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17 Jan 2005

Volume 86, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 033101 (2005); http://dx.doi.org/10.1063/1.1851002 (3 pages)

Kun Chen, Allen Taflove, Young L. Kim, and Vadim Backman
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Optical properties of InAs/GaAs surface quantum dots

Z. L. Miao, Y. W. Zhang, S. J. Chua, Y. H. Chye, P. Chen, and S. Tripathy

Appl. Phys. Lett. 86, 031914 (2005); http://dx.doi.org/10.1063/1.1854199 (3 pages) | Cited 23 times

Online Publication Date: 13 January 2005

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We report long-wavelength photoluminescence emission ( ∼ 1.6–1.7 μm) from self-organized InAs surface quantum dots (SQDs) grown on GaAs substrate without any capping layers. Photoluminescence (PL) properties of these quantum dots (QDs) are strongly affected by the surface states and strain relaxation mechanism. Compared to the case of capped InAs QDs, a large redshift of about 466 nm observed in the PL spectrum of SQDs can be attributed to the strain relaxation and the strong coupling of the confined states with the surface states. The PL properties of these SQDs can also be influenced by the presence of quasi-infinite surface potential.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots
78.68.+m Optical properties of surfaces
68.65.Hb Quantum dots (patterned in quantum wells)
73.20.At Surface states, band structure, electron density of states
68.35.Gy Mechanical properties; surface strains
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Effect of growth polarity on vacancy defect and impurity incorporation in dislocation-free GaN

F. Tuomisto, K. Saarinen, B. Lucznik, I. Grzegory, H. Teisseyre, T. Suski, S. Porowski, P. R. Hageman, and J. Likonen

Appl. Phys. Lett. 86, 031915 (2005); http://dx.doi.org/10.1063/1.1854745 (3 pages) | Cited 29 times

Online Publication Date: 13 January 2005

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We have used positron annihilation, secondary ion mass spectrometry, and photoluminescence to study the point defects in GaN grown by hydride vapor phase epitaxy (HVPE) on GaN bulk crystals. The results show that N polar growth incorporates many more donor and acceptor type impurities and also Ga vacancies. Vacancy clusters with a positron lifetime τD = 470±50 ps were found near the N polar surfaces of both the HVPE GaN layers and bulk crystals.
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81.05.Ea III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
78.66.Fd III-V semiconductors
78.70.Bj Positron annihilation
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Enhanced room-temperature luminescence efficiency through carrier localization in AlxGa1−xN alloys

C. J. Collins, A. V. Sampath, G. A. Garrett, W. L. Sarney, H. Shen, M. Wraback, A. Yu. Nikiforov, G. S. Cargill, and V. Dierolf

Appl. Phys. Lett. 86, 031916 (2005); http://dx.doi.org/10.1063/1.1856702 (3 pages) | Cited 29 times

Online Publication Date: 14 January 2005

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AlGaN samples grown by plasma-assisted molecular-beam epitaxy on sapphire (0001) substrates, with 20%–50% Al content and without the use of indium, show intense room-temperature photoluminescence that is significantly redshifted, 200–400 meV, from band edge. This intense emission is characterized by a long room-temperature lifetime ( ∼ 375 ps) comparable to that seen in low defect density ( ∼ 108 cm−2) GaN. Room-temperature monochromatic cathodoluminescence images at the redshifted peak reveal spatially nonuniform emission similar to that observed in In(Al)GaN alloys and attributed to compositional inhomogeneity. These observations suggest that spatial localization enhances the luminescence efficiency despite the high defect density (>1010 cm−2) of the films by inhibiting movement of carriers to nonradiative sites.
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78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Angle-dispersive neutron diffraction under high pressure to 10 GPa

S. Klotz, Th. Strässle, G. Rousse, G. Hamel, and V. Pomjakushin

Appl. Phys. Lett. 86, 031917 (2005); http://dx.doi.org/10.1063/1.1855419 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2005

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We present a method which allows high-quality powder neutron diffraction patterns to be obtained under pressure by angle-dispersive diffraction to at least 10 GPa. This technique uses a new type of Paris–Edinburgh press in conjunction with sintered boron nitride anvils. As an example, we show NiO diffraction patterns obtained under purely hydrostatic pressures up to 10 GPa. These data were collected within a few hours, and are free from any contaminating signal from the pressure cell. High-resolution nuclear and magnetic structural information can be readily extracted by Rietveld refinements, without additional data correction. This technique will allow powder neutron diffraction at elevated pressures to become a standard tool on continuous neutron facilities.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.43.Gt Powders, porous materials
62.50.-p High-pressure effects in solids and liquids
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
61.05.fm Neutron diffraction
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Corner overgrowth: Bending a high mobility two-dimensional electron system by 90°

M. Grayson, D. Schuh, M. Huber, M. Bichler, and G. Abstreiter

Appl. Phys. Lett. 86, 032101 (2005); http://dx.doi.org/10.1063/1.1851010 (3 pages) | Cited 14 times

Online Publication Date: 7 January 2005

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Introducing an epitaxial growth technique called corner overgrowth, we fabricate a quantum confinement structure consisting of a high-mobility GaAs/AlGaAs heterojunction overgrown on top of an ex situ cleaved substrate corner. The resulting corner-junction quantum-well heterostructure effectively bends a two-dimensional electron system (2DES) at an atomically sharp 90° angle. The high-mobility 2DES demonstrates fractional quantum Hall effect on both facets. Lossless edge-channel conduction over the corner confirms a continuum of 2D electrons across the junction, consistent with Hartree calculations of the electron distribution. This growth technique differs distinctly from cleaved-edge overgrowth and enables a complementary class of embedded quantum heterostructures.
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81.07.St Quantum wells
73.63.Hs Quantum wells
68.65.Fg Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Electrical properties of polycrystalline SrSi2

Motoharu Imai, Takashi Naka, Takao Furubayashi, Hideki Abe, Takao Nakama, and Katsuma Yagasaki

Appl. Phys. Lett. 86, 032102 (2005); http://dx.doi.org/10.1063/1.1849423 (3 pages) | Cited 15 times

Online Publication Date: 7 January 2005

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The electrical properties of polycrystalline SrSi2 were examined by electrical resistivity measurements at temperatures ranging from 2 to 760 K and Hall coefficient measurements at temperatures ranging from 10 to 300 K. These measurements revealed that SrSi2 is a narrow-gap semiconductor with an energy gap of 0.035 eV whose dominant carriers are holes.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Jc Other crystalline inorganic semiconductors

Influence of the gate leakage current on the stability of organic single-crystal field-effect transistors

R. W. I. de Boer, N. N. Iosad, A. F. Stassen, T. M. Klapwijk, and A. F. Morpurgo

Appl. Phys. Lett. 86, 032103 (2005); http://dx.doi.org/10.1063/1.1852089 (3 pages) | Cited 27 times

Online Publication Date: 7 January 2005

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We investigate the effect of a small leakage current through the gate insulator on the stability of organic single-crystal field-effect transistors (FETs). We find that, irrespective of the specific organic molecule and dielectric used, leakage current flowing through the gate insulator results in an irreversible degradation of the single-crystal FET performance. This degradation occurs even when the leakage current is several orders of magnitude smaller than the source-drain current. The experimental data indicate that a stable operation requires the leakage current to be smaller than 10−9 A/cm2. Our results also suggest that gate leakage currents may determine the lifetime of thin-film transistors used in applications.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Fr Low-field transport and mobility; piezoresistance

Bismuth ion-implanted solid-phase epitaxially grown shallow junction for metal–oxide–semiconductor field-effect transistors

Shahram Ghanad Tavakoli, Sungkweon Baek, Hyo Sik Chang, Dae Won Moon, and Hyunsang Hwang

Appl. Phys. Lett. 86, 032104 (2005); http://dx.doi.org/10.1063/1.1852731 (3 pages) | Cited 1 time

Online Publication Date: 7 January 2005

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A shallow, low-resistive solid phase epitaxially regrown n+/p junction was investigated for sub-70 nm metal–oxide–semiconductor field-effect transistors (MOSFETs), using bismuth (Bi) ion-implantation and low temperature rapid thermal annealing. Bi-doped specimens showed a shallow junction depth of ∼ 15 nm (at a background concentration of 5×1018 cm−3), low sheet resistance, and leakage current at low temperature processing (700 °C). The results indicated that Bi could be a proper dopant for low temperature activated source and drain extensions that are fabricated at low temperatures with the implementation of high-κ dielectric and metal–electrode gate stacks in next generation MOSFETs.
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78.40.Fy Semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases

Growth of ZnO/MgZnO quantum wells on sapphire substrates and observation of the two-dimensional confinement effect

B. P. Zhang, N. T. Binh, K. Wakatsuki, C. Y. Liu, Y. Segawa, and N. Usami

Appl. Phys. Lett. 86, 032105 (2005); http://dx.doi.org/10.1063/1.1850594 (3 pages) | Cited 60 times

Online Publication Date: 7 January 2005

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ZnO/MgZnO single quantum wells (QWs) in which the well width changes continuously were grown on sapphire (11math0) substrates by metalorganic chemical vapor deposition. Photoluminescence (PL) measurement revealed two emission peaks: one is position dependent and the other is not. Polarized PL spectra obtained from cleaved facets demonstrated perfect two-dimensional features of the position-dependent emission peak. The position-dependent peak was attributed to emissions due to excitons confined in the ZnO well layer, and the position-independent peak was attributed to emissions due to excitons in MgZnO barrier layers. The width dependence of the emission energy from the ZnO QW was interpreted by a simple theoretical model. Typical PL decay time of the QW emission was 360 ps at 77 K. It was shorter than that of the MgZnO barrier, 470 ps, due to the enhanced confinement effect in the QW.
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81.07.St Quantum wells
81.05.Dz II-VI semiconductors
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Et II-VI semiconductors

Electromagnetically induced transparency in alkali atoms integrated on a semiconductor chip

H. Schmidt and A. R. Hawkins

Appl. Phys. Lett. 86, 032106 (2005); http://dx.doi.org/10.1063/1.1853528 (3 pages) | Cited 5 times

Online Publication Date: 10 January 2005

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We analyze the integration of electromagnetically induced transparency in alkali atoms on a semiconductor chip. We propose the use of antiresonant reflecting optical waveguides with hollow cores to realize the necessary waveguiding capability and optical mode areas of a few square micrometers. We derive the scaling laws and limitations for the reduction in group velocity and single-photon phase shifts as a function of waveguide dimension. We show that miniaturization leads to a large enhancement of single-photon cross-phase modulation, despite the presence of additional limitations due to coherence dephasing and waveguide loss.
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42.82.Et Waveguides, couplers, and arrays
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.Gn Optical waveguides and couplers
51.70.+f Optical and dielectric properties

Intense terahertz laser fields on a two-dimensional electron gas with Rashba spin–orbit coupling

J. L. Cheng and M. W. Wu

Appl. Phys. Lett. 86, 032107 (2005); http://dx.doi.org/10.1063/1.1852732 (3 pages) | Cited 16 times

Online Publication Date: 11 January 2005

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The spin-dependent density of states and the density of spin polarization of an InAs-based two-dimensional electron gas with the Rashba spin–orbit coupling under an intense terahertz laser field are investigated by utilizing the Floquet states to solve the time-dependent Schrödinger equation. It is found that both densities are strongly affected by the terahertz laser field. Especially a terahertz magnetic moment perpendicular to the external terahertz laser field in the electron gas is induced. This effect can be used to convert terahertz electric signals into terahertz magnetic ones efficiently.
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73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
61.82.Fk Semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
72.25.Dc Spin polarized transport in semiconductors

Suppression of intrinsic bistability in resonant-tunneling diode by in-plane magnetic field

A. Yu. Serov and G. G. Zegrya

Appl. Phys. Lett. 86, 032108 (2005); http://dx.doi.org/10.1063/1.1853515 (3 pages) | Cited 3 times

Online Publication Date: 12 January 2005

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Using the Bardeen formalism, we calculated the electron tunneling through a double barrier structure with an in-plane magnetic field. It is shown that the in-plane magnetic field has two effects on the current–voltage characteristics. First, it reduces the width of the bistable region. At high magnetic fields, the bistability can be completely suppressed. This can provide a method for tuning the bistable region in a double barrier structure. Second, it modifies the peak current. The dependence of the peak current on the magnetic field is different in the cases of high and low electron concentrations in the quantum well.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
73.63.Hs Quantum wells
85.30.De Semiconductor-device characterization, design, and modeling

III-nitride metal-insulator-semiconductor heterojunction field-effect transistors using sputtered AlON thin films

Y. Cai, Y. G. Zhou, K. J. Chen, and K. M. Lau

Appl. Phys. Lett. 86, 032109 (2005); http://dx.doi.org/10.1063/1.1855403 (3 pages) | Cited 7 times

Online Publication Date: 12 January 2005

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In this letter, a III-nitride metal-insulator-semiconductor heterostructure field-effect transistors (MISHFET) was demonstrated by incorporating a sputtered AlON layer in the AlGaN/GaN heterostructure field-effect transistors (HFET). The AlON layer was deposited on the HFET structure by magnetron sputtering, followed by rapid thermal annealing at 850 °C for 45 s. A reverse gate leakage current that is four orders of magnitude lower was obtained in the MISHFET, compared to that in HFET. The MISHFET also shows 20% increase in the drain saturation current. For a MISHFET with 1‐μm-long gate, the current gain cutoff frequency, ft and the power gain cutoff frequency, fmax are measured to be 13 and 37 GHz, respectively.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing

Tunneling effects and intersubband absorption in AlN/GaN superlattices

E. Baumann, F. R. Giorgetta, D. Hofstetter, H. Wu, W. J. Schaff, L. F. Eastman, and L. Kirste

Appl. Phys. Lett. 86, 032110 (2005); http://dx.doi.org/10.1063/1.1849418 (3 pages) | Cited 14 times

Online Publication Date: 13 January 2005

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We report on intersubband absorption and photovoltage measurements on regular GaN/AlN-based superlattice structures. For barrier thicknesses larger than about 25 Å, the optical intersubband absorption peaks at a considerably smaller energy than the photovoltage spectrum. A simple model taking into account the oscillator strength of the involved transitions and the corresponding tunneling probabilities agrees with the experimental findings. According to this model, the observed photovoltage is the macroscopic manifestation that the two-dimensional electron gas at the top of the superlattice changes its carrier density by a vertical transport of electrons.
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73.21.Cd Superlattices
73.40.Gk Tunneling
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.50.Pz Photoconduction and photovoltaic effects
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.63.Hs Quantum wells
68.65.Cd Superlattices
68.65.Fg Quantum wells
73.21.Fg Quantum wells

Electrical properties of ZnO nanowire field effect transistors characterized with scanning probes

Zhiyong Fan and Jia G. Lu

Appl. Phys. Lett. 86, 032111 (2005); http://dx.doi.org/10.1063/1.1851621 (3 pages) | Cited 52 times

Online Publication Date: 13 January 2005

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Single ZnO nanowires are configured as field effect transistors and their electrical properties are characterized using scanning probe microscopy (SPM). Scanning surface potential microscopy is used to map the electric potential distribution on the nanowire. Potential drop along the nanowire and at the contacts are resolved, and contact resistances are estimated. Furthermore, conductive SPM tip is used as a local gate to manipulate the electrical property. The local change of electron density induced by a negatively biased tip significantly affects the current transport through the nanowire.
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85.30.Tv Field effect devices
85.35.−p
74.30.Cg
68.37.−d

Real-time monitoring and process control in amorphous∕crystalline silicon heterojunction solar cells by spectroscopic ellipsometry and infrared spectroscopy

Hiroyuki Fujiwara and Michio Kondo

Appl. Phys. Lett. 86, 032112 (2005); http://dx.doi.org/10.1063/1.1850612 (3 pages) | Cited 25 times

Online Publication Date: 13 January 2005

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In amorphous∕crystalline silicon heterojunction solar cells, we have performed real-time thickness control of hydrogenated amorphous silicon (a‐Si:H) layers with a precision better than ±1 Å by applying spectroscopic ellipsometry (SE). A heterojunction solar cell fabricated by this process shows a relatively high conversion efficiency of 14.5%. At the amorphous∕crystalline interface, however, infrared attenuated total reflection spectroscopy (ATR) revealed the formation of a porous a‐Si:H layer with a large SiH2-hydrogen content of 27 at. %. Based on SE and ATR results, we discuss the growth processes and structures of a‐Si:H in heterojunction solar cells.
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84.60.Jt Photoelectric conversion
78.30.Am Elemental semiconductors and insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Db Elemental semiconductors and insulators

Spin-polarized reflection in a two-dimensional electron system

Hong Chen, J. J. Heremans, J. A. Peters, A. O. Govorov, N. Goel, S. J. Chung, and M. B. Santos

Appl. Phys. Lett. 86, 032113 (2005); http://dx.doi.org/10.1063/1.1849413 (3 pages) | Cited 25 times

Online Publication Date: 14 January 2005

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We present a method to create spin-polarized beams of ballistic electrons in a two-dimensional electron system in the presence of spin–orbit interaction. Scattering of a spin-unpolarized injected beam from a lithographic barrier leads to the creation of two fully spin-polarized side beams, in addition to an unpolarized specularly reflected beam. Experimental magnetotransport data on InSb/InAlSb heterostructures demonstrate the spin-polarized reflection in a mesoscopic geometry.
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72.25.Dc Spin polarized transport in semiconductors
73.23.Ad Ballistic transport
72.25.Mk Spin transport through interfaces
72.25.Rb Spin relaxation and scattering
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.40.Cg Contact resistance, contact potential
73.50.Fq High-field and nonlinear effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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Josephson junctions with nonlinear damping for rapid single-flux-quantum - qubit circuits

A. B. Zorin, M. I. Khabipov, D. V. Balashov, R. Dolata, F.-I. Buchholz, and J. Niemeyer

Appl. Phys. Lett. 86, 032501 (2005); http://dx.doi.org/10.1063/1.1852076 (3 pages) | Cited 10 times

Online Publication Date: 7 January 2005

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We demonstrate that shunting of superconductor-insulator-superconductor (S-I-S) Josephson junctions by superconductor-insulator-normal metal (S-I-N) structures having pronounced nonlinear I–V characteristics can remarkably modify the Josephson dynamics. In the regime of Josephson generation the phase behaves as an overdamped coordinate, while in the superconducting state the damping and current noise are strikingly small, that is vitally important for application of such junctions for readout and control of Josephson qubits. Superconducting Nb/AlOx/Nb junction shunted by Nb/AlOx/AuPd junction of S-I-N type was fabricated and, in agreement with our model, exhibited nonhysteretic I–V characteristics at temperatures down to at least 1.4 K.
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85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
85.25.Cp Josephson devices

High sensitivity of positive magnetoresistance in low magnetic field in perovskite oxide p–n junctions

H. B. Lu, S. Y. Dai, Z. H. Chen, Y. L. Zhou, B. L. Cheng, K. J. Jin, L. F. Liu, G. Z. Yang, and X. L. Ma

Appl. Phys. Lett. 86, 032502 (2005); http://dx.doi.org/10.1063/1.1850192 (3 pages) | Cited 57 times

Online Publication Date: 7 January 2005

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Large positive magnetoresistance (MR) and high MR sensitivity in low magnetic fields have been discovered in the Sr-doped LaMnO3 and Nb-doped SrTiO3 p–n junctions fabricated by laser molecular-beam epitaxy. The MR ratios, defined as ΔR/R0, ΔR = RH−R0, are observed as large as 11% in 5 Oe, 23% in 100 Oe, and 26% in 1000 Oe at 290 K; 53% in 5 Oe, 80% in 100 Oe, and 94% in 1000 Oe at 255 K. The MR sensitivities are 85 Ω/Oe at 290 K, 246 Ω/Oe at 255 K, and 136 Ω/Oe at 190 K, respectively, with the applied magnetic field changed from 0 to 5 Oe. The positive MR ratios and high MR sensitivities of the p–n junctions are very different from that of the LaMnO3 compound family.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.50.Dd Nonmetallic ferromagnetic materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
73.43.Qt Magnetoresistance
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ng Insulators
75.47.Lx Magnetic oxides
68.55.-a Thin film structure and morphology
42.62.-b Laser applications

In situ detection method for obtaining permeability of Fe-based amorphous alloys: ac resistance measurement for Fe84Nb7B9

Tetsu Ichitsubo, Eiichiro Matsubara, Satoshi Tanaka, Nobuyuki Nishiyama, and Kenji Amiya

Appl. Phys. Lett. 86, 032503 (2005); http://dx.doi.org/10.1063/1.1852713 (3 pages) | Cited 1 time

Online Publication Date: 7 January 2005

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In this letter, we propose an in situ detection method for obtaining permeability of soft magnetic Fe-based amorphous alloys. The temperature dependence of ac resistance was measured at different frequencies during heat treatment of Fe84Nb7B9 amorphous alloys. A significant increase in the ac ( ∼ 1000 kHz) resistance appears at around 920 K during the heating process, which arises from the skin effect caused by a marked increase in sample permeability. This skin effect diminishes when the sample is heated to approximately 1100 K, which corresponds to the decrease in its permeability. Consequently, we note that the ac resistance measurement is useful for quick in situ assessment to achieve the soft magnetic property of an Fe-based amorphous alloy.
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75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.05.Bx Metals, semimetals, and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
81.40.Gh Other heat and thermomechanical treatments
72.30.+q High-frequency effects; plasma effects

Domain wall coupling and collective switching in interacting mesoscopic ring magnet arrays

M. Kläui, C. A. F. Vaz, J. A. C. Bland, and L. J. Heyderman

Appl. Phys. Lett. 86, 032504 (2005); http://dx.doi.org/10.1063/1.1846954 (3 pages) | Cited 20 times

Online Publication Date: 7 January 2005

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The effects of magnetostatic domain wall coupling on the magnetic switching are investigated for micrometer-sized cobalt ring arrays with edge-to-edge spacings varying between 80 nm and 8 μm. The various transitions between the different equilibrium states in rings are affected differently with increasing magnetostatic interaction (leading to an increased or reduced switching field) depending on the details of the particular switching mechanism. The switching field distribution width is strongly reduced for narrowly spaced ring arrays due to collective switching between adjacent rings where the domain walls couple magnetostatically. The interaction is found to increase with increasing film thickness due to the increased stray field.
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75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.30.Et Exchange and superexchange interactions
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.-a Thin film structure and morphology

Rare earth ion size effects and enhanced critical current densities in Y2/3Sm1/3Ba2Cu3O7−x coated conductors

J. L. MacManus-Driscoll, S. R. Foltyn, B. Maiorov, Q. X. Jia, H. Wang, A. Serquis, L. Civale, Y. Lin, M. E. Hawley, M. P. Maley, and D. E. Peterson

Appl. Phys. Lett. 86, 032505 (2005); http://dx.doi.org/10.1063/1.1851006 (3 pages) | Cited 26 times

Online Publication Date: 10 January 2005

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The influence of rare earth (RE) ion size on critical current density (Jc) in epitaxial films of superconducting REBa2Cu3O7−x was studied, where RE is the mixture of two or three rare earth ions. No systematic dependence of Jc on RE ion size was found. However, strongly enhanced critical current densities (Jc’s) were found for the composition Y2/3Sm1/3Ba2Cu3O7−x (YSmBCO). In ∼ 1‐μm-thick films, Jc’s as high as 4.7×106 A cm−2 (75.5 K, 0 T) and 11×104 A cm−2 (75.5 K, 5 T) were obtained on single crystals and 6×104 A cm−2 (75.5 K, 5 T) on buffered metal. The values are up to a factor of 3 higher than for comparative YBCO samples.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents

Ferromagnetic Mn-doped GaN nanowires

Doo Suk Han, Jeunghee Park, Kung Won Rhie, Soonkyu Kim, and Joonyeon Chang

Appl. Phys. Lett. 86, 032506 (2005); http://dx.doi.org/10.1063/1.1852725 (3 pages) | Cited 43 times

Online Publication Date: 10 January 2005

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We report Mn-doped GaN nanowires exhibiting ferromagnetism even at room temperature. The growth of single-crystalline wurtzite-structured GaN nanowires doped homogeneously with about 5 at. % Mn was achieved by chemical vapor deposition using the reaction of Ga∕GaN∕MnCl2 with NH3. The ferromagnetic hysteresis at 5 and 300 K and the temperature-dependent magnetization curves suggest the Curie temperature around 300 K. Negative magnetoresistance of individual nanowires was observed at the temperatures below 150 K.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Pq Other materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.20.Uv Electron energy loss spectroscopy

Electron paramagnetic resonance studies of the high-spin molecule Cr10(OMe)20(O2CCMe3)10

Sonia Sharmin, Arzhang Ardavan, Stephen J. Blundell, Amalia I. Coldea, Eric J. L. McInnes, and David Low

Appl. Phys. Lett. 86, 032507 (2005); http://dx.doi.org/10.1063/1.1851613 (3 pages) | Cited 3 times

Online Publication Date: 12 January 2005

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We report millimeter-wave magneto-optical measurements on the high-spin molecule, Cr10(OMe)20(O2CCMe3)10. The dependence of the electron paramagnetic resonance as a function of orientation and temperature demonstrates that this compound behaves as a single molecule magnet, and exhibits one of the smallest zero-field splittings (D = −0.045±0.004 K) yet reported for such a system.
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75.50.Xx Molecular magnets
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.70.Gq Microwave and radio-frequency interactions
78.20.Ls Magneto-optical effects
75.10.Dg Crystal-field theory and spin Hamiltonians

Magnetoelectric resonance-bandwidth broadening of Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers in parallel and series connections

H. Yu, M. Zeng, Y. Wang, J. G. Wan, and J.-M. Liu

Appl. Phys. Lett. 86, 032508 (2005); http://dx.doi.org/10.1063/1.1854736 (3 pages) | Cited 15 times

Online Publication Date: 12 January 2005

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The bandwidth of magnetoelectric (ME) resonance for a combined structure where several Terfenol-D/epoxy-Pb(Zr,Ti)O3 bilayers are connected in parallel and series was measured. A relationship between the bilayer length and resonance frequency was used to design the combined structure, in which the bilayered components of different lengths were connected in the parallel and series forms, respectively. The measured giant ME effect of the combined structure showed a much wider frequency response to external field than a single bilayered structure, and the ME effect far from the resonance ranges was enhanced significantly too. A qualitative analysis based on the equivalent circuit concept was presented to explain these effects.
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75.80.+q Magnetomechanical effects, magnetostriction
77.55.-g Dielectric thin films
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
77.65.Fs Electromechanical resonance; quartz resonators
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
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