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17 Sep 2012

Volume 101, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He
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Electric field-induced magnetization reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction

S. Kanai, M. Yamanouchi, S. Ikeda, Y. Nakatani, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 101, 122403 (2012); http://dx.doi.org/10.1063/1.4753816 (3 pages) | Cited 6 times

Online Publication Date: 18 September 2012

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The electric field-induced ∼180° magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Spin transfer torque devices utilizing the giant spin Hall effect of tungsten

Chi-Feng Pai, Luqiao Liu, Y. Li, H. W. Tseng, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 101, 122404 (2012); http://dx.doi.org/10.1063/1.4753947 (4 pages) | Cited 6 times

Online Publication Date: 18 September 2012

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We report a giant spin Hall effect in β-W thin films. Using spin torque induced ferromagnetic resonance with a β-W/CoFeB bilayer microstrip, we determine the spin Hall angle to be |θSHβ-W| = 0.30±0.02, large enough for an in-plane current to efficiently reverse the orientation of an in-plane magnetized CoFeB free layer of a nanoscale magnetic tunnel junction adjacent to a thin β-W layer. From switching data obtained with such 3-terminal devices, we independently determine |θSHβ-W| = 0.33±0.06. We also report variation of the spin Hall switching efficiency with W layers of different resistivities and hence of variable (α and β) phase composition.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.75.-c Magnetic properties of nanostructures
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport

Rashba spin-orbit-interaction-based quantum pump in graphene

Dario Bercioux, Daniel F. Urban, Francesco Romeo, and Roberta Citro

Appl. Phys. Lett. 101, 122405 (2012); http://dx.doi.org/10.1063/1.4753975 (4 pages) | Cited 2 times

Online Publication Date: 18 September 2012

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We present a proposal for an adiabatic quantum pump based on a graphene monolayer patterned by electrostatic gates and operated in the low-energy Dirac regime. The setup under investigation works in the presence of inhomogeneous spin-orbit interactions of intrinsic- and Rashba-type and allows to generate spin polarized coherent currents. A local spin polarized current is induced by the pumping mechanism assisted by the spin-double refraction phenomenon.
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73.61.Wp Fullerenes and related materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.25.-b Spin polarized transport

Magnetic anisotropy and anomalous transitions in TbMnO3 thin films

Yimin Cui, Yufeng Tian, Aixian Shan, Chinping Chen, and Rongming Wang

Appl. Phys. Lett. 101, 122406 (2012); http://dx.doi.org/10.1063/1.4754544 (5 pages) | Cited 2 times

Online Publication Date: 19 September 2012

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TbMnO3 thin films with different crystallographic orientations were deposited epitaxially on LaAlO3 [100] and SrTiO3 [100] single crystal substrates by using pulsed laser deposition. Magnetization measurements were performed along the [110], [−110], and [001] directions of the films. Obvious magnetic anisotropy and low temperature ferromagnetism were found. Transitions at T ∼ 10, 32, 120, and 125 K along different directions are observed. The susceptibility anomalies, remarkably anisotropic, are discussed on the frame of the domain wall and strain-induced distortion. Particularly, the lattice mismatch and the anisotropic thermal expansion between the films and substrates are likely responsible for the distortion behaviors.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure

Assembly of uniaxially aligned rare-earth-free nanomagnets

B. Balamurugan, B. Das, V. R. Shah, R. Skomski, X. Z. Li, and D. J. Sellmyer

Appl. Phys. Lett. 101, 122407 (2012); http://dx.doi.org/10.1063/1.4753950 (5 pages) | Cited 3 times

Online Publication Date: 19 September 2012

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We report HfCo7 nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K1 ≈ 10 Mergs/cm3, coercivity Hc ≈ 4.4 kOe, and magnetic polarization Js ≈ 10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having Js as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This study suggests HfCo7 as a promising rare-earth-free permanent-magnet alloy, which is important for mitigating the critical-materials aspects of rare-earth elements.
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81.16.Dn Self-assembly
81.40.Gh Other heat and thermomechanical treatments
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.50.Ww Permanent magnets

Perpendicular magnetization of Co20Fe50Ge30 films induced by MgO interface

Manli Ding and S. Joseph Poon

Appl. Phys. Lett. 101, 122408 (2012); http://dx.doi.org/10.1063/1.4754001 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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Epitaxial growth of Co20Fe50Ge30 films on single crystal MgO (001) substrate is reported. Structure characterization revealed (001)-oriented B2 order of Co20Fe50Ge30, well lattice matched with the MgO barrier. Perpendicular magnetic anisotropy was achieved in the MgO/Co20Fe50Ge30/MgO structure with an optimized magnetic anisotropy energy density of 2 × 106 erg/cm3. The magnetic anisotropy is found to depend strongly on the thickness of the MgO and Co20Fe50Ge30 layers, indicating that the perpendicular magnetic anisotropy of Co20Fe50Ge30 is contributed by the interfacial anisotropy between Co20Fe50Ge30 and MgO. With reported low damping constant, Co20Fe50Ge30 films are promising spintronic materials for achieving low switching current.
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75.30.Gw Magnetic anisotropy
75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.A- Nucleation and growth
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Exchange bias coupling of Co with ultrathin La2/3Sr1/3MnO3 films

Y. J. Shi, Y. Zhou, H. F. Ding, F. M. Zhang, L. Pi, Y. H. Zhang, and D. Wu

Appl. Phys. Lett. 101, 122409 (2012); http://dx.doi.org/10.1063/1.4754594 (4 pages)

Online Publication Date: 20 September 2012

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Magnetic properties of epitaxially grown ultrathin La2/3Sr1/3MnO3 (LSMO) films down to a thickness of one unit cell (u.c.) have been systematically investigated by studying their magnetic behaviors with Co capping layers. For LSMO thickness below 3 u.c., the Co/LSMO bilayers exhibit strong exchange bias (EB) effects after field cooling, suggesting the existence of antiferromagnetic (AFM) phase at the interfaces in ultrathin LSMO. The presence of exchange bias effect for the bilayer with 1 u.c. thick LSMO further demonstrates that the AFM ordering of the LSMO is C-type AFM ordering structure. For 10 u.c. LSMO, the magnetic properties are clearly not altered by the capping Co film, suggesting that the observed phenomena are caused by the intrinsic properties of LSMO.
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75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.at Other materials

Spintronic oscillator based on magnetic field feedback

D. Dixit, K. Konishi, C. V. Tomy, Y. Suzuki, and A. A. Tulapurkar

Appl. Phys. Lett. 101, 122410 (2012); http://dx.doi.org/10.1063/1.4752008 (4 pages) | Cited 1 time

Online Publication Date: 20 September 2012

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We present a circuit design of a spintronic oscillator based on a magnetic tunnel junction (MTJ). In this design, a dc current is passed through a magnetic tunnel junction which is connected to a “feed-back” wire below it. Any fluctuation in the magnetization direction of the free layer of MTJ, drives a fluctuating current through the feed-back wire, which exerts a magnetic field on the free layer. This in turn can amplify the magnetization fluctuations. If the dc current passing through the MTJ is more than a critical value, periodic precessional states of the magnetization are possible.
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84.30.Ng Oscillators, pulse generators, and function generators
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Spin gating electrical current

C. Ciccarelli, L. P. Zârbo, A. C. Irvine, R. P. Campion, B. L. Gallagher, J. Wunderlich, T. Jungwirth, and A. J. Ferguson

Appl. Phys. Lett. 101, 122411 (2012); http://dx.doi.org/10.1063/1.4752013 (4 pages)

Online Publication Date: 20 September 2012

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The level of the chemical potential is a fundamental parameter of the electronic structure of a physical system, which consequently plays an important role in defining the properties of active electrical devices. We directly measure the chemical potential shift in the relativistic band structure of the ferromagnetic semiconductor (Ga,Mn)As, controlled by changes in its magnetic order parameter. Our device comprises a non-magnetic aluminum single electron channel capacitively coupled to the (Ga,Mn)As gate electrode. The chemical potential shifts of the gate are directly read out from the shifts in the Coulomb blockade oscillations of the single electron transistor. The experiments introduce a concept of spin gating electrical current. In our spin transistor spin manipulation is completely removed from the electrical current carrying channel.
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85.35.Gv Single electron devices
65.40.G- Other thermodynamical quantities
71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors

Magnetization reversal in multisegmented nanowires: Parallel and serial reversal modes

S. Allende, N. M. Vargas, D. Altbir, V. Vega, D. Görlitz, and K. Nielsch

Appl. Phys. Lett. 101, 122412 (2012); http://dx.doi.org/10.1063/1.4754117 (4 pages)

Online Publication Date: 20 September 2012

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We investigate the effect of the dipolar magnetic interaction between magnetic layers mediated by non-magnetic ones in multisegmented nanowires. Multiple symmetric and non-symmetric segments are considered. We observe that due to the dipolar interaction, the magnetization reversal can follow two possible routes, a serial, or a parallel reversal process. We show that by using asymmetrical multi-segmented wires it is possible to stop the magnetization reversal of the system at any particular point.
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75.60.Jk Magnetization reversal mechanisms
75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities

Effect of spin drift on spin accumulation voltages in highly doped silicon

Makoto Kameno, Yuichiro Ando, Eiji Shikoh, Teruya Shinjo, Tomoyuki Sasaki, Tohru Oikawa, Yoshishige Suzuki, Toshio Suzuki, and Masashi Shiraishi

Appl. Phys. Lett. 101, 122413 (2012); http://dx.doi.org/10.1063/1.4754285 (4 pages) | Cited 5 times

Online Publication Date: 20 September 2012

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We investigated the effect of spin drift on spin accumulation in highly doped silicon (Si) by using a non-local three-terminal (NL-3T) and four-terminal (NL-4T) methods, and have clarified that the spin accumulation voltages in a NL-3T device were modulated due to spin drift and that spin lifetime can be accurately extracted by employing a modified spin drift-diffusion equation. The extracted spin lifetime is 4-7 ns, which is slightly shorter than the intrinsic spin lifetime (8 ns) measured in the NL-4T method in the same Si device because of spin drift. It is elucidated that the spin drift effect should be considered for the precise estimation of spin lifetime in Si by NL-3T method.
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75.30.Ds Spin waves
75.30.Wx Spin crossover
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
61.72.uf Ge and Si
75.78.-n Magnetization dynamics

Effect of Mg interlayer on perpendicular magnetic anisotropy of CoFeB films in MgO/Mg/CoFeB/Ta structure

Q. L. Ma, S. Iihama, T. Kubota, X. M. Zhang, S. Mizukami, Y. Ando, and T. Miyazaki

Appl. Phys. Lett. 101, 122414 (2012); http://dx.doi.org/10.1063/1.4754118 (5 pages) | Cited 2 times

Online Publication Date: 21 September 2012

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The effects of Mg metallic interlayer on the magnetic properties of thin CoFeB films in MgO/Mg (tMg)/CoFeB (1.2 nm)/Ta structures were studied in this letter. Our experimental result shows that the CoFeB film exhibits perpendicular magnetic anisotropy (PMA) when the CoFeB and MgO layers are separated by a metallic Mg layer with a maximum thickness of 0.8 nm. The origin of PMA was discussed by considering the preferential transmission of the Δ1 symmetry preserved by the Mg interlayer in crystallized MgO/Mg/CoFeB/Ta. In addition, the thin Mg interlayer also contributes to enhancing the thermal stability and reducing the effective damping constant and coercivity of the CoFeB film.
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81.05.Bx Metals, semimetals, and alloys
68.60.Dv Thermal stability; thermal effects
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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Nanoparticle magnetization measurements by a high sensitive nano-superconducting quantum interference device

R. Russo, C. Granata, E. Esposito, D. Peddis, C. Cannas, and A. Vettoliere

Appl. Phys. Lett. 101, 122601 (2012); http://dx.doi.org/10.1063/1.4751036 (4 pages) | Cited 2 times

Online Publication Date: 17 September 2012

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A high sensitive nano superconducting quantum interference device (nanoSQUID) operating as a magnetic flux to critical current transducer with a suitable feedback circuit is employed to measure the magnetization of ferrimagnetic iron oxide nanoparticles. An improved SQUID responsivity has been obtained by using a loop inductance asymmetry. Iron oxide nanoparticles having a mean diameter of 8 nm have been excited by applying a polarizing field in the plane of the nanoSQUID loop. The field dependence of the nanoparticle magnetization at T = 4.2 K shows magnetic hysteresis. Magnetic relaxation measurements are reported and compared with those obtained by using a commercial measurement system.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
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Elucidating the mechanism for indentation size-effect in dielectrics

C. R. Robinson, K. W. White, and P. Sharma

Appl. Phys. Lett. 101, 122901 (2012); http://dx.doi.org/10.1063/1.4753799 (2 pages)

Online Publication Date: 17 September 2012

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Recent work presented experimental evidence of a strong elastic indentation size-effect in ferroelectric BaTiO3. The apparent elastic modulus was shown to exhibit significant stiffening with decreasing contact size and this was attributed to the phenomenon of flexoelectricity. There is however room for debate whether domain wall movement, nucleation, and related phenomena are responsible for the size-effect in BaTiO3. In this work, we present a nanoindentation study of paraelectric SrTiO3 and argue that indeed flexoelectricity rather than ferroelectric-specific effects cause the observed size dependent behavior.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli
62.20.Qp Friction, tribology, and hardness
77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis
81.40.Jj Elasticity and anelasticity, stress-strain relations

Residual stresses and clamped thermal expansion in LiNbO3 and LiTaO3 thin films

A. Bartasyte, V. Plausinaitiene, A. Abrutis, T. Murauskas, P. Boulet, S. Margueron, J. Gleize, S. Robert, V. Kubilius, and Z. Saltyte

Appl. Phys. Lett. 101, 122902 (2012); http://dx.doi.org/10.1063/1.4752448 (5 pages) | Cited 2 times

Online Publication Date: 17 September 2012

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Residual stresses in LiNbO3 and LiTaO3 epitaxial thin films were evaluated taking into account Li nonstoichiometry by means of Raman spectroscopy and x-ray diffraction. The epitaxial films were grown on C-cut sapphire substrates by pulsed injection metal organic chemical vapour deposition. Clamping of the epitaxial films by the substrate induced a transfer from the in plane thermal expansion to the out of plane component. The temperature of the phase transition of clamped LiTaO3 films was close to that expected for a bulk sample.
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68.60.Bs Mechanical and acoustical properties
65.40.De Thermal expansion; thermomechanical effects
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Synthesis and room temperature four-state memory prototype of Sr3Co2Fe24O41 multiferroics

Jiangtao Wu, Zhan Shi, Jun Xu, Nan Li, Zhibin Zheng, Hao Geng, Zhaoxiong Xie, and Lansun Zheng

Appl. Phys. Lett. 101, 122903 (2012); http://dx.doi.org/10.1063/1.4753973 (4 pages) | Cited 2 times

Online Publication Date: 18 September 2012

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Multiferroics exhibit both ferroelectricity and ferromagnetism. The combination of ferroelectricity and ferromagnetism in single phase offers the ability to obtain four physical polarization states, i.e., two electric polarization combined with two magnetic polarization states, achieving four-state memory devices. The four-state memory devices can exponentially increase data storage capacity. In this letter, we synthesized single phase Sr3Co2Fe24O41, which exhibits ferroelectricity, ferromagnetism, and magnetoelectric coupling effect at room temperature. The as-prepared Sr3Co2Fe24O41 was used as a four-state memory prototype. The information was written by electric and magnetic fields, and read out by magnetoelectric coefficient (αE) with the help of a small bias magnetic field.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Dd Nonmetallic ferromagnetic materials
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
84.30.Sk Pulse and digital circuits

Coexistence of coupled magnetic phases in epitaxial TbMnO3 films revealed by ultrafast optical spectroscopy

J. Qi, L. Yan, H. D. Zhou, J.-X. Zhu, S. A. Trugman, A. J. Taylor, Q. X. Jia, and R. P. Prasankumar

Appl. Phys. Lett. 101, 122904 (2012); http://dx.doi.org/10.1063/1.4754294 (4 pages)

Online Publication Date: 19 September 2012

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Ultrafast optical pump-probe spectroscopy is used to reveal the coexistence of coupled antiferromagnetic/ferroelectric and ferromagnetic orders in multiferroic TbMnO3 films through their time domain signatures. Our observations are explained by a theoretical model describing the coupling between reservoirs with different magnetic properties. These results can guide researchers to creating unique kinds of multiferroic materials that combine coupled ferromagnetic, antiferromagnetic, and ferroelectric properties in one compound.
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75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.47.J- Ultrafast spectroscopy (<1 psec)

The thickness and stretch dependence of the electrical breakdown strength of an acrylic dielectric elastomer

Jiangshui Huang, Samuel Shian, Roger M. Diebold, Zhigang Suo, and David R. Clarke

Appl. Phys. Lett. 101, 122905 (2012); http://dx.doi.org/10.1063/1.4754549 (4 pages) | Cited 3 times

Online Publication Date: 21 September 2012

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The performance of dielectric elastomer actuators is limited by electrical breakdown. Attempts to measure this are confounded by the voltage-induced thinning of the elastomer. A test configuration is introduced that avoids this problem: A thin sheet of elastomer is stretched, crossed-wire electrodes are attached, and then embedded in a stiff polymer. The applied electric field at breakdown, EB, is found to depend on both the deformed thickness, h, and the stretch applied, λ. For the acrylic elastomer investigated, the breakdown field scales as EB  =  51  h − 0.25  λ 0.63. The test configuration allows multiple individual tests to be made on the same sheet of elastomer.
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77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
81.70.-q Methods of materials testing and analysis
68.35.bm Polymers, organics
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High sensitivity SQUID-detection and feedback-cooling of an ultrasoft microcantilever

A. Vinante, A. Kirste, A. den Haan, O. Usenko, G. Wijts, E. Jeffrey, P. Sonin, D. Bouwmeester, and T. H. Oosterkamp

Appl. Phys. Lett. 101, 123101 (2012); http://dx.doi.org/10.1063/1.4752766 (4 pages)

Online Publication Date: 17 September 2012

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We measure the motion of an ultrasoft cantilever, carrying a ferromagnetic particle, by means of a superconducting quantum interference device (SQUID). In our scheme, the cantilever motion modulates the magnetic flux in the SQUID due to the coupling with the magnetic particle. For the cantilever fundamental mode, cooled to temperatures below 100 mK, we achieve a dimensionless coupling factor as large as 0.07, displacement sensitivity of 200 fm/math, and subattonewton force sensitivity. We demonstrate the outstanding combination of very low displacement and force noise by feedback-cooling the cantilever mode to an effective mode temperature of 160 μK.
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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
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Depolarization effect in optical absorption measurements of one- and two-dimensional nanostructures

Lihong H. Herman, Cheol-Joo Kim, Zenghui Wang, Moon-Ho Jo, and Jiwoong Park

Appl. Phys. Lett. 101, 123102 (2012); http://dx.doi.org/10.1063/1.4752889 (4 pages)

Online Publication Date: 17 September 2012

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We measure absolute optical absorption cross-sections of one- (1D) and two-dimensional (2D) nanostructures using a focused laser beam while varying the numerical aperture (NA) of the focusing lens. We find the optical absorption deviates at higher NA. In the high NA regime, absorption by graphene decreases from 2.2% to below 1.8%; for Ge nanowires, it decreases from an expected value by a factor of 1.2. We explain this using the depolarization effect at the focal spot and conclude that these corrections allow for accurate quantitative measurements of optical and optoelectronic processes in 1D or 2D nanostructures.
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78.67.Uh Nanowires
78.67.Wj Optical properties of graphene
81.07.Gf Nanowires
78.40.Fy Semiconductors
78.40.Ri Fullerenes and related materials
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)

Growth processes of lithium titanate thin films deposited by using pulsed laser deposition

Akichika Kumatani, Takeo Ohsawa, Ryota Shimizu, Yoshitaka Takagi, Susumu Shiraki, and Taro Hitosugi

Appl. Phys. Lett. 101, 123103 (2012); http://dx.doi.org/10.1063/1.4752466 (4 pages)

Online Publication Date: 17 September 2012

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We have investigated the pulsed laser deposition (PLD) growth processes of spinel lithium titanates based on the preparation of Li4Ti5O12 and LiTi2O4 from a Li4Ti5O12 target. The Li/Ti atomic ratio of the species arriving at substrate during the deposition was only ∼0.5. The LiTi2O4 epitaxial thin films fabricated on MgAl2O4 (111) substrate exhibited high conductivity at room temperature (∼3.0 × 103 Ω−1 cm−1) and a superconducting transition temperature of ∼12 K. These values are the highest reported for epitaxial thin films. Our results demonstrate the importance of the target composition, providing further insights into the Li-containing metal oxide deposition processes using PLD.
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81.15.Fg Pulsed laser ablation deposition
74.62.Yb Other effects
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
68.55.-a Thin film structure and morphology

Nanoscale frictional characteristics of graphene nanoribbons

Jiangnan Zhang, Wei Lu, James M. Tour, and Jun Lou

Appl. Phys. Lett. 101, 123104 (2012); http://dx.doi.org/10.1063/1.4752724 (5 pages)

Online Publication Date: 18 September 2012

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We compare nanoscale frictional characteristics of three types of chemically treated graphene nanoribbons (GNRs) via atomic force microscope. Measurements in both ambient and low humidity conditions demonstrate that covalently bonded functional groups have a significant impact on the frictional response of GNRs. The measured tip-sample adhesion forces seem to support the observed friction force dependence on functionalizations, and the friction and adhesion differences could also be attributed to the surface reactivity and hydrophilicity differences induced by different chemical functionalization schemes.
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62.25.-g Mechanical properties of nanoscale systems
81.07.Bc Nanocrystalline materials
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
61.48.Gh Structure of graphene
81.05.ue Graphene

Magnetic properties of MoS2: Existence of ferromagnetism

Sefaattin Tongay, Sima S. Varnoosfaderani, Bill R. Appleton, Junqiao Wu, and Arthur F. Hebard

Appl. Phys. Lett. 101, 123105 (2012); http://dx.doi.org/10.1063/1.4753797 (4 pages) | Cited 5 times

Online Publication Date: 18 September 2012

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We report on the magnetic properties of MoS2 measured from room temperature down to 10 K and magnetic fields up to 5 T. We find that single crystals of MoS2 display ferromagnetism superimposed onto large temperature-dependent diamagnetism and have observed that ferromagnetism persists from 10 K up to room temperature. We attribute the existence of ferromagnetism partly to the presence of zigzag edges in the magnetic ground state at the grain boundaries. Since the magnetic measurements are relatively insensitive to the interlayer coupling, these results are expected to be valid in the single layer limit.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials

Influence of surface plasmon propagation on leakage radiation microscopy imaging

S. Aberra Guebrou, J. Laverdant, C. Symonds, S. Vignoli, F. Bessueille, and J. Bellessa

Appl. Phys. Lett. 101, 123106 (2012); http://dx.doi.org/10.1063/1.4753809 (4 pages)

Online Publication Date: 18 September 2012

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We study in this Letter, the effect of the surface plasmon (SP) propagation and coherence on the images obtained by leakage radiation microscopy. The studied system is a set of nanocrystals deposited on a thin silver film supporting surface plasmon modes. More than 70% of the emission in this typical system comes from non-local emission. The diameter of the influence circle around the detection point is of the order of magnitude of the plasmon propagation length. We also present an original method to measure the propagation length (Lspp) of surface plasmons in complex systems by a two Young's slits experiment. This method can be useful for complex systems with a very short propagation length.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.La Quantum dots
73.22.Lp Collective excitations
81.07.Ta Quantum dots
81.16.-c Methods of micro- and nanofabrication and processing
68.65.Hb Quantum dots (patterned in quantum wells)

Catalyst-free synthesis of reduced graphene oxide–carbon nanotube hybrid materials by acetylene-assisted annealing graphene oxide

Fuchi Liu, Ming Li, Qian Feng, Nujiang Tang, Wei Zhong, Wei Huang, and Youwei Du

Appl. Phys. Lett. 101, 123107 (2012); http://dx.doi.org/10.1063/1.4753928 (3 pages)

Online Publication Date: 18 September 2012

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A facile catalyst-free approach for synthesis of reduced graphene oxide-carbon nanotube (RGO-CNT) hybrid materials was presented by acetylene-assisted annealing graphene oxide. The weight ratio of CNTs to RGO can be adjusted by regulating the annealing temperature, and it can be tuned in a relatively wide range of 0.33 to 7.039. The catalyst-free method opens up the possibility for the synthesis of RGO-CNTs for various applications.
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81.05.uj Diamond/nanocarbon composites
81.07.De Nanotubes
81.40.Gh Other heat and thermomechanical treatments
81.05.ue Graphene
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