyzed by comparing the experimental results with theoretical simulations based on the Green’s function formalism. We find the best agreement with our data when the bowing parameters for the elastic constants recently reported from density functional theory calculations are taken into account. The dependence of the surface acoustic wave velocity on alloy composition is given.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.dq Other elastic constants
62.65.+k Acoustical properties of solids
68.35.Iv Acoustical properties

Monitoring structural influences on quantum transport in InAs nanowires

Robert Frielinghaus, Kilian Flöhr, Kamil Sladek, Thomas E. Weirich, Stefan Trellenkamp, Hilde Hardtdegen, Thomas Schäpers, Claus M. Schneider, and Carola Meyer

Appl. Phys. Lett. 101, 062104 (2012); http://dx.doi.org/10.1063/1.4742326 (4 pages) | Cited 1 time

Online Publication Date: 8 August 2012

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A sample design that allows for quantum transport and transmission electron microscopy (TEM) on individual suspended nanostructures is used to investigate moderately n-type doped InAs nanowires (NWs). The nanowires were grown by metal organic vapor phase epitaxy. Universal conductance fluctuations in the nanowires are investigated at temperatures down to 0.35 K. These fluctuations show two different temperature dependences. The very same nanowire segments investigated in transport are subsequently analyzed by TEM revealing crystal phase mixing. However, we find no correspondence between the atomic structure of the wires and the temperature dependences of the conductance fluctuations.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.55.A- Nucleation and growth
73.61.Ey III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.16.Dn Self-assembly

Optical and defect properties of hydrothermal ZnO with low lithium contamination

R. Heinhold, H.-S. Kim, F. Schmidt, H. von Wenckstern, M. Grundmann, R. J. Mendelsberg, R. J. Reeves, S. M. Durbin, and M. W. Allen

Appl. Phys. Lett. 101, 062105 (2012); http://dx.doi.org/10.1063/1.4739515 (5 pages)

Online Publication Date: 8 August 2012

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The removal of lithium and other group I contaminants from hydrothermally grown ZnO results in significant changes in its electrical, optical, and device characteristics. A significant reduction in donor compensation allows the fabrication of low series resistance Schottky contacts with extremely high rectification ratios and also quenches 4 K photoluminescence emission from excitons bound to ionized donors. Three new electron traps with activation energies of 115, 160, and 190 meV are created along with an increase in the activation energy of the dominant shallow donor from 50 to 70 eV which is associated with an accompanying removal of aluminum.
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78.55.Et II-VI semiconductors
85.30.Kk Junction diodes
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ei Rectification

Enhanced optical absorption and photocatalytic activity of anatase TiO2 through (Si,Ni) codoping

Yanming Lin, Zhenyi Jiang, Chaoyuan Zhu, Xiaoyun Hu, Xiaodong Zhang, Haiyan Zhu, and Jun Fan

Appl. Phys. Lett. 101, 062106 (2012); http://dx.doi.org/10.1063/1.4745193 (5 pages) | Cited 6 times

Online Publication Date: 9 August 2012

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The electronic and optical properties of (Si,Ni)-codoped anatase TiO2 are investigated using the density functional theory. The calculated results indicate that the synergistic effects of (Si,Ni) codoping can effectively extend the optical absorption edge, which can lead to higher visible-light photocatalytic activity than pure anatase TiO2. To verify the reliability of our calculated results, nanocrystalline (Si,Ni)-codoped TiO2 is synthesized by a sol-gel-solvothermal method, and experimental results also show that the (Si,Ni)-codoped sample exhibits better absorption performance and higher photocatalytic activities than pure TiO2.
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81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.40.Ha Other nonmetallic inorganics

“Smart” silicon: Switching between p‐ and n‐conduction under compression

Sergey V. Ovsyannikov, Igor V. Korobeinikov, Natalia V. Morozova, Andrzej Misiuk, Nikolai V. Abrosimov, and Vladimir V. Shchennikov

Appl. Phys. Lett. 101, 062107 (2012); http://dx.doi.org/10.1063/1.4742345 (4 pages) | Cited 3 times

Online Publication Date: 9 August 2012

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We report results of thermoelectric power (Seebeck effect) and Raman spectroscopy studies on undoped and Ge-doped (1.4–2.6 at. %) Czochralski-grown silicon under high pressure to ∼17 GPa. Lattice dynamics of Si:Ge under compression resembles that in Ge-free silicon. But in contrary to undoped silicon, the electrical conduction in Si1−xGex may be reversibly (irreversibly) “switched” from p- to n-type by application of pressure of ∼0.6 GPa (∼0.8–1.5 GPa). Under pressures higher than ∼2 GPa the samples turn to a compensated state. Thus, Si:Ge being a “smart” material that opens emergent perspectives for silicon-based devices. It may be utilized, e.g., as a “smart” substrate for integrated circuits or a “smart” layer in heterostructures.
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72.20.Pa Thermoelectric and thermomagnetic effects
78.30.Am Elemental semiconductors and insulators
81.10.Fq Growth from melts; zone melting and refining
62.50.-p High-pressure effects in solids and liquids

The CuInSe2–CuIn3Se5 defect compound interface: Electronic structure and band alignment

A. Hofmann and C. Pettenkofer

Appl. Phys. Lett. 101, 062108 (2012); http://dx.doi.org/10.1063/1.4739790 (4 pages)

Online Publication Date: 10 August 2012

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The interface formation between stoichiometric chalcopyrite CuInSe2 and the copper-deficient defect phase CuIn3Se5 is investigated by in situ photoelectron spectroscopy. The use of epitaxial samples allows for the preparation of highly defined surfaces and accurate analysis of the electronic structure. Valence band structures measured with synchrotron-based photoelectron spectroscopy are in agreement with density functional theory. We observe a lowering of the top valence band of CuIn3Se5 of 0.29 eV with respect to CuInSe2. The increased optical gap for copper-deficient material leads to aligned conduction bands.
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71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Li Other semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Carrier localization in InN/InGaN multiple-quantum wells with high In-content

S. Valdueza-Felip, L. Rigutti, F. B. Naranjo, P. Ruterana, J. Mangeney, F. H. Julien, M. González-Herráez, and E. Monroy

Appl. Phys. Lett. 101, 062109 (2012); http://dx.doi.org/10.1063/1.4742157 (4 pages)

Online Publication Date: 10 August 2012

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We study the carrier localization in InN/In0.9Ga0.1N multiple-quantum-wells (MQWs) and bulk InN by means of temperature-dependent photoluminescence and pump-probe measurements at 1.55 μm. The S-shaped thermal evolution of the emission energy of the InN film is attributed to carrier localization at structural defects with an average localization energy of ∼12 meV. Carrier localization is enhanced in the MQWs due to well/barrier thickness and ternary alloy composition fluctuations, leading to a localization energy above 35 meV and longer carrier relaxation time. As a result, the luminescence efficiency in the MQWs is improved by a factor of five over bulk InN.
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78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.07.St Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
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Detection of domain wall eigenfrequency in infinity-shaped magnetic nanostructures

Mahdi Jamali, Kulothungasagaran Narayanapillai, Jae Hyun Kwon, and Hyunsoo Yang

Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages)

Online Publication Date: 6 August 2012

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The dynamics of a magnetic infinity-shaped nanostructure has been experimentally studied by two different techniques such as the sinusoidal resonance excitation and the damped short pulse excitation to measure the eigenfrequency of domain walls. Direct observation of the magnetic domain wall nucleation has been measured in the frequency domain. Electrical measurements of the domain wall dynamics in the frequency domain reveal the existence of multi-eigenmodes for large excitation amplitudes. The time-resolved measurements show that the frequency of the damped gyration is similar to that of the frequency domain and indicate coexistence of spin wave excitations.
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75.60.Ch Domain walls and domain structure
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Ds Spin waves
02.10.Ud Linear algebra

Large half-metallic gap in ferromagnetic semi-Heusler alloys CoCrP and CoCrAs

Zhongyu Yao, Y. S. Zhang, and K. L. Yao

Appl. Phys. Lett. 101, 062402 (2012); http://dx.doi.org/10.1063/1.4742867 (4 pages)

Online Publication Date: 6 August 2012

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We investigate the electronic structure and magnetism of semi-Heusler alloys CoCrP and CoCrAs using the full-potential linearized augmented plane wave method. The calculations reveal that CoCrP and CoCrAs are half-metallic (HM) ferromagnets with the same magnetic moment of 2.00 μB per formula unit. Both alloys have large half-metallic gaps (up to 0.50 eV) and wide band gaps (above 1 eV). The half-metallicity of CoCrP and CoCrAs can be retained even when their lattice constants are changed by −4.8% to 6.6% and −7.7% to 4.5%, respectively. The two alloys show great promise in the applications of spin valve and magnetic tunnel junction.
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81.05.Bx Metals, semimetals, and alloys
61.66.Dk Alloys
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Be Transition metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys

Interband dephasing and photon echo response in GaMnAs

M. Yildirim, S. March, R. Mathew, A. Gamouras, X. Liu, M. Dobrowolska, J. K. Furdyna, and K. C. Hall

Appl. Phys. Lett. 101, 062403 (2012); http://dx.doi.org/10.1063/1.4742916 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Coherent carrier dynamics are studied in GaMnAs using time-integrated and time-resolved four-wave mixing techniques. Dephasing is observed to be dominated by spin-flip scattering between the optically injected holes and Mn ions, revealing the rapid time scale of this scattering process in the III-Mn-V diluted magnetic semiconductors. The optical response is shown to exhibit the characteristic signatures of a simple photon echo, despite the complexity of band tail contributions and strong exchange coupling in this system.
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78.47.jf Photon echoes
72.20.Fr Low-field transport and mobility; piezoresistance
75.50.Pp Magnetic semiconductors

Interlayer magnetostatic coupling and linear magnetoresistance in [Pd/Co]/MgO/Co junction sensor

C. Song, Y. Y. Wang, X. J. Li, G. Y. Wang, and F. Pan

Appl. Phys. Lett. 101, 062404 (2012); http://dx.doi.org/10.1063/1.4742999 (4 pages)

Online Publication Date: 6 August 2012

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We investigate interlayer magnetostatic coupling and linear magnetoresistance in [Pd/Co]/MgO/Co and [Pd/Co]/MgO/Co/MgO/[Co/Pd] tunnel junctions, where Co/Pd and Co ferromagnetic layers exhibit out-of-plane and in-plane magnetic anisotropy, respectively. Because of the magnetostatic interaction between Co moments and the stray field from Co/Pd stripe domains, the Co layer shows a significant enhancement of coercivity and exchange bias. Linear magnetoresistance is observed in both junctions in the field up to 15 kOe with the current perpendicular to the film plane, due to coherent rotation of the ferromagnets, making junctions with MgO barrier and orthogonal magnetization configuration a promising high magnetic field sensor.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
07.55.-w Magnetic instruments and components

Magnetic properties of phthalocyanine-based organometallic nanowire

Yandong Ma, Ying Dai, Zhenkui Zhang, Lin Yu, and Baibiao Huang

Appl. Phys. Lett. 101, 062405 (2012); http://dx.doi.org/10.1063/1.4744437 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Using first principles calculations, we investigate the electronic and magnetic properties of transition metal phthalocyanine (M-Pc, M = Cr, Mn, Co, Ni, Cu, and Zn) nanowire (M-PcNW). Our calculations show that Ni-PcNW and Zn-PcNW are nonmagnetic, while Cr-PcNW and Cu-PcNW are antiferromagnetic with small energy difference and Co-PcNW show paramagnetic due to their long spin coherence length. Most importantly, we predicate that Mn-PcNW frameworks display long-ranged ferromagnetic spin ordering, offering strong spin polarization around Fermi level. Moreover, Mn-PcNW frameworks are half-metals, which make Mn-PcNW frameworks ideal candidates for spintronic devices. These results may shed light on further experimental studies on molecular spintronics.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.22.-f Electronic structure of nanoscale materials and related systems

Magnetoelectric effects at microwave frequencies on Z-type hexaferrite

Khabat Ebnabbasi, Marjan Mohebbi, and Carmine Vittoria

Appl. Phys. Lett. 101, 062406 (2012); http://dx.doi.org/10.1063/1.4744591 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2012

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Converse microwave measurements have been performed to measure magnetoelectric effects at room temperature on Sr3Co2Fe24O41 hexaferrite slabs. The measured properties include the magnetic permeability and strain as a function of the electric field E. In this paper, the microwave permeability changes are due to the application of a DC voltage affecting the static magnetization rather than shifts in ferromagnetic resonance. We conclude that when an electric field is turned on the ferrite exhibits broken symmetries for time reversal and parity.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Influence of thermal fluctuations on the emission linewidth in MgO-based spin transfer oscillators

J. F. Sierra, M. Quinsat, F. Garcia-Sanchez, U. Ebels, I. Joumard, A. S. Jenkins, B. Dieny, M.-C. Cyrille, A. Zeltser, and J. A. Katine

Appl. Phys. Lett. 101, 062407 (2012); http://dx.doi.org/10.1063/1.4744924 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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The temperature dependence of the microwave emission linewidth Δf, the amplitude-phase coupling parameter ν, and the amplitude relaxation rate Γp were investigated experimentally for tunnel junction spin-transfer-oscillators. A linear increase of Δf and unexpectedly of Γp with temperature is observed, giving a ratio 2πΔf/Γp close to one. Analytical evaluation of the phase variance confirms that for this ratio the temperature dependence of Δf is linear and that in this temperature range Δf is enhanced by the amplitude-phase coupling. This is not changed when taking the temperature dependence of Γp into account, the origin of which remains to be elucidated.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.-x Radiowave and microwave (including millimeter wave) technology

Current-induced synchronized switching of magnetization

Soo-Man Seo and Kyung-Jin Lee

Appl. Phys. Lett. 101, 062408 (2012); http://dx.doi.org/10.1063/1.4742917 (5 pages) | Cited 2 times

Online Publication Date: 7 August 2012

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We investigate current-induced magnetization switching for a multilayer structure that allows a reduced switching current while maintaining high thermal stability of the magnetization. The structure consists of a perpendicular polarizer, a perpendicular free-layer, and an additional free-layer having in-plane magnetization. When the current runs perpendicular to the structure, the in-plane free-layer undergoes a precession and supplies an internal rf field to the perpendicular free-layer, resulting in a reduced switching current for one current polarity. For the other polarity, the in-plane free-layer almost saturates perpendicular to the plane and acts as another perpendicular polarizer, which also reduces the switching current.
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75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.30.Gw Magnetic anisotropy
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Mg Numerical simulation studies

Electrical determination of relative chirality direction in a Co/Cu/Co ferromagnetic ring

A. S. Demiray, M. Kohda, T. Miyawaki, Y. Watanabe, K. Saito, S. Mitani, K. Takanashi, and J. Nitta

Appl. Phys. Lett. 101, 062409 (2012); http://dx.doi.org/10.1063/1.4743004 (5 pages)

Online Publication Date: 7 August 2012

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We have studied a Co/Cu/Co trilayer circular ring by using a current-in-plane giant magnetoresistance (GMR) method. When the applied field angle is shifted from the current probes, four distinctive magnetization reversal patterns are obtained depending on the vortex chirality configurations in the top and bottom rings. During the repeated GMR measurements, two GMR patterns are preferentially appeared and it turns out that the same chirality is favorable between the top and the bottom rings. Micromagnetic simulation reproduces the experimental data by taking into account the domain wall shift at the onion states.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Carrier-dopant exchange interactions in Mn-doped PbS colloidal quantum dots

Gen Long, Biplob Barman, Savas Delikanli, Yu Tsung Tsai, Peihong Zhang, Athos Petrou, and Hao Zeng

Appl. Phys. Lett. 101, 062410 (2012); http://dx.doi.org/10.1063/1.4743010 (4 pages)

Online Publication Date: 7 August 2012

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Carrier-dopant exchange interactions in Mn-doped PbS colloidal quantum dots were studied by circularly polarized magneto-photoluminescence. Mn substitutional doping leads to paramagnetic behavior down to 5 K. While undoped quantum dots show negative circular polarization, Mn doping changes its sign to positive. A circular polarization value of 40% was achieved at T = 7 K and B = 7 tesla. The results are interpreted in terms of Zeeman splitting of the band edge states in the presence of carrier-dopant exchange interactions that are qualitatively different from the s,p-d exchange interactions in II-VI systems.
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78.20.Ls Magneto-optical effects
78.55.Hx Other solid inorganic materials
61.72.up Other materials
75.20.Ck Nonmetals
75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors

Mechanism of the giant irreversible positive magnetic entropy change in a Tb-based bulk metallic glass

Qiang Luo, Björn Schwarz, Norbert Mattern, Jun Shen, and Jürgen Eckert

Appl. Phys. Lett. 101, 062411 (2012); http://dx.doi.org/10.1063/1.4743014 (5 pages)

Online Publication Date: 7 August 2012

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A suitable coherent description of the reversible and irreversible magnetic entropy changes in a Tb-based metallic glass with strong random magnetic anisotropy (RMA) is presented. A giant irreversible positive magnetic entropy change is observed from magnetic measurements at low temperatures, which is found to arise from the entropy production, while a small negative one is obtained from heat capacity measurements. The temperature dependences of the irreversible positive magnetic entropy change under a field change of 5 T and the internal entropy production in the initial magnetization process can be described by an exponential law, which is determined by RMA.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.43.Fs Glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials

Nanoscale magnetic tunnel junction sensors with perpendicular anisotropy sensing layer

Z. M. Zeng, P. Khalili Amiri, J. A. Katine, J. Langer, K. L. Wang, and H. W. Jiang

Appl. Phys. Lett. 101, 062412 (2012); http://dx.doi.org/10.1063/1.4744914 (4 pages)

Online Publication Date: 7 August 2012

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A nano-scale linear magnetoresistance sensor is demonstrated using magnetic tunnel junctions with an in-plane magnetized reference layer and a sensing layer with interfacial perpendicular anisotropy. We show that the sensor response depends critically on the thickness of the sensing layer since its perpendicular anisotropy is significantly associated with thickness. The optimized sensors exhibit a large field sensitivity of up to 0.02% MR/Oe and a high linear field range of up to 600 Oe. These findings imply that this sensing scheme is a promising method for developing nano-scale magnetic sensors with simple design, high sensitivity, and low power consumption.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
07.55.-w Magnetic instruments and components
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Accurate determination of the specific absorption rate in superparamagnetic nanoparticles under non-adiabatic conditions

F. J. Teran, C. Casado, N. Mikuszeit, G. Salas, A. Bollero, M. P. Morales, J. Camarero, and R. Miranda

Appl. Phys. Lett. 101, 062413 (2012); http://dx.doi.org/10.1063/1.4742918 (4 pages) | Cited 2 times

Online Publication Date: 8 August 2012

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We report on a general description of non-adiabatic calorimetry measurements for improving the accuracy on the determination of the specific absorption rate of superparamagnetic nanoparticles subjected to alternating magnetic fields. We perform experiments on reduced volumes of iron oxide nanoparticles dispersed in aqueous media under different thermal equilibrium conditions. We introduce a simple model, which considers linear thermal losses to precisely reproduce the complete time evolution of temperature. The control and the quantification of heat losses lead to higher accuracy for determining the specific absorption rate in superparamagnetic nanoparticles.
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75.75.Jn Dynamics of magnetic nanoparticles
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.50.Tt Fine-particle systems; nanocrystalline materials
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
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