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20 May 2013

Volume 102, Issue 20 (partial)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 203301 (2013); http://dx.doi.org/10.1063/1.4804595 (4 pages)

Michael Salinas and Marcus Halik
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Enhanced photon-generated carrier extraction from Si nanostructure under additional infrared light irradiation

Wei Yu, Yanmei Xu, Huimin Li, Jin Wang, Guangsheng Fu, and Wanbing Lu

Appl. Phys. Lett. 102, 201101 (2013); http://dx.doi.org/10.1063/1.4807281 (4 pages)

Online Publication Date: 20 May 2013

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Recombination and trapping effect in quantum dots are large barriers to efficient photon-generated carrier extraction. In this paper, Infrared (IR)-assisted carrier extraction in a Si/SiO2 multiple quantum well is demonstrated. Operated at reverse bias, enhanced photoresponse from 300 to 700 nm is observed. External quantum efficiency nearly 200% is obtained when both visible light and IR are added. The enhancement is attributed to potential modulation by photo-illumination. A theoretical model including three processes is presented to explain this conclusion. The secondary light source IR could excite trapped carriers from the defects at the Si/SiO2 interface, improving extraction efficiency.
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82.50.Hp Processes caused by visible and UV light

Dopant migration effects in terahertz quantum cascade lasers

C. Deutsch, H. Detz, M. Krall, M. Brandstetter, T. Zederbauer, A. M. Andrews, W. Schrenk, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 102, 201102 (2013); http://dx.doi.org/10.1063/1.4805040 (4 pages)

Online Publication Date: 20 May 2013

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We demonstrate that dopant migration and the resulting impurity scattering can strongly influence the performance of GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers. A nominally symmetric structure allows us to compare the negative and positive bias behavior of the very same device. Dopants, migrated towards the upper laser level during sample growth, degrade the lasing performance due to enhanced impurity scattering rates. The consequences are a higher threshold current (+30%) and reduced optical output power (–29%) in the affected operating direction. This polarity dependent performance is reversed in an asymmetrically doped sample, which imitates the migration of dopants against the growth direction.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.U- Doping and impurity implantation

Single InAs quantum dot coupled to different “environments” in one wafer for quantum photonics

Ying Yu, Xiang-Jun Shang, Mi-Feng Li, Guo-Wei Zha, Jian-Xing Xu, Li-Juan Wang, Guo-Wei Wang, Hai-Qiao Ni, Xiuming Dou, Baoquan Sun, and Zhi-Chuan Niu

Appl. Phys. Lett. 102, 201103 (2013); http://dx.doi.org/10.1063/1.4807502 (4 pages)

Online Publication Date: 20 May 2013

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Self assembled small InAs quantum dots (SQDs) were formed in various densities and environments using gradient InAs deposition on a non-rotating GaAs substrate. Two SQD environments (SQD I and SQD II) were characterized. SQD I featured SQDs surrounded by large QDs, and SQD II featured individual SQDs in the wetting layer (WL). Micro-photoluminescence of single QDs embedded in a cavity under various excitation powers and electric fields gave insight into carrier transport processes. Potential fluctuations of the WL in SQD II, induced by charge redistribution, show promise for charge-tunable QD devices; SQD I shows higher luminescence intensity as a single-photon source.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Kv Quantum dots
78.55.Cr III-V semiconductors

Generation of high-flux attosecond extreme ultraviolet continuum with a 10 TW laser

Y. Wu, E. Cunningham, H. Zang, J. Li, M. Chini, X. Wang, Y. Wang, K. Zhao, and Z. Chang

Appl. Phys. Lett. 102, 201104 (2013); http://dx.doi.org/10.1063/1.4807395 (4 pages)

Online Publication Date: 21 May 2013

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We report a laser system that delivers 15 fs pulses with 200 mJ energy at a 10 Hz repetition rate. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two-stage Ti:sapphire chirped-pulse power amplifier with sub-mJ white-light pulses from a gas-filled hollow-core fiber. With this laser, an extreme ultraviolet (XUV) super-continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The XUV pulse energy was ∼100 nJ at the exit of the argon gas target.
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42.65.-k Nonlinear optics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Wd Fiber lasers
42.60.-v Laser optical systems: design and operation
42.60.By Design of specific laser systems

Excitation power dependence of the Purcell effect in photonic crystal microcavity lasers with quantum wires

J. Canet-Ferrer, I. Prieto, G. Muñoz-Matutano, L. J. Martínez, L. E. Muñoz-Camuniez, J. M. Llorens, D. Fuster, B. Alén, Y. González, L. González, P. A. Postigo, and J. P. Martínez-Pastor

Appl. Phys. Lett. 102, 201105 (2013); http://dx.doi.org/10.1063/1.4807439 (4 pages)

Online Publication Date: 21 May 2013

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The Purcell effect dependence on the excitation power is studied in photonic crystal microcavity lasers embedding InAs/InP quantum wires. In the case of non-lasing modes, the Purcell effect has low dependence on the optical pumping, attributable to an exciton dynamics combining free and localized excitons. In the case of lasing modes, the influence of the stimulated emission makes ambiguous the determination of the Purcell factor. We have found that this ambiguity can be avoided by measuring the dependence of the decay time on the excitation power. These results provide insights in the determination of the Purcell factor in microcavity lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Parasitic nonlinearities in photon pair generation via integrated spontaneous four-wave mixing: Critical problem or distraction?

L. G. Helt, M. J. Steel, and J. E. Sipe

Appl. Phys. Lett. 102, 201106 (2013); http://dx.doi.org/10.1063/1.4807503 (5 pages)

Online Publication Date: 21 May 2013

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We consider integrated photon pair sources based on spontaneous four-wave mixing and derive expressions for the pump powers at which various nonlinear processes become relevant for a variety of source materials and structures. These expressions serve as rules of thumb in identifying reasonable parameter regimes for the design of such sources. We demonstrate that if pump powers are kept low enough to suppress cross-phase modulation, multi-pair events as well as many other nonlinear effects are often also constrained to negligible levels.
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42.50.-p Quantum optics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Stimulated Raman scattering cascade spanning the wavelength range of 523 to 1750 nm using a graded-index multimode optical fiber

Hamed Pourbeyram, Govind P. Agrawal, and Arash Mafi

Appl. Phys. Lett. 102, 201107 (2013); http://dx.doi.org/10.1063/1.4807620 (4 pages)

Online Publication Date: 21 May 2013

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We report on the generation of a Raman cascade spanning the wavelength range of 523 to 1750 nm wavelength range in a standard telecommunication graded-index multimode optical fiber. Despite the highly multimode nature of the pump, the Raman peaks are generated in specific modes of the fiber, confirming substantial beam cleanup during the stimulated Raman scattering process.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.81.Ht Gradient-index (GRIN) fiber devices

Two-photon nanolithography of positive photoresist thin film with ultrafast laser direct writing

Hong-Zhong Cao, Mei-Ling Zheng, Xian-Zi Dong, Feng Jin, Zhen-Sheng Zhao, and Xuan-Ming Duan

Appl. Phys. Lett. 102, 201108 (2013); http://dx.doi.org/10.1063/1.4807678 (4 pages)

Online Publication Date: 21 May 2013

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The authors investigate two-photon nanolithography of a positive photoresist thin film and the influence factor of spatial resolution. A spatial resolution of 85 nm, about one-ninth of the laser wavelength at 780 nm, has been realized by using commercial positive AZ P4620 photoresist. Theoretical analysis based on the exposure kinetics of photoactive compound of diazonaphthoquinone is consistent with experimental results. The trench's cross-section shape and spatial resolution are influenced by the standing wave interference caused by the incident and reflected light. This study would provide a protocol for fabricating micro/nanodevices by femtosecond laser direct writing of positive photoresists.
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81.16.Nd Micro- and nanolithography
68.55.aj Insulators
42.62.-b Laser applications
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Young-Lippmann equation revisited for nano-suspensions

Daniel Orejon, Khellil Sefiane, and Martin E. R. Shanahan

Appl. Phys. Lett. 102, 201601 (2013); http://dx.doi.org/10.1063/1.4807120 (3 pages)

Online Publication Date: 20 May 2013

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We present the results of an experimental study investigating electrowetting effects in nano-suspension drops. Wetting of sessile drops of titanium oxide (TiO2) nano-particles dispersed in deionised water was studied under a DC voltage potential. The presence of nano-particles is found to further enhance spreading of drops when a DC potential is applied. Results are explained based on the change in interfacial energy induced by nano-particle adsorption at the solid-liquid interface. An amendment of the Young-Lippmann equation accounting for the presence of nano-particles is proposed. The electrowetting expression proposed is validated against the experimental data for substrates with various dielectric thicknesses.
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82.70.Kj Emulsions and suspensions
68.08.Bc Wetting
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Fabrication and scanning tunneling microscopy characterization of suspended monolayer graphene on periodic Si nanopillars

Xin Zhao, Xiaofang Zhai, Aidi Zhao, Bing Wang, and J. G. Hou

Appl. Phys. Lett. 102, 201602 (2013); http://dx.doi.org/10.1063/1.4807139 (4 pages)

Online Publication Date: 20 May 2013

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We present the fabrication and scanning tunneling microscopy (STM) characterization of suspended monolayer graphene (SMG) on periodic Si nanostructure. Monolayer graphene (MG) was grown on Cu foils by chemical vapor deposition (CVD) and transferred onto a Si substrate with etched array of periodic nanopillars, obtaining partly suspended MG. Low-temperature STM characterization was performed on the suspension area of the MG with atomic resolution images obtained. The scanning tunneling spectroscopy of SMG shows a nonlinear behavior near the Fermi level (EF), which is attributed to the Dirac cone reshaped by electron-electron interaction.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.70.Kj Emulsions and suspensions
81.16.-c Methods of micro- and nanofabrication and processing

Investigation of the release of Si from SiO2 during the formation of manganese/ruthenium barrier layers

A. P. McCoy, P. Casey, J. Bogan, C. Byrne, and G. Hughes

Appl. Phys. Lett. 102, 201603 (2013); http://dx.doi.org/10.1063/1.4807428 (4 pages)

Online Publication Date: 20 May 2013

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The thermodynamic and structural stability of ruthenium-manganese diffusion barriers on SiO2 is assessed. A ∼2 nm film composed of partially oxidized manganese (MnOx where x < 1) was deposited on a 3 nm thick Ru film and the Mn-MnOx/Ru/SiO2 structure was subsequently thermally annealed. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy studies suggest the release and upward diffusion of Si from the dielectric substrate as a result of manganese-silicate formation at the Ru/SiO2 interface. The migration of Si up through the Ru film results in further manganese-silicate formation upon its interaction with the Mn-MnOx deposited layer.
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66.30.Ny Chemical interdiffusion; diffusion barriers
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Gh Other heat and thermomechanical treatments
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
65.40.G- Other thermodynamical quantities

Interfacial chemistry and valence band offset between GaN and Al2O3 studied by X-ray photoelectron spectroscopy

T. L. Duan, J. S. Pan, and D. S. Ang

Appl. Phys. Lett. 102, 201604 (2013); http://dx.doi.org/10.1063/1.4807736 (4 pages)

Online Publication Date: 21 May 2013

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The interface region between Ga-face n-type GaN and Al2O3 dielectric (achieved via atomic-layer deposition or ALD) is investigated by X-ray photoelectron spectroscopy (XPS). An increase in the Ga-O to Ga-N bond intensity ratio following Al2O3 deposition implies that the growth of an interfacial gallium sub-oxide (GaOx) layer occurred during the ALD process. This finding may be ascribed to GaN oxidation, which may still happen following the reduction of a thin native GaOx by trimethylaluminum (TMA) in the initial TMA-only cycles. The valence band offset between GaN and Al2O3, obtained using both core-level and valence band spectra, is found to vary with the thickness of the deposited Al2O3. This observation may be explained by an upward energy band bending at the GaN surface (due to the spontaneous polarization induced negative bound charge on the Ga-face GaN) and the intrinsic limitation of the XPS method for band offset determination.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
65.40.gp Surface energy
71.20.-b Electron density of states and band structure of crystalline solids
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.30.-b Specific chemical reactions; reaction mechanisms

Gold-titania interface toughening and thermal conductance enhancement using an organophosphonate nanolayer

Philippe K. Chow, Y. Cardona Quintero, Peter O'Brien, P. Hubert Mutin, Michael Lane, R. Ramprasad, and Ganpati Ramanath

Appl. Phys. Lett. 102, 201605 (2013); http://dx.doi.org/10.1063/1.4807436 (4 pages)

Online Publication Date: 21 May 2013

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We demonstrate that a mercaptan-terminated organophosphonate nanolayer at gold-titania interfaces can give rise to two- to three-fold enhancement in the interfacial fracture toughness and thermal conductance. Electron spectroscopy reveals that interfacial delamination occurs at the metal-molecule interface near the gold-sulfur bonds, consistent with density functional theory calculations of bond energies. Qualitative correlation between interfacial fracture toughness and bond energies suggest that organophosphonate nanolayers are resilient to humidity-induced degradation. These results, and the versatility of organophosphonates as surface functionalization agents for technologically relevant materials, unlock uncharted avenues for molecular engineering of interfaces in materials and devices for a variety of applications.
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73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
62.20.mm Fracture
61.50.Lt Crystal binding; cohesive energy

Large surface-enhanced Raman scattering from self-assembled gold nanosphere monolayers

Jake Fontana, John Livenere, Francisco J. Bezares, Joshua D. Caldwell, Ronald Rendell, and Banahalli R. Ratna

Appl. Phys. Lett. 102, 201606 (2013); http://dx.doi.org/10.1063/1.4807659 (5 pages)

Online Publication Date: 21 May 2013

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We demonstrate an average surface-enhanced Raman scattering enhancement on the order of 108 from benzenethiol molecules using self-assembled, macroscopic, and tunable gold nanosphere monolayers on non-templated substrates. The self-assembly of the nanosphere monolayers uses a simple and efficient technique that allows for the creation of a high-density, chemically functionalized gold nanosphere monolayers with enhancement factors comparable to those produced using top-down fabrication techniques. These films may provide an approach for the future development of portable chemical/biological sensors.
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78.66.Bz Metals and metallic alloys
81.16.Dn Self-assembly
68.55.at Other materials
78.30.Er Solid metals and alloys
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Experimental realization of reflection-type periodic diffraction correlation imaging

Hu Li, Yinzuo Zhang, Jianhong Shi, and Guihua Zeng

Appl. Phys. Lett. 102, 201901 (2013); http://dx.doi.org/10.1063/1.4807441 (4 pages)

Online Publication Date: 20 May 2013

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We demonstrate the periodic diffraction correlation imaging (PDCI) of a reflective object using only one array detector to achieve simpler setups of ghost imaging: no beam-splitter is needed, and only one detector is utilized. Multiple reference beams with a same pattern of the signal beam are generated in the PDCI, which makes PDCI realize high-order imaging more easily than conventional ghost imaging. Further, the influence of background noise on the imaging quality in PDCI can be reduced by the image merging technology proposed in this letter.
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42.30.Va Image forming and processing
42.79.Dj Gratings
85.60.Gz Photodetectors (including infrared and CCD detectors)

In-situ X-ray diffraction combined with scanning AC nanocalorimetry applied to a Fe0.84Ni0.16 thin-film sample

John M. Gregoire, Kechao Xiao, Patrick J. McCluskey, Darren Dale, Gayatri Cuddalorepatta, and Joost J. Vlassak

Appl. Phys. Lett. 102, 201902 (2013); http://dx.doi.org/10.1063/1.4806972 (4 pages)

Online Publication Date: 21 May 2013

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We combine the characterization techniques of scanning AC nanocalorimetry and x-ray diffraction to study phase transformations in complex materials system. Micromachined nanocalorimeters have excellent performance for high-temperature and high-scanning-rate calorimetry measurements. Time-resolved X-ray diffraction measurements during in-situ operation of these devices using synchrotron radiation provide unprecedented characterization of thermal and structural material properties. We apply this technique to a Fe0.84Ni0.16 thin-film sample that exhibits a martensitic transformation with over 350 K hysteresis, using an average heating rate of 85 K/s and cooling rate of 275 K/s. The apparatus includes an array of nanocalorimeters in an architecture designed for combinatorial studies.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
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All-optical measurement of vertical charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices

B. V. Olson, L. M. Murray, J. P. Prineas, M. E. Flatté, J. T. Olesberg, and T. F. Boggess

Appl. Phys. Lett. 102, 202101 (2013); http://dx.doi.org/10.1063/1.4807433 (4 pages)

Online Publication Date: 20 May 2013

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Time-resolved differential transmission measurements were used to investigate vertical charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices (T2SLs). By optically generating excess carriers near one end of the mid-wave T2SL and measuring the transit time to a thin, lower-bandgap T2SL at the other end, the time-of-flight of vertically diffusing carriers was measured. Through investigation of both unintentionally doped and p-type T2SLs, the vertical hole and electron diffusion coefficients were measured to be 0.04 ± 0.03 cm2/s and 4.7 ± 0.5 cm2/s, corresponding to vertical mobilities of 6 ± 5 cm2/Vs and 700 ± 80 cm2/Vs, respectively, at a temperature of 77 K.
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73.63.-b Electronic transport in nanoscale materials and structures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.47.D- Time resolved spectroscopy (>1 psec)
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Magnetic tunnel junctions with Al2O3 tunnel barriers prepared by atomic layer deposition

Xinfei Liu and Jing Shi

Appl. Phys. Lett. 102, 202401 (2013); http://dx.doi.org/10.1063/1.4807132 (4 pages)

Online Publication Date: 20 May 2013

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Uniform Al2O3 tunnel barriers are fabricated with atomic layer deposition. The tunneling magnetoresistance in optimized Al2O3-based magnetic tunnel junctions is studied as a function of temperature in comparison with SrTiO3-based tunnel devices having the same La0.7Sr0.3MnO3 and Co electrodes. The junction resistance peaks at the onset temperature of the tunneling magnetoresistance which lies below the metal-insulator transition temperature of the La0.7Sr0.3MnO3 film. These results suggest a lower interface metal-insulator and ferromagnetic ordering temperature.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Pq Other materials
71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Exchange-spring like magnetic behavior of the tetragonal Heusler compound Mn2FeGa as a candidate for spin-transfer torque

Teuta Gasi, Ajaya K. Nayak, Jürgen Winterlik, Vadim Ksenofontov, Peter Adler, Michael Nicklas, and Claudia Felser

Appl. Phys. Lett. 102, 202402 (2013); http://dx.doi.org/10.1063/1.4807427 (4 pages)

Online Publication Date: 20 May 2013

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We report structural, magnetic, and Mössbauer studies of the Heusler compound Mn2FeGa. Theoretical calculations predict that a tetragonal phase in Mn2FeGa could be an interesting candidate for spin torque transfer applications due to the presence of perpendicular magnetic anisotropy. Experimentally, we found that Mn2FeGa crystallizes in a tetragonal structure after annealing at low temperatures ( ≤ 400 °C), whereas, it becomes pseudocubic for higher annealing temperatures. The sample annealed at 400 °C shows a high Curie temperature of 650 K and a hard-magnetic behavior. We observed a nonsaturating and exchange-spring type of hysteresis loops, which indicates that the sample contains two different magnetic states. The Mössbauer measurements clearly support the structural and magnetic data. All these properties make the material a potential candidate for spintronic devices, especially in thin films with perpendicular magnetic anisotropy.
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75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.66.Dk Alloys

A micro-structured ion-implanted magnonic crystal

Björn Obry, Philipp Pirro, Thomas Brächer, Andrii V. Chumak, Julia Osten, Florin Ciubotaru, Alexander A. Serga, Jürgen Fassbender, and Burkard Hillebrands

Appl. Phys. Lett. 102, 202403 (2013); http://dx.doi.org/10.1063/1.4807721 (4 pages)

Online Publication Date: 21 May 2013

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We investigate spin-wave propagation in a microstructured magnonic-crystal waveguide fabricated by localized ion implantation. The irradiation caused a periodic variation in the saturation magnetization along the waveguide. As a consequence, the spin-wave transmission spectrum exhibits a set of frequency bands, where spin-wave propagation is suppressed. A weak modification of the saturation magnetization by 7% is sufficient to decrease the spin-wave transmission in the band gaps by a factor of 10. These results evidence the applicability of localized ion implantation for the fabrication of efficient micron- and nano-sized magnonic crystals for magnon spintronic applications.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.U- Doping and impurity implantation
61.80.-x Physical radiation effects, radiation damage

Simulations of magnetic hysteresis loops for dual layer recording media

T. J. Fal, M. L. Plumer, J. P. Whitehead, J. I. Mercer, J. van Ek, and K. Srinivasan

Appl. Phys. Lett. 102, 202404 (2013); http://dx.doi.org/10.1063/1.4807501 (4 pages)

Online Publication Date: 21 May 2013

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A Kinetic Monte-Carlo algorithm is applied to examine MH loops of dual-layer magnetic recording media at finite temperature and long time scales associated with typical experimental measurements. In contrast with standard micromagnetic simulations, which are limited to the ns-μs time regime, our approach allows for the direct calculation of magnetic configurations over periods from minutes to years. The model is used to fit anisotropy and coupling parameters to experimental data on exchange-coupled composite media which are shown to deviate significantly from standard micromagnetic results. Sensitivities of the loops to anisotropy, inter-layer exchange coupling, temperature, and sweep rate are examined.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Two-beam spin noise spectroscopy

Yuriy V. Pershin, Valeriy A. Slipko, Dibyendu Roy, and Nikolai A. Sinitsyn

Appl. Phys. Lett. 102, 202405 (2013); http://dx.doi.org/10.1063/1.4807011 (4 pages)

Online Publication Date: 21 May 2013

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We propose a method of two-beam spin noise spectroscopy to test the spin transport at equilibrium via analysis of correlations between time-shifted spin fluctuations at different space locations. This method allows one to determine the strength of spin-orbit interaction and spin relaxation time and separate spin noise of conducting electrons from the background noise of localized electrons. We formulate a theory of two-beam spin noise spectroscopy in semiconductor wires with Bychkov-Rashba spin-orbit interaction taking into account several possible spin relaxation channels and finite size of laser beams. Our theory predicts a peak shift with respect to the Larmor frequency to higher or lower frequencies depending on the strength of spin orbit interaction and distance between the beams. The two-beam spin noise spectroscopy could find applications in experimental studies of semiconductors, emergent materials, and many other systems.
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72.25.-b Spin polarized transport
75.30.Ds Spin waves
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Superconductor/ferromagnet heterostructures exhibit potential for significant reduction of hysteretic losses

Philipp Krüger, Francesco Grilli, Michal Vojenčiak, Victor M. R. Zermeño, Eduard Demencik, and Stefania Farinon

Appl. Phys. Lett. 102, 202601 (2013); http://dx.doi.org/10.1063/1.4807136 (4 pages)

Online Publication Date: 20 May 2013

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First experimental observations of the ferromagnetic shielding effect in high-Tc superconducting coated conductors were carried out. Experimental results were compared to simulations calling upon finite-element calculations based on the H-formulation of Maxwell equations to model superconducting strips with ferromagnetic shields. Samples of copper-stabilized coated conductors were electroplated with nickel shields and afterwards characterized. Both externally applied oscillating transverse magnetic fields as well as transport currents were studied. Having observed promising gains with respect to the reduction of ac losses in both cases, we further investigated the potential of ferromagnetic shielding. The numerical model was able to reproduce and also predict experimental results very well and will serve as an indispensable tool to determine the potential of soft ferromagnetic materials to significantly reduce hysteretic losses.
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74.72.-h Cuprate superconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Resonance enhancement of difference-frequency generation through localized surface plasmon excitation

Xu Fang, Shin Yaginuma, Wakana Kubo, and Takuo Tanaka

Appl. Phys. Lett. 102, 203101 (2013); http://dx.doi.org/10.1063/1.4807169 (4 pages)

Online Publication Date: 20 May 2013

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We report the experimental observation of difference-frequency generation in gold nanoparticles under localized surface plasmon excitation. A zero-delay peak is detected in the differential transmission signal for a gold nanoparticle film with a MgF2 overlayer, showing that the energy transfer from pump light to probe light through the difference-frequency generation is resonantly enhanced by the excitation. This peak of differential transmission decreases in strength with higher probe fluences. Both the enhancement and the power dependence of the difference-frequency generation are explained by modeling the localized surface plasmons as a nonlinear Lorentz resonator.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.66.Bz Metals and metallic alloys

Core-shell magnetic exchange model for Co3O4 nanowires

Lan Chen, Yurong Yang, and Xiangkang Meng

Appl. Phys. Lett. 102, 203102 (2013); http://dx.doi.org/10.1063/1.4807393 (5 pages)

Online Publication Date: 20 May 2013

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First-principles calculations are performed to investigate the magnetic properties of Co3O4 nanowires. A microscopic core-shell magnetic exchange model, including intra-core, intra-plane, core-shell (core-plane), and plane-plane (shell-shell) interactions, is proposed. The sign of magnetic exchange constants (ferromagnetic or antiferromagnetic coupling) for the four interactions is computed and discussed with respect to nanowire diameter. Competition between plane-plane and core-plane interactions is found in nanowire larger than 15.4 Å. The four magnetic interactions and their competition in the nanostructures give an explanation of exchange bias effect, two order temperatures, spin-glass behavior, and magnetic fingerprints found in core-shell structures experimentally.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Gf Nanowires
75.10.Nr Spin-glass and other random models
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