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16 Sep 2002

Volume 81, Issue 12, pp. 2145-2305

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Determination of thermal focal length and pumping radius in gain medium in laser-diode-pumped Nd:YVO4 lasers

Feng Song, Chaobo Zhang, Xin Ding, Jingjun Xu, Guangyin Zhang, Matthew Leigh, and Nasser Peyghambarian

Appl. Phys. Lett. 81, 2145 (2002); http://dx.doi.org/10.1063/1.1506789 (3 pages) | Cited 50 times

Online Publication Date: 9 September 2002

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A method to determine the focal length of a thermal lens and pumping laser beam waist in the gain medium in laser-diode-pumped solid-state lasers is presented. This method, using resonator transform circle theory, is both simple and reliable. The measured focal length of the thermal lens is used to calculate the beam waist of pumping laser inside the gain medium. The effect of the thermal lens on the output power is also measured and analyzed. © 2002 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems

Wide-field, real-time depth-resolved imaging using structured illumination with photorefractive holography

Z. Ansari, Y. Gu, J. Siegel, R. Jones, P. M. W. French, D. D. Nolte, and M. R. Melloch

Appl. Phys. Lett. 81, 2148 (2002); http://dx.doi.org/10.1063/1.1507354 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2002

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We have demonstrated real-time, wide-field depth-resolved imaging by combining the techniques of structured illumination and photorefractive holography. These proof of principle experiments illustrate the potential for providing real-time three-dimensional photorefractive holographic imaging with both reflected light and fluorescence. © 2002 American Institute of Physics.
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42.40.My Applications
87.57.N- Image analysis
42.30.Wb Image reconstruction; tomography
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Comparison of ultraviolet light-emitting diodes with peak emission at 340 nm grown on GaN substrate and sapphire

A. Yasan, R. McClintock, K. Mayes, S. R. Darvish, H. Zhang, P. Kung, M. Razeghi, S. K. Lee, and J. Y. Han

Appl. Phys. Lett. 81, 2151 (2002); http://dx.doi.org/10.1063/1.1508414 (3 pages) | Cited 22 times

Online Publication Date: 9 September 2002

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Based on AlInGaN/AlInGaN multiquantum wells, we compare properties of ultraviolet light-emitting diodes (LED) with peak emission at 340 nm grown on free-standing hydride vapor phase epitaxially grown GaN substrate and on sapphire. For the LED grown on GaN substrate, a differential resistance as low as 13 Ω and an output power of more than one order of magnitude higher than that of the same structure grown on sapphire are achieved. Due to higher thermal conductivity of GaN, output power of the LEDs saturates at higher injection currents compared to the devices grown on sapphire. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Fi Electroluminescence

Intrinsic nonlinearity of the light–current characteristic of semiconductor lasers with a quantum-confined active region

Levon V. Asryan, Serge Luryi, and Robert A. Suris

Appl. Phys. Lett. 81, 2154 (2002); http://dx.doi.org/10.1063/1.1508171 (3 pages) | Cited 9 times

Online Publication Date: 9 September 2002

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We describe a mechanism of nonlinearity of the light–current characteristic common to heterostructure lasers with a reduced-dimensionality active region. It arises from (i) noninstantaneous carrier capture into the active region and (ii) nonlinear (in the carrier density) recombination rate outside the active region. Because of (i), the carrier density outside the active region rises with injection current above threshold, and because of (ii), the useful fraction of current (that ends up as output light) decreases. We derive a universal closed-form expression for the internal differential quantum efficiency that holds true for quantum well, quantum wire, and quantum dot lasers. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.-k Nonlinear optics

Multiwatt average power continua generation in holey fibers pumped by kilowatt peak power seeded ytterbium fiber amplifier

P. A. Champert, S. V. Popov, M. A. Solodyankin, and J. R. Taylor

Appl. Phys. Lett. 81, 2157 (2002); http://dx.doi.org/10.1063/1.1508417 (3 pages) | Cited 4 times

Online Publication Date: 9 September 2002

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We demonstrate up to 3.8 W average power broad continuum generation in holey fibers pumped by a kilowatt peak, 10 W average power, single-mode, seeded ytterbium fiber amplifier at 1064 nm. Components of generated continua and spectral slicing indicate major contributions of Raman and Kerr nonlinearities. The proposed configuration opens the way to fully fiber integrated multiwatt white light sources. © 2002 American Institute of Physics.
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42.55.Wd Fiber lasers
78.45.+h Stimulated emission
42.60.By Design of specific laser systems
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Single spin states in a defect center resolved by optical spectroscopy

F. Jelezko, I. Popa, A. Gruber, C. Tietz, J. Wrachtrup, A. Nizovtsev, and S. Kilin

Appl. Phys. Lett. 81, 2160 (2002); http://dx.doi.org/10.1063/1.1507838 (3 pages) | Cited 75 times

Online Publication Date: 9 September 2002

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Individual paramagnetic defect centers in diamond nanocrystals have been investigated by low-temperature high-resolution optical spectroscopy. Narrow fluorescence excitation spectral lines have been found, indicating transitions between individual spin sublevels. Spectral diffusion is explained by cross relaxation among spin sublevels and by the presence of excited electrons in the conduction band of diamond. The relaxation times are in the millisecond range. The system may be useful for quantum information processing with individual electron spins. © 2002 American Institute of Physics.
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78.40.Fy Semiconductors
71.55.Cn Elemental semiconductors
78.55.Ap Elemental semiconductors
76.30.Mi Color centers and other defects
03.67.Lx Quantum computation architectures and implementations

Gain-maximized GaAs/AlGaAs quantum-cascade laser with digitally graded active region

D. Indjin, S. Tomić, Z. Ikonić, P. Harrison, R. W. Kelsall, V. Milanović, and S. Kočinac

Appl. Phys. Lett. 81, 2163 (2002); http://dx.doi.org/10.1063/1.1508166 (3 pages) | Cited 10 times

Online Publication Date: 9 September 2002

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An advanced strategy for the optimal design and realization of a GaAs/AlGaAs quantum-cascade laser is presented. It relies on recently established inverse scattering techniques to design an optimal smooth active region profile, followed by a conversion to an almost equivalent digitally graded structure, comprising just two different alloy compositions. In order to compare the output characteristics of optimized and previously realized structures, the intersubband electron scattering transport in quantum cascade lasers is analyzed. A full self-consistent rate equation model which includes all relevant electron-longitudinal optical phonon and electron–electron scattering mechanisms between injector/collector, active region, and continuumlike states is employed. Whilst the gain coefficients and threshold currents calculated at 77 and 300 K for the structure with a standard triple quantum well active region show excellent agreement with recent experiments, a significant improvement of these parameters is predicted for the optimized digitally graded quantum-cascade laser. © 2002 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells

Demonstration of reverse symmetry waveguide sensing in aqueous solutions

Róbert Horváth, Henrik C. Pedersen, and Niels B. Larsen

Appl. Phys. Lett. 81, 2166 (2002); http://dx.doi.org/10.1063/1.1508814 (3 pages) | Cited 32 times

Online Publication Date: 9 September 2002

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A reverse symmetry waveguide is presented for evanescent wave sensing in aqueous solutions. The waveguide consists of a thin polystyrene film, supported by a thicker substrate layer of nanoporous silica on glass. The nanoporous substrate layer has a refractive index of nS = 1.193, hence, with an aqueous cover refractive index of nC = 1.331, a reverse symmetry (nS<nC) is obtained. A surface relief grating formed in the polystyrene film is used as a coupling element. Sensitivities considerably higher than for a conventional waveguide sensor are demonstrated. © 2002 American Institute of Physics.
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42.81.Pa Sensors, gyros
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings

Ultrafast frequency-selective optical switching based on thin self-assembled organic chromophoric films with a large second-order nonlinear response

Gang Wang, Peiwang Zhu, Tobin J. Marks, and J. B. Ketterson

Appl. Phys. Lett. 81, 2169 (2002); http://dx.doi.org/10.1063/1.1506413 (3 pages) | Cited 5 times

Online Publication Date: 9 September 2002

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Thin films consisting of self-assembled chromophoric superlattices exhibit very large second-order nonlinear responses [χ(2)]. Using such films, a “static” diffraction grating is created by the interference of two coherent infrared beams from a pulsed yttritium–aluminum–garnet laser. This grating is used to switch the second-harmonic and third-harmonic “signal” beams (generated from the fundamental “pump” beam or mixed within the chromophoric superlattice) into different channels (directions). Ultrafast switching response as a function of the time overlap of the pumping beams is demonstrated. It is suggested that such devices can be used to spatially and temporally separate signal trains consisting of pulses having different frequencies and arrival times. © 2002 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Jk Polymers and organics
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Wc Optical coatings
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Effect of MgZnO-layer capping on optical properties of ZnO epitaxial layers

T. Makino, K. Tamura, C. H. Chia, Y. Segawa, M. Kawasaki, A. Ohtomo, and H. Koinuma

Appl. Phys. Lett. 81, 2172 (2002); http://dx.doi.org/10.1063/1.1506783 (3 pages) | Cited 20 times

Online Publication Date: 9 September 2002

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Photoluminescence (PL) and reflectivity spectra of ZnO epilayers capped with MgxZn1−xO layers (up to x = 0.36) are reported. These capped films were epitaxially grown on lattice-matched ScAlMgO4 substrates by laser molecular-beam epitaxy. A photoluminescence spectrum from the ZnO layer taken at 5 K shows emission bands at 3.389, 3.376, and 3.362 eV. The two higher bands are due to A- and B-free exciton emissions and the lowest band is due to emission of a neutral-acceptor bound exciton (I6). The linewidth of the I6 emission in our uncapped sample (0.8 meV) is significantly smaller than that in the capped one (6 meV). This is probably due to strain applied across the ZnO layer because of the difference in lattice constant between the two layers. The spectral assignment of the free exciton emissions is strengthened by a comparison with a temperature-dependent PL study and a reflectivity study. With an increase in temperature, the intensity of the bound exciton emission line decreased drastically and became comparable to that of free exciton lines. Free exciton emissions are already detectable at the liquid He temperature for the capped samples, which is never achieved in the uncapped ones grown under identical conditions. This indicates the high degree of purity of the capped films. © 2002 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Fg Pulsed laser ablation deposition
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Infrared dielectric response function of strained In1−xGaxAs/InP epilayers

G. Yu, N. L. Rowell, D. J. Lockwood, and P. J. Poole

Appl. Phys. Lett. 81, 2175 (2002); http://dx.doi.org/10.1063/1.1506006 (3 pages) | Cited 11 times

Online Publication Date: 9 September 2002

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Polarized infrared reflectivity measurements have been performed on strained In1−xGaxAs epilayers grown by chemical beam epitaxy on semi-insulating InP(100) with x varied from 0.314 to 0.556. Fitting of the reflectance spectra yielded excellent agreement with three longitudinal and transverse optical phonon pairs, corresponding to GaAs-like, disorder-induced, and InAs-like modes. The dielectric response function and phonon frequency dependences for all modes were obtained versus Ga fraction. © 2002 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Properties of AlxGa1−xN layers grown by plasma-assisted molecular-beam epitaxy under Ga-rich conditions

L. He, M. A. Reshchikov, F. Yun, D. Huang, T. King, and H. Morkoç

Appl. Phys. Lett. 81, 2178 (2002); http://dx.doi.org/10.1063/1.1506206 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2002

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AlxGa1−xN films were grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire substrates under Ga-rich conditions. To control the AlxGa1−xN composition over the entire range, the Al and Ga arrival rates were fixed while the nitrogen arrival rate was varied. We have found that the Al fraction increased with decreasing N flow due to preferentially favorable bonding of Al and N over Ga and N. Consequently, the growth rate decreased as the Al mole fraction increased. A photoluminescence quantum efficiency at 15 K was markedly higher for the AlxGa1−xN layers grown under Ga-rich conditions (3%–48%) compared to the layers grown under N-rich conditions (1%–10%), indicating much reduced nonradiative recombination in samples grown under Ga-rich conditions. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
68.55.-a Thin film structure and morphology
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Growth of SiCAlN on Si(111) via a crystalline oxide interface

John Tolle, R. Roucka, P. A. Crozier, A. V. G Chizmeshya, I. S. T. Tsong, and J. Kouvetakis

Appl. Phys. Lett. 81, 2181 (2002); http://dx.doi.org/10.1063/1.1507358 (3 pages) | Cited 3 times

Online Publication Date: 9 September 2002

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Growth of single-phase SiCAlN epitaxial films with the 2H–wurtzite structure is conducted directly on Si(111) despite the structural differences and large lattice mismatch (19%) between the two materials. Commensurate heteroepitaxy is facilitated by the conversion of native and thermally grown SiO2 layers on Si(111) into crystalline oxides by in situ reactions of the layers with Al atoms and the H3SiCN precursor, forming coherent interfaces with the Si substrate and the film. High-resolution transmission electron microscopy and electron energy-loss spectroscopy show that the amorphous SiO2 films are entirely transformed into a crystalline Si–Al–O–N framework in registry with the Si(111) surface. This crystalline interface acts as a template for nucleation and growth of epitaxial SiCAlN. Integration of wide-band-gap semiconductors with Si is readily achieved by this process. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy

Determination of recombination parameters of phosphors from cathodoluminescent characteristics

Sergey A. Bukesov and Duk Y. Jeon

Appl. Phys. Lett. 81, 2184 (2002); http://dx.doi.org/10.1063/1.1508170 (3 pages) | Cited 7 times

Online Publication Date: 9 September 2002

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A simple method to determine recombination parameters of polycrystalline phosphor materials is proposed based on a comparison of a theoretical prediction of cathodoluminescent intensity with experimental characteristics. The obtained parameters are very sensitive to additional treatments of phosphor surface, especially to chemical modification by even small amounts of inorganic oxides. The proposed method offers a simple and rapid way of controlling recombination parameters of luminescent materials. © 2002 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena

Light-induced assembly of tailored droplet arrays in nematic emulsions

Takahiro Yamamoto, Jun Yamamoto, Bohdan I. Lev, and Hiroshi Yokoyama

Appl. Phys. Lett. 81, 2187 (2002); http://dx.doi.org/10.1063/1.1508816 (3 pages) | Cited 17 times

Online Publication Date: 9 September 2002

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Dynamic manipulation of droplets could be achieved by light in a nematic liquid crystal (LC) doped with photochromic azobenzene derivatives. On irradiation of ultraviolet light, the trans→cis photoisomerization drives a directional motion of the droplets towards the cis-rich region and assembled close-packed two-dimensional hexagonal colloidal crystals. This behavior is mainly attributable to the reduction of the droplet-LC interfacial tension, associated with the enhanced surface activity of cis isomers. We also performed photochemical assembly of tailored droplet arrays by projection of computer-generated images on the samples. The photoinduced manipulation of droplets will provide a versatile approach to microstructuring of LC devices. © 2002 American Institute of Physics.
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82.70.Kj Emulsions and suspensions
82.30.Qt Isomerization and rearrangement
82.50.-m Photochemistry
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
42.70.Df Liquid crystals
61.30.-v Liquid crystals

High-quality SiO2 film formation by highly concentrated ozone gas at below 600 °C

Tetsuya Nishiguchi, Hidehiko Nonaka, Shingo Ichimura, Yoshiki Morikawa, Mitsuru Kekura, and Masaharu Miyamoto

Appl. Phys. Lett. 81, 2190 (2002); http://dx.doi.org/10.1063/1.1507829 (3 pages) | Cited 22 times

Online Publication Date: 9 September 2002

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Highly concentrated (>93 vol %) ozone (O3) gas was used to oxidize silicon for obtaining high-quality SiO2 film at low temperature. Compared to O2 oxidation, more than 500 °C lower temperature oxidation (i.e., from 830 to 330 °C) has been enabled for achieving the same SiO2 growth rate. A 6 nm SiO2 film, for example, could be grown at 600 °C within 3 min at 900 Pa O3 atmosphere. The temperature dependence of the oxidation rate is relatively low, giving an activation energy for the parabolic rate constant of 0.32 eV. Furthermore, a 400 °C grown SiO2 film was found to have satisfactory electrical properties with a small interface trap density (5×1010 cm−2/eV) and large breakdown field (14 MV/cm). © 2002 American Institute of Physics.
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81.65.Mq Oxidation
73.61.Ng Insulators
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Growth and characterization of single-crystal GaN nanorods by hydride vapor phase epitaxy

Hwa-Mok Kim, D. S. Kim, D. Y. Kim, T. W. Kang, Yong-Hoon Cho, and K. S. Chung

Appl. Phys. Lett. 81, 2193 (2002); http://dx.doi.org/10.1063/1.1507617 (3 pages) | Cited 62 times

Online Publication Date: 9 September 2002

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Single-crystalline GaN nanorods are formed on a sapphire substrate by hydride vapor phase epitaxy (HVPE). Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and cathodoluminescence (CL) techniques. The high density of straight and well-aligned nanorods with a diameter of 80–120 nm formed uniformly over the entire 2 in. sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the formed GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. We observed a higher CL peak position of individual GaN nanorods than that of bulk GaN as well as a blueshift of CL peak position with decreasing the diameter of GaN nanorods, which are attributed to quantum confinement effect in one-dimensional GaN nanorods. We demonstrate that the well-aligned, single-crystalline GaN nanorods with high density, high crystal quality, and good spatial uniformity are formed by the HVPE method. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.60.Hk Cathodoluminescence, ionoluminescence

Tunable laser spectroscopy of spin injection in ZnMnSe/ZnCdSe quantum structures

I. A. Buyanova, I. G. Ivanov, B. Monemar, W. M. Chen, A. A. Toropov, Ya. V. Terent’ev, S. V. Sorokin, A. V. Lebedev, S. V. Ivanov, and P. S. Kop’ev

Appl. Phys. Lett. 81, 2196 (2002); http://dx.doi.org/10.1063/1.1508162 (3 pages) | Cited 20 times

Online Publication Date: 9 September 2002

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Magneto-optical spectroscopy in combination with tunable laser excitation is employed to study exciton spin alignment and injection in ZnMnSe/ZnCdSe quantum structures. This approach enables us to selectively create preferred spin orientation and to separately monitor subsequent spin injection from individual spin states, thus shedding light on a possible source of spin loss. It is shown that the limited spin polarization in a nonmagnetic quantum well due to spin injection from a ZnMnSe-based diluted magnetic semiconductor (DMS) is not caused by a limited degree of spin alignment in the DMS, which is in fact complete, but rather occurs during subsequent processes. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
78.67.De Quantum wells
73.21.Fg Quantum wells
78.55.Et II-VI semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
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Superconducting properties of MgB2 thin films prepared on flexible plastic substrates

Peter Kúš, Andrej Plecenik, Leonid Satrapinsky, Ying Xu, and Roman Sobolewski

Appl. Phys. Lett. 81, 2199 (2002); http://dx.doi.org/10.1063/1.1507828 (3 pages) | Cited 14 times

Online Publication Date: 9 September 2002

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Superconducting MgB2 thin films were prepared on 50-μm-thick, flexible polyamide Kapton-E foils by vacuum co-deposition of Mg and B precursors with nominal thickness of about 100 nm and a subsequent ex situ rapid annealing process in an Ar or vacuum atmosphere. In the optimal annealing process, the Mg–B films were heated to approximately 600 °C, but, at the same time, the backside of the structures was attached to a water-cooled radiator to avoid overheating of the plastic substrate. The resulting MgB2 films were amorphous with the onset of the superconducting transition at Tc,on ≈ 29 K and a transition width of approximately 3 K. The critical current density was >7×105 A/cm2 at 4.2 K, and its temperature dependence indicated a granular film composition with a network of intergranular weak links. The films could be deposited on large-area foils (up to 400 cm2) and, after processing, cut into any shape (e.g., strips) with scissors, or bent multiple times, without any observed degradation of their superconducting properties. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Batch-fabricated spin-injection magnetic switches

J. Z. Sun, D. J. Monsma, D. W. Abraham, M. J. Rooks, and R. H. Koch

Appl. Phys. Lett. 81, 2202 (2002); http://dx.doi.org/10.1063/1.1506794 (3 pages) | Cited 96 times

Online Publication Date: 9 September 2002

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A method is developed for the fabrication of sub-100 nm current-perpendicular spin-valve junctions with low contact resistance. The approach is to use a batch-fabricated trilayer template with the junction features defined by a metal stencil layer and an undercut in the insulator. The spin-valve thin film stack is deposited afterwards into the stencil, with the insulator undercut providing the necessary magnetic isolation. Using this approach, reproducible spin-current-induced magnetic switching is demonstrated for junctions down to 50 nm×100 nm in size. © 2002 American Institute of Physics.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Mk Spin transport through interfaces
75.47.De Giant magnetoresistance
75.60.Jk Magnetization reversal mechanisms

Detection of coherent and incoherent spin dynamics during the magnetic switching process using vector-resolved nonlinear magneto-optics

T. J. Silva, P. Kabos, and M. R. Pufall

Appl. Phys. Lett. 81, 2205 (2002); http://dx.doi.org/10.1063/1.1508163 (3 pages) | Cited 27 times

Online Publication Date: 9 September 2002

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It is usually assumed that magnetic switching proceeds via coherent rotation under conditions of high symmetry. There is no a priori reason to expect an inhomogeneous response when a uniform magnetic torque is applied to a homogeneous ferromagnet. We test this assumption using vector- and time-resolved nonlinear magneto-optic measurements on a continuous Ni–Fe film. While coherent dynamics are observed when the magnetization M is initially oriented along the easy axis (the preferred axis of M in the absence of external fields), we find evidence for inhomogeneous spin dynamics when M is initially oriented perpendicular to the easy axis, which suggests the generation of incoherent spin waves during the magnetic reorientation process. The inhomogeneity is sufficient to reduce the spatially averaged magnetic moment within the measured area by almost 50%.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Ds Spin waves
75.30.Cr Saturation moments and magnetic susceptibilities
78.66.Bz Metals and metallic alloys
78.47.-p Spectroscopy of solid state dynamics

Dependence of physical properties and giant magnetoresistance ratio on substrate position during rf sputtering of NiO and α-Fe2O3 for bottom spin valves

Seongtae Bae, Jack H. Judy, P. J. Chen, and W. F. Egelhoff

Appl. Phys. Lett. 81, 2208 (2002); http://dx.doi.org/10.1063/1.1508161 (3 pages) | Cited 2 times

Online Publication Date: 9 September 2002

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The dependence of composition, crystalline orientation texture, surface roughness, and giant magnetoresistance (GMR) ratio on substrate position during rf reactive sputtering of antiferromagnetic NiO and α-Fe2O3 films for dc magnetron sputtered Co/Cu/Co bottom spin valves have been investigated. For substrate positions from the center to edge of the target, the GMR ratio increased from 13.5% to 19.8% for NiO and from 9.8% to 13% for α-Fe2O3. These significant enhancements of GMR ratio was found to correlate with a decrease of surface roughness, increase in crystalline texture, and a nearly bulk stoichiometry of the NiO and α-Fe2O3 thin films. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Ee Antiferromagnetics
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
68.35.B- Structure of clean surfaces (and surface reconstruction)

Detection of a micron-sized magnetic sphere using a ring-shaped anisotropic magnetoresistance-based sensor: A model for a magnetoresistance-based biosensor

M. M. Miller, G. A. Prinz, S.-F. Cheng, and S. Bounnak

Appl. Phys. Lett. 81, 2211 (2002); http://dx.doi.org/10.1063/1.1507832 (3 pages) | Cited 120 times

Online Publication Date: 9 September 2002

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We have fabricated micron-sized NiFe ring-shaped sensors that show localized detection of the radial component of the dipolar fringing field from a single, partially magnetized, micron-sized NiFe sphere. Specifically, the anisotropic magnetoresistance response to this fringing field is strongly peaked when the sphere is directly above the center of the ring and rapidly decreases to zero when the sphere is outside the ring. Such a device is a model system for a proposed biosensor array architecture that could operate similarly to high-density random access computer memory.
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85.75.Ss Magnetic field sensors using spin polarized transport
87.80.-y Biophysical techniques (research methods)
75.47.De Giant magnetoresistance
85.75.Bb Magnetic memory using giant magnetoresistance

Reduced temperature and bias-voltage dependence of the magnetoresistance in magnetic tunnel junctions with Hf-inserted Al2O3 barrier

Byong Guk Park and Taek Dong Lee

Appl. Phys. Lett. 81, 2214 (2002); http://dx.doi.org/10.1063/1.1508413 (3 pages) | Cited 8 times

Online Publication Date: 9 September 2002

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A modified tunnel barrier structure for the magnetic tunnel junction (MTJ) was fabricated by inserting a Hf layer in the middle of the Al2O3 tunnel barrier. MTJs with the Hf-inserted barrier show a higher tunnel mangnetoresistance (TMR) ratio and weaker temperature and bias-voltage dependence of TMR compared to the MTJs with a conventional Al2O3 barrier. The enhancement of the TMR ratio and the reduction of the temperature and bias-voltage dependence were attributed to the reduction of defects in the barrier. © 2002 American Institute of Physics.
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73.40.Gk Tunneling
75.45.+j Macroscopic quantum phenomena in magnetic systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
72.15.Gd Galvanomagnetic and other magnetotransport effects

Monte Carlo simulation on the indirect exchange interactions of Co-doped ZnO film

Abraham F. Jalbout, Hanning Chen, and Scott L. Whittenburg

Appl. Phys. Lett. 81, 2217 (2002); http://dx.doi.org/10.1063/1.1508168 (3 pages) | Cited 42 times

Online Publication Date: 9 September 2002

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Monte Carlo simulations using a three-dimensional lattice model studied the Ruderman–Kittel–Kasuya–Yosida (RKKY) indirect exchange interaction of doped magnetic Co ions in ZnO films. The results of the calculations show that the RKKY interaction in Co-doped ZnO is long ranged and its magnitude is proportional to R−1 (inverse of the distance R from a central Co2+ ion). The sign oscillates with a frequency that depends on the concentration of the carrier. The long-distance sum of the RKKY indirect exchange energies is positive indicating that these materials are ferromagnetic, in direct correlation with previously reported results. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
75.40.Mg Numerical simulation studies
75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
75.70.Ak Magnetic properties of monolayers and thin films
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