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13 Feb 2012

Volume 100, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 073501 (2012); http://dx.doi.org/10.1063/1.3682479 (3 pages)

S. Tongay, M. Lemaitre, J. Fridmann, A. F. Hebard, B. P. Gila, and B. R. Appleton
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Role of aluminum as an oxygen-scavenger in zirconium based bulk metallic glasses

Jochen Heinrich, Ralf Busch, Frank Müller, Samuel Grandthyll, and Stefan Hüfner

Appl. Phys. Lett. 100, 071909 (2012); http://dx.doi.org/10.1063/1.3685492 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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In order to investigate a way to diminish the impact of oxygen onto the critical cooling rate of Zr-based alloys, the bonding chemistry of the elements in Zr-Cu-Ni-Al-Nb-Si bulk metallic glasses with different oxygen contents is studied by x-ray photoelectron spectroscopy. Complementary undercooling experiments lead to continuous-cooling-transformation diagrams for the studied alloys. The experimental results demonstrate that Al not only acts as a scavenger for both absorbed and intrinsic oxygen but the dissolution of its oxide on atomic length scales refrains from heterogeneous nucleation. The combined effect is an enhancement of oxygen tolerance in the investigated alloy.
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61.43.Fs Glasses
61.50.Lt Crystal binding; cohesive energy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.30.Dz Phase diagrams of other materials
79.60.Ht Disordered structures
64.60.qj Studies of nucleation in specific substances

Well-to-well non-uniformity in InGaN/GaN multiple quantum wells characterized by capacitance-voltage measurement with additional laser illumination

Tae-Soo Kim, Byung-Jun Ahn, Yanqun Dong, Ki-Nam Park, Jin-Gyu Lee, Youngboo Moon, Hwan-Kuk Yuh, Sung-Chul Choi, Jae-Hak Lee, Soon-Ku Hong, and Jung-Hoon Song

Appl. Phys. Lett. 100, 071910 (2012); http://dx.doi.org/10.1063/1.3685717 (4 pages) | Cited 2 times

Online Publication Date: 16 February 2012

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We experimentally investigated well-to-well non-uniformity in InGaN/GaN multiple quantum well (MQW) structures by using capacitance-voltage measurements with additional laser illumination. By varying the illuminating power of the resonant excitation, well-to-well non-uniformity through the MQWs was clearly revealed. The quantum wells (QWs) close to the n-GaN side show higher carrier accumulations and larger position shift as the excitation power is increased, relative to the p-side QWs. Both results were attributed to the existence of stronger piezoelectric fields in the n-side QWs induced by subsequent partial relaxation of strain through the MQWs.
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73.61.Ey III-V semiconductors

Dirac cones at math = 0 in acoustic crystals and zero refractive index acoustic materials

Fengming Liu, Xueqin Huang, and C. T. Chan

Appl. Phys. Lett. 100, 071911 (2012); http://dx.doi.org/10.1063/1.3686907 (4 pages) | Cited 8 times

Online Publication Date: 16 February 2012

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We show that two-dimensional acoustic crystals (ACs) can be designed to exhibit Dirac cone dispersion at math = 0. Effective medium theory finds that some of these ACs can have effectively zero reciprocal of bulk modulus 1/κeff and zero mass density ρeff, and thus zero refractive indices at the Dirac point. Numerical simulations are used to demonstrate various phenomena associated with the zero spatial phase change inside such materials.
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62.65.+k Acoustical properties of solids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations

Temperature-dependent decay dynamics in highly mismatched ZnSe1−xTex alloy

Yan-Cheng Lin, Wei-Shi Jiang, Wu-Ching Chou, Wei-Kuo Chen, Wen-Hao Chang, Chin-Hau Chia, Cheng-Yu Chen, and Jen-Inn Chyi

Appl. Phys. Lett. 100, 071912 (2012); http://dx.doi.org/10.1063/1.3687187 (4 pages)

Online Publication Date: 17 February 2012

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This study investigates the temperature-dependent decay dynamics in highly mismatched ZnSe0.950Te0.050 alloy using photoluminescence (PL) and time-resolved PL spectroscopy. The PL peak energy exhibits a V-shaped dependence on temperature (10–300 K), indicating strong carrier localization. Kohlrausch’s stretched exponential law, in which the deduced stretching exponent β is highly consistent with the V-shaped PL peak shift, closely corresponds to the complex decay curves over a wide temperature range. Additionally, the PL lifetime τ initially increases and then monotonically declines as the temperature increases. These findings agree excellently with the low electron-hole binding energy upon thermal ionization of weakly bound electrons.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
78.47.jd Time resolved luminescence

Properties of InxGa1−xN films in terahertz range

A. Gauthier-Brun, J. H. Teng, E. Dogheche, W. Liu, A. Gokarna, M. Tonouchi, S. J. Chua, and D. Decoster

Appl. Phys. Lett. 100, 071913 (2012); http://dx.doi.org/10.1063/1.3684836 (5 pages) | Cited 1 time

Online Publication Date: 17 February 2012

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In this letter, we report the characterization of the refractive indices and complex conductivities of a set of GaN films with different carrier concentrations, InN film, and InxGa1−xN films with indium content varying from x = 0.07 to x = 0.14 grown by metalorganic chemical vapor deposition for frequencies ranging from 0.3 to 3 THz using terahertz time-domain spectroscopy (THz-TDS). The refractive indices of InxGa1−xN films at THz range are reported. The carrier density and mobility determined using THz-TDS method show good agreement with four-probe Hall measurements.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.80.Ey III-V and II-VI semiconductors
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Mechanism for resistive switching in an oxide-based electrochemical metallization memory

Shanshan Peng, Fei Zhuge, Xinxin Chen, Xiaojian Zhu, Benlin Hu, Liang Pan, Bin Chen, and Run-Wei Li

Appl. Phys. Lett. 100, 072101 (2012); http://dx.doi.org/10.1063/1.3683523 (4 pages) | Cited 10 times

Online Publication Date: 13 February 2012

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A comparison of the asymmetric OFF-state current-voltage characteristics between Cu/ZnO/Pt and Cu/ZnO/Al-doped ZnO (AZO) electrochemical metallization memory (ECM) cells demonstrates that the Cu filament rupture and rejuvenation occur at the ZnO/Pt (or AZO) interface, i.e., the cathodic interface. Therefore, the filament is most likely to have a conical shape, with wider and narrower diameters formed at the anodic and cathodic interfaces, respectively. It is inferred that the filament growth starts at the anode surface and stops at the cathode surface. Our results indicate that oxide-based ECM cells strongly differ from sulfide- and selenide-based ones in the resistive switching mechanism.
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84.30.Sk Pulse and digital circuits
85.40.Ls Metallization, contacts, interconnects; device isolation

A reconstruction of cubic rs-ZnO on MgO (200) substrate through (100) plane of w-ZnO:rs-ZnO for transparent electronic application

Santosh M. Bobade

Appl. Phys. Lett. 100, 072102 (2012); http://dx.doi.org/10.1063/1.3680556 (4 pages) | Cited 2 times

Online Publication Date: 13 February 2012

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ZnO crystallizes in various crystallographic forms. While, the zinc blende (zb) and the rock salt (rs) structure of ZnO occur at high pressure, wurtzite (w) ZnO is the observed structure under ambient conditions. Interestingly, the high pressure polymorph of ZnO, cubic rs-ZnO oxide is presented on MgO (200) substrate at ordinary condition of temperature and pressure. The lattice constant of rs-ZnO is observed to be 4.203 Å identical to that for MgO. The possible configurational path for the hexagonal to cubic transformation is proposed. The compression of w-ZnO along c-axis, movement of Zn or O sub-lattice along [math10] direction and (110) plane appears to drive the transition. It has also been observed that rs-ZnO on MgO substrate is stable for certain maximum thickness (150 nm). It may be possible to stabilize the cubic phase at lower temperature and smaller thickness level.
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71.20.Nr Semiconductor compounds
62.50.-p High-pressure effects in solids and liquids
61.66.-f Structure of specific crystalline solids

A study of single-crystal silicon diodes integrated on flexible substrates using conductive adhesives

C. Doran, W. Chen, T. L. Alford, and S. S. Lau

Appl. Phys. Lett. 100, 072103 (2012); http://dx.doi.org/10.1063/1.3684970 (3 pages)

Online Publication Date: 13 February 2012

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In this study, we investigated the possibility of fabricating flexible single-crystal Si-Pd diodes on polymer substrates using silver-filled conductive tape or epoxy. This simple technique mitigates the complexity of process-intensive metal-bonding schemes to achieve backside electrical contacts on semiconductor devices. The performance of such devices is evaluated while bent to a 1.2 cm radius of curvature. The longer-term stability of the devices fabricated is also briefly discussed.
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85.30.Kk Junction diodes

Threading dislocation reduction in transit region of GaN terahertz Gunn diodes

Liang Li, Lin-An Yang, Jin-Cheng Zhang, Jun-Shuai Xue, Sheng-Rui Xu, Ling Lv, Yue Hao, and Mu-Tong Niu

Appl. Phys. Lett. 100, 072104 (2012); http://dx.doi.org/10.1063/1.3685468 (4 pages)

Online Publication Date: 14 February 2012

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An effect of the position of notch-doping layer in 1-μm GaN Gunn diode on threading dislocations (TDs) distribution is investigated by transmission electron microscopy. Compared with the top-notching-layer (TNL) structure, the bottom-notching-layer (BNL) structure can efficiently reduce the TDs density and improve the crystal quality in the transit region of GaN Gunn diode because it exhibits twice-transition of growth mode from atomic step flow to layer-by-layer nucleation and leads to a significant annihilation of TDs before penetrating into the transit region. X-ray diffraction and Raman spectroscopy reveal that the BNL structure has less compressive stress than the TNL structure.
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85.30.Tv Field effect devices

Electronic transport in doped mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films

L. R. Wienkes, C. Blackwell, and J. Kakalios

Appl. Phys. Lett. 100, 072105 (2012); http://dx.doi.org/10.1063/1.3685491 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2012

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We report observations of three distinct conduction mechanisms in n-type doped mixed-phase amorphous/nanocrystalline silicon thin films over a range of nanocrystallite concentrations and temperatures. As the temperature is varied from 470 to 10 K, we observe activated conduction, multiphonon hopping (MPH), and Mott variable range hopping (VRH) as the nanocrystal content is increased. The transition from MPH to Mott-VRH hopping around 50 K is tentatively ascribed to the freeze out of the phonon modes.
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73.61.Cw Elemental semiconductors
61.46.Hk Nanocrystals
63.20.kg Phonon-phonon interactions
72.20.Ee Mobility edges; hopping transport
73.50.Dn Low-field transport and mobility; piezoresistance

Electronic structure of ternary CdxZn1−xO (0 ≤ x ≤ 0.075) alloys

Henry Hung-Chun Lai, Vladimir L. Kuznetsov, Russell G. Egdell, and Peter P. Edwards

Appl. Phys. Lett. 100, 072106 (2012); http://dx.doi.org/10.1063/1.3684251 (4 pages) | Cited 1 time

Online Publication Date: 14 February 2012

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Narrowing of the electronic bandgap of ZnO by doping with cadmium opens up further potential uses of the material for photocatalytic applications. However, the mechanism of this important bandgap modification is still unclear. This letter demonstrates that for doped materials, the Fermi level resides within the bandgap in the bulk but lies above the conduction band minimum at the surface of the material, thus producing downward band bending and electron accumulation in the near surface region.
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71.20.Nr Semiconductor compounds
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
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)
78.40.Fy Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Molecular beam epitaxy of InAlN lattice-matched to GaN with homogeneous composition using ammonia as nitrogen source

Man Hoi Wong, Feng Wu, Christophe A. Hurni, Soojeong Choi, James S. Speck, and Umesh K. Mishra

Appl. Phys. Lett. 100, 072107 (2012); http://dx.doi.org/10.1063/1.3686922 (4 pages) | Cited 2 times

Online Publication Date: 17 February 2012

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InAlN lattice-matched to GaN was grown by molecular beam epitaxy (MBE) using ammonia as the nitrogen source. The alloy composition, growth conditions, and strain coherence of the InAlN were verified by high resolution x-ray diffraction ω-2θ scans and reciprocal space maps. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy of the InAlN revealed the absence of lateral composition modulation that was observed in the films grown by plasma-assisted MBE. InAlN/AlN/GaN high electron mobility transistors with smooth surfaces were fabricated with electron mobilities exceeding 1600 cm2/Vs and sheet resistances below 244 Ω/sq.
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68.55.ag Semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
85.30.Tv Field effect devices

p-f hybridization in the ferromagnetic semiconductor HoN

J. D. Brown, J. E. Downes, C. J. McMahon, B. C. C. Cowie, A. Tadich, L. Thomsen, J. H. Guo, and P. A. Glans

Appl. Phys. Lett. 100, 072108 (2012); http://dx.doi.org/10.1063/1.3687176 (4 pages) | Cited 1 time

Online Publication Date: 17 February 2012

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The electronic structure of thin film HoN has been studied using soft x-ray spectroscopy. The combination of soft x-ray emission, x-ray absorption, and photoemission techniques yields direct evidence for hybridization between the N 2p and the Ho 4f states, previously unseen in this or related rare earth nitride systems. The N 2p states extend up to 10 eV below the Fermi level to nearly twice the binding energy as previously believed. Optical spectroscopy yields a minimum direct gap of 1.48 eV. In light of these results, we identify HoN as a prime candidate for spin-diffusion and spintronics applications.
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71.20.Nr Semiconductor compounds
78.70.En X-ray emission spectra and fluorescence
78.66.Li Other semiconductors
75.50.Pp Magnetic semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.Dm X-ray absorption spectra

Multi-dimensional laser spectroscopy of exciton polaritons with spatial light modulators

P. Mai, B. Pressl, M. Sassermann, Z. Vörös, G. Weihs, C. Schneider, A. Löffler, S. Höfling, and A. Forchel

Appl. Phys. Lett. 100, 072109 (2012); http://dx.doi.org/10.1063/1.3687180 (3 pages)

Online Publication Date: 17 February 2012

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We describe an experimental system that allows one to easily access the dispersion curve of exciton-polaritons in a microcavity. Our approach is based on two spatial light modulators, one for changing the excitation angles (momenta), and the other for tuning the excitation wavelength. We show that with this setup, an arbitrary number of states can be excited accurately and that re-configuration of the excitation scheme can be done at high speed.
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42.62.Fi Laser spectroscopy
42.79.Hp Optical processors, correlators, and modulators
42.60.Fc Modulation, tuning, and mode locking

Counting statistics in an InAs nanowire quantum dot with a vertically coupled charge detector

T. Choi, T. Ihn, S. Schön, and K. Ensslin

Appl. Phys. Lett. 100, 072110 (2012); http://dx.doi.org/10.1063/1.3687198 (4 pages) | Cited 2 times

Online Publication Date: 17 February 2012

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A gate-defined quantum dot (QD) in an InAs nanowire is fabricated on top of a quantum point contact realized in a two-dimensional electron gas. The strong coupling between these two quantum devices is used to perform time-averaged as well as time-resolved charge detection experiments for electron flow through the quantum dot. We demonstrate that the Fano factor describing shot noise or time-correlations in single-electron transport depends in the theoretically expected way on the asymmetry of the tunneling barriers even in a regime where the thermal energy kBT is comparable to the single-particle level spacing in the dot.
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73.63.Kv Quantum dots
72.70.+m Noise processes and phenomena
73.40.Gk Tunneling
73.63.Nm Quantum wires
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Enhancing magnetic vacancies in semiconductors by strain

Erjun Kan, Fang Wu, Yuemei Zhang, Hongjun Xiang, Ruifeng Lu, Chuanyun Xiao, Kaiming Deng, and Haibin Su

Appl. Phys. Lett. 100, 072401 (2012); http://dx.doi.org/10.1063/1.3685488 (3 pages) | Cited 5 times

Online Publication Date: 13 February 2012

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Although cation-vacancies can induce localized magnetic moments in semiconductors, the collective magnetism is impeded by low vacancy concentration. To improve the vacancy concentration, we study the effect of external hydrostatic strain on the vacancy formation energy. Our first-principles calculations discover that vacancy formation energy is significantly reduced in ionic semiconductors with the monotonic volume contraction, while only slightly decreased in covalent semiconductors. Especially for ZnO, the equilibrium concentration of cation-vacancies has been improved by 109 times. We predicted that strain can be used to produce “d0 magnetism” in ionic semiconductors much easier in experiments.
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61.72.jd Vacancies
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Pp Magnetic semiconductors
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Anisotropic bimodal distribution of blocking temperature with multiferroic BiFeO3 epitaxial thin films

C. K. Safeer, M. Chamfrault, J. Allibe, C. Carretero, C. Deranlot, E. Jacquet, J.-F. Jacquot, M. Bibes, A. Barthélémy, B. Dieny, H. Béa, and V. Baltz

Appl. Phys. Lett. 100, 072402 (2012); http://dx.doi.org/10.1063/1.3684812 (4 pages) | Cited 3 times

Online Publication Date: 13 February 2012

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Controlling BiFeO3 (BFO)/ferromagnet (FM) interfacial coupling appears crucial for electrical control of spintronic devices using this multiferroic. Here, we analyse the magnetic behaviour of exchange-biased epitaxial-BiFeO3/FM bilayers with in-plane or out-of-plane magnetic anisotropies. We report bimodal distributions of blocking temperatures similar to those of polycrystalline-antiferromagnet (AF)/FM bilayers. The high-temperature contribution depends on the FM anisotropy direction and is likely related to thermally activated depinning of domain walls in the BiFeO3 single crystal film as opposed to thermally activated reversal of spins in AF grains for polycrystalline AF. In contrast, the low-temperature contribution weakly depends on the anisotropy direction, consistent with a spin-glass origin.
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75.85.+t Magnetoelectric effects, multiferroics
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Particle size dependent hysteresis loss in La0.7Ce0.3Fe11.6Si1.4C0.2 first‐order systems

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

Appl. Phys. Lett. 100, 072403 (2012); http://dx.doi.org/10.1063/1.3684244 (4 pages) | Cited 5 times

Online Publication Date: 14 February 2012

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Here, we report particle size dependent hysteresis loss in La0.7Ce0.3Fe11.6Si1.4C0.2. Hysteresis loss was getting smaller with reducing the particle size. The reduced ratio can be as high as ∼61% as the sample is ground from bulk into small particles (20‐50 μm). Such reduction can be ascribed to the notably increased surface area of sample and the partially removed internal strain and grain boundaries, other than nucleation factors and electronic band structure. Meanwhile, entropy change |ΔS| slightly decreases, but the effective refrigeration capacity shows an increase due to the notable reduction of hysteresis loss. Our investigations also reveal particle size limitation. When the size is below 10 μm (average ∼ 4 μm), the sample may lose its stability and the |ΔS| notably reduces.
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75.30.Sg Magnetocaloric effect, magnetic cooling
61.72.Mm Grain and twin boundaries
73.20.At Surface states, band structure, electron density of states
71.20.Ps Other inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials

Intrinsic electroresistance of Sm0.60Sr0.40MnO3 and Sm0.55Sr0.45MnO3

S. T. Mahmud, M. M. Saber, H. S. Alagoz, R. Bouveyron, J. Jung, and K. H. Chow

Appl. Phys. Lett. 100, 072404 (2012); http://dx.doi.org/10.1063/1.3687179 (4 pages) | Cited 2 times

Online Publication Date: 14 February 2012

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We report investigations of the intrinsic electroresistance of polycrystalline Sm0.60Sr0.40MnO3 and Sm0.55Sr0.45MnO3 that are synthesized in the same way. These experiments were carried out with excitation using short current pulses, and are analyzed with the goal of drastically reducing the contribution of Joule heating on the electroresistance. We find that the changes of the intrinsic electroresistance with the current density are much more significant in Sm0.60Sr0.40MnO3 compared to Sm0.55Sr0.45MnO3. These results are compared with other recent measurements of the electroresistance in the same compositions. The possible underlying mechanisms for our observed composition-dependent changes are also discussed.
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72.80.Sk Insulators

Controlling domain walls velocities in ferromagnetic ring-shaped nanowires

M. Negoita, T. J. Hayward, and D. A. Allwood

Appl. Phys. Lett. 100, 072405 (2012); http://dx.doi.org/10.1063/1.3685467 (5 pages)

Online Publication Date: 15 February 2012

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We demonstrate a method by which domain walls (DWs) in planar magnetic ring-shaped nanowires can be propagated controllably at arbitrarily low velocities by confining them to geometrically defined energy minima. Using this technique, we propagate domain walls around a ring-shaped nanowire at velocities as small as 0.6 mm/s, low enough to allow ultra-cold atoms to be transported in magnetic “traps” formed by the domain wall’s stray field. We also show how the frequency of an external applied rotating field can be used to determine the domain walls’ velocity and that the thermally activated depinning of the walls from defects ultimately limits the precision to which their motion can be controlled.
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75.60.Ch Domain walls and domain structure
81.07.Gf Nanowires
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Cd Fabrication of magnetic nanostructures
72.15.Gd Galvanomagnetic and other magnetotransport effects

Electrode band structure effects in thin MgO magnetic tunnel junctions

J. M. Teixeira, J. Ventura, M. P. Fernández-García, J. P. Araujo, J. B. Sousa, P. Wisniowski, and P. P. Freitas

Appl. Phys. Lett. 100, 072406 (2012); http://dx.doi.org/10.1063/1.3687200 (3 pages)

Online Publication Date: 15 February 2012

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In this study, we demonstrate that, beyond the standard magnon excitations, the electronic band structure of the electrodes plays a significant role on the low bias voltage window (0 < |V| < 0.4 V) of the tunnel magnetoresistance (TMR) in thin MgO-CoFeB junctions. The tunneling conductance in the parallel state presents a minimum at about ±0.35 and ±0.3 V for the negative and positive bias, respectively. The presence of this minimum indicates a related decrease in the TMR(V). These observations are explained by the electronic band structures of bcc-Fe and Co.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.20.At Surface states, band structure, electron density of states
75.30.Ds Spin waves

Chirality switching and propagation control of a vortex domain wall in ferromagnetic nanotubes

J. A. Otálora, J. A. López-López, P. Vargas, and P. Landeros

Appl. Phys. Lett. 100, 072407 (2012); http://dx.doi.org/10.1063/1.3687154 (4 pages) | Cited 6 times

Online Publication Date: 17 February 2012

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We propose a procedure to manipulate the chirality and propagation of a vortex domain wall in ferromagnetic nanotubes by applying magnetic field pulses. It is found that the chiral state of the vortex wall can be switched, provided that (1) the field amplitude is between two critical values, the so-called chiral field and the well-known Walker field, and (2) the pulse length is longer than a critical time, which is the time needed by the wall to overcome a local energy barrier. These key parameters are estimated for Permalloy nanotubes and range between a few miliTesla and some nanoseconds.
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75.60.Ch Domain walls and domain structure
81.07.De Nanotubes
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures

Fe/MgO/Fe (100) textured tunnel junctions exhibiting spin polarization features of single crystal junctions

A. Duluard, B. Negulescu, C. Bellouard, M. Hehn, D. Lacour, Y. Lu, G. Lengaigne, F. Montaigne, S. Robert, S. Suire, and C. Tiusan

Appl. Phys. Lett. 100, 072408 (2012); http://dx.doi.org/10.1063/1.3687174 (4 pages)

Online Publication Date: 17 February 2012

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Crystallographic and spin polarized transport properties of (100) textured and (100) epitaxial Fe/MgO/Fe magnetic tunnel junctions are compared. Strong similarities in the transport properties show that structural coherence and magnetic quality at the 25 nm grain scale in textured junctions are sufficient to issue signatures of the spin polarized transport specific to a single crystal junction. This demonstrates that the lateral coherence of the Bloch tunneling wave function is identically limited in both systems. Our analysis leads to model the textured tunnel junction as a juxtaposition of nanometer sized single crystal junctions, placed in parallel.
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72.25.Mk Spin transport through interfaces
75.76.+j Spin transport effects
73.40.Rw Metal-insulator-metal structures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness
75.70.Ak Magnetic properties of monolayers and thin films
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Code-division multiplexing for x-ray microcalorimeters

G. M. Stiehl, W. B. Doriese, J. W. Fowler, G. C. Hilton, K. D. Irwin, C. D. Reintsema, D. R. Schmidt, D. S. Swetz, J. N. Ullom, and L. R. Vale

Appl. Phys. Lett. 100, 072601 (2012); http://dx.doi.org/10.1063/1.3684807 (3 pages) | Cited 2 times

Online Publication Date: 13 February 2012

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We demonstrate the code-division multiplexing (CDM) readout of eight transition-edge sensor microcalorimeters. The energy resolution is 3.0 eV (full width at half-maximum) or better at 5.9 keV, with a best resolution of 2.3 eV and a mean of 2.6 eV over the seven modulated detectors. The flux-summing CDM system is described and compared with similar time-division multiplexing (TDM) readout. We show that the math multiplexing disadvantage associated with TDM is not present in CDM. This demonstration establishes CDM as both a simple route to higher performance in existing TDM microcalorimetric experiments and a long-term approach to reaching higher multiplexing factors.
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07.85.-m X- and γ-ray instruments
29.40.-n Radiation detectors

Experimental realization of superconducting quantum interference devices with topological insulator junctions

M. Veldhorst, C. G. Molenaar, X. L. Wang, H. Hilgenkamp, and A. Brinkman

Appl. Phys. Lett. 100, 072602 (2012); http://dx.doi.org/10.1063/1.3686150 (3 pages) | Cited 14 times

Online Publication Date: 16 February 2012

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We demonstrate topological insulator (Bi2Te3) dc SQUIDs, based on superconducting Nb leads coupled to nano-fabricated Nb-Bi2Te3-Nb Josephson junctions. The high reproducibility and controllability of the fabrication process allow the creation of dc SQUIDs with parameters that are in agreement with design values. Clear critical current modulation of both the junctions and the SQUID with applied magnetic fields have been observed. We show that the SQUIDs have a periodicity in the voltage-flux characteristic of Φ0 of relevance to the ongoing pursuit of realizing interferometers for the detection of Majorana fermions in superconductor—topological insulator structures.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.25.Sv Critical currents
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
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