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19 Apr 2004

Volume 84, Issue 16, pp. 2971-3207

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3139 (2004); http://dx.doi.org/10.1063/1.1710717 (3 pages)

Slava V. Rotkin and Karl Hess
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Time-resolved photoluminescence of InAs quantum dots in a GaAs quantum well

F. Pulizzi, A. J. Kent, A. Patanè, L. Eaves, and M. Henini

Appl. Phys. Lett. 84, 3046 (2004); http://dx.doi.org/10.1063/1.1713052 (3 pages) | Cited 10 times

Online Publication Date: 13 April 2004

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We study the time-resolved photoluminescence emission of InAs self-assembled quantum dots (QDs) incorporated in a GaAs/(AlGa)As quantum well. We show that the quantum well confinement affects the decay time of the dot photoluminescence. In addition, we use the strong dependence of the decay time on excitation energy and temperature to shed light on carrier relaxation mechanisms in QDs. © 2004 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.47.-p Spectroscopy of solid state dynamics

Determination of the ionization energy of nitrogen acceptors in zinc oxide using photoluminescence spectroscopy

Lijun Wang and N. C. Giles

Appl. Phys. Lett. 84, 3049 (2004); http://dx.doi.org/10.1063/1.1711162 (3 pages) | Cited 34 times

Online Publication Date: 13 April 2004

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Photoluminescence spectroscopy of nitrogen-related emissions in ZnO is used to establish the ionization energy of the substitutional nitrogen acceptor. The temperature dependence of the nitrogen-related electron-acceptor (e,A0) emission band has been monitored in as-grown single crystals of ZnO. Line shape analysis of this band is used to determine the acceptor ionization energy. The temperature dependence of the band gap for ZnO was included in our analysis and the low-temperature acceptor ionization energy for substitutional nitrogen at an oxygen site in ZnO was found to be EA = 209±3 meV. Our line shape analysis indicates a small temperature-dependent decrease in EA for T>5 K. © 2004 American Institute of Physics.
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81.05.Dz II-VI semiconductors
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
81.10.Bk Growth from vapor
71.20.Nr Semiconductor compounds

Femtosecond studies of electron capture times in InGaN/GaN multiple quantum wells

W. H. Fan, S. M. Olaizola, J.-P. R. Wells, A. M. Fox, T. Wang, P. J. Parbrook, D. J. Mowbray, and M. S. Skolnick

Appl. Phys. Lett. 84, 3052 (2004); http://dx.doi.org/10.1063/1.1707226 (3 pages) | Cited 3 times

Online Publication Date: 13 April 2004

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Subpicosecond time-resolved differential transmission spectroscopy has been used to investigate the carrier density and temperature dependence of the quantum well electron capture time of blue-emitting InGaN/GaN multiple quantum well structures. It is found that the capture time varies significantly with both temperature and carrier density, the latter effect being consistent with carrier-induced band bending or increased carrier–carrier scattering. At room temperature, the electron capture time is in the range 0.4–0.8 ps for carrier densities ⩽ 5×1018 cm−3. © 2004 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.De Quantum wells
73.21.Fg Quantum wells
73.21.Cd Superlattices

Fracture toughness from submicron derived indentation cracks

T. Scholz, G. A. Schneider, J. Muñoz-Saldaña, and M. V. Swain

Appl. Phys. Lett. 84, 3055 (2004); http://dx.doi.org/10.1063/1.1711164 (3 pages) | Cited 28 times

Online Publication Date: 13 April 2004

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Indentation tests with loads between 0.5 and 10 mN were performed on fused quartz, (0001) oriented sapphire and (001) oriented barium titanate. The resulting submicron cracks were used to determine the fracture toughness KIC of the tested samples. The indentation crack length method was applicable, but a c/a dependency of the constant of proportionality was found. In addition, a very effective and simple approach—using the extra penetration of the indenter, due to the formation of cracks, so called pop-in—was used to determine KIC. © 2004 American Institute of Physics.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
68.35.Gy Mechanical properties; surface strains
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
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Scattering mechanisms in high-mobility strained Ge channels

B. Rössner, D. Chrastina, G. Isella, and H. von Känel

Appl. Phys. Lett. 84, 3058 (2004); http://dx.doi.org/10.1063/1.1707223 (3 pages) | Cited 34 times

Online Publication Date: 13 April 2004

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We report on the low-temperature mobility in remotely doped p-type strained Ge layers on relaxed Si0.3Ge0.7 virtual substrates, grown by low-energy plasma-enhanced chemical vapor deposition. A maximum mobility of 120 000 cm2 V−1 s−1 has been reached at 2 K, at a carrier sheet density of 8.5×1011 cm−2. Analysis of the mobility and Dingle ratio τ/τq as a function of sheet density suggests that remote impurity scattering is the limiting factor at low sheet densities, but that interface impurities become more important as the sheet density increases. © 2004 American Institute of Physics.
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81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
61.72.uf Ge and Si
72.20.Dp General theory, scattering mechanisms
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effect of impurities on the mobility of single crystal pentacene

Oana D. Jurchescu, Jacob Baas, and Thomas T. M. Palstra

Appl. Phys. Lett. 84, 3061 (2004); http://dx.doi.org/10.1063/1.1704874 (3 pages) | Cited 311 times

Online Publication Date: 13 April 2004

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We have obtained a hole mobility for the organic conductor pentacene of μ=35 cm2/V s at room temperature increasing to μ = 58 cm2/V s at 225 K. These high mobilities result from a purification process in which 6,13-pentacenequinone was removed by vacuum sublimation. The number of traps is reduced by two orders of magnitude compared with conventional methods. The temperature dependence of the mobility is consistent with the band model for electronic transport. © 2004 American Institute of Physics.
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81.20.Ym Purification
61.72.S- Impurities in crystals
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)

Comparison of the electrical activation of P+ and N+ ions co-implanted along with Si+ or C+ ions into 4H-SiC

F. Schmid and G. Pensl

Appl. Phys. Lett. 84, 3064 (2004); http://dx.doi.org/10.1063/1.1707220 (3 pages) | Cited 6 times

Online Publication Date: 13 April 2004

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The annealing behavior of P+ and N+ ions implanted into p-type 4H-SiC epilayers is studied by a temperature-dependent Hall-effect. Detailed investigations reveal that the electrical activation of implanted P+ ions is governed by the site competition effect, while implanted N+ ions react with intrinsic defects during the annealing step and can form thermally stable and electrically inactive complexes. In this way, the electrical activation of implanted N+ ions is strongly reduced. © 2004 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
71.55.Eq III-V semiconductors

Photoemission study and band alignment of the CuInSe2(001)/CdS heterojunction

T. Schulmeyer, R. Hunger, A. Klein, W. Jaegermann, and S. Niki

Appl. Phys. Lett. 84, 3067 (2004); http://dx.doi.org/10.1063/1.1712034 (3 pages) | Cited 12 times

Online Publication Date: 13 April 2004

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The contact formation of thin-film epitaxial CuInSe2(001) with a physical-vapor-deposited CdS layer is presented in this work. Synchrotron-excited photoelectron spectroscopy was used for this investigation. The epitaxial CuInSe2 films contain a surface layer of reduced Cu stoichiometry similar to the ordered defect compound CuIn3Se5. A valence band offset of 0.79±0.15 eV has been determined for this heterojunction. The comparison to literature data indicates that neither surface orientation nor surface copper content have a major impact on the valence band offset of CuIn3Se5, respectively, CuInSe2 with CdS. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
79.60.Dp Adsorbed layers and thin films
61.66.Bi Elemental solids
61.66.Dk Alloys
73.20.At Surface states, band structure, electron density of states

Surface band bending in as-grown and plasma-treated n-type GaN films using surface potential electric force microscopy

Sang-Jun Cho, Seydi Doğan, Shahriar Sabuktagin, Michael A. Reshchikov, Daniel K. Johnstone, and Hadis Morkoç

Appl. Phys. Lett. 84, 3070 (2004); http://dx.doi.org/10.1063/1.1703843 (3 pages) | Cited 24 times

Online Publication Date: 13 April 2004

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The surface band bending, as well as the effect of plasma-induced damage on band bending, on GaN surfaces, was investigated. The upward band bending, measured by surface potential electric force microscopy (a variant of atomic force microscopy), for the as-grown n-type GaN was about 1.0 eV which increased to ∼ 1.4 eV after reactive ion etching (RIE). UV illumination decreased the band bending by 0.3 eV with time constants on the order of seconds and hundreds of seconds for the as-grown and RIE treated GaN, respectively. This implies that there is a higher density of the surface states in the samples subjected to the RIE process. After the RIE treatment, the shape of the photoluminescence spectrum remained unchanged, but the intensity dropped by a factor of 3. This effect can be attributed to nonradiative defects created near the surface by the RIE treatment. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.At Surface states, band structure, electron density of states
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Electrical isolation, thermal stability and rf loss in a multilayer GaAs planar doped barrier diode structure bombarded by H+ and Fe+ ions

V. T. Vo, K. L. Koon, Z. R. Hu, C. N. Dharmasiri, S. C. Subramaniam, and A. A. Rezazadeh

Appl. Phys. Lett. 84, 3073 (2004); http://dx.doi.org/10.1063/1.1712030 (3 pages) | Cited 1 time

Online Publication Date: 13 April 2004

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Electrical isolation in multilayer GaAs planar doped barrier (PDB) diode structures produced by H+ and Fe+ ion implantation were investigated. For an H+ bombardment with a dose of 1×1015 cm−2, a sheet resistivity as high as 3×108 Ω/sq and thermal stability up to 400 °C has been achieved. For samples bombarded by Fe+ ions, a similar high sheet resistivity has also been achieved although a longer annealing time (15 min) and a higher annealing temperature (550 °C) were needed. The rf dissipation losses of coplanar waveguide (CPW) “thru” lines fabricated on bombarded multilayer PDBD structure samples were also examined. The measured rf losses were 1.65 dB/cm at 10 GHz and 3 dB/cm at 40 GHz, similar to the values that a CPW line exhibits on a semi-isolating GaAs substrate. © 2004 American Institute of Physics.
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68.65.Ac Multilayers
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
85.30.Kk Junction diodes
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Transport mechanisms in atomic-layer-deposited Al2O3 dielectrics

M. Specht, M. Städele, S. Jakschik, and U. Schröder

Appl. Phys. Lett. 84, 3076 (2004); http://dx.doi.org/10.1063/1.1703840 (3 pages) | Cited 36 times

Online Publication Date: 13 April 2004

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We analyze the field and temperature dependence of electron currents through atomic-layer-deposited thin (3.6–6 nm) sheets of Al2O3 which were annealed above the crystallization temperature. On the basis of electrical characterization and numerical simulation that includes trap-assisted transport as well as the band bending in the contact regions, we have identified three characteristic field regions in which the currents are dominated by elastic trap-assisted tunneling, Frenkel–Poole hopping, or Fowler–Nordheim tunneling. We find that the Frenkel–Poole traps lie in a narrow band about 1.2 eV below the conduction band minimum of Al2O3, whereas the energetic distribution of the elastic traps is broad and has a tail that reaches far into the band gap. The numerical results are compatible with a Si/Al2O3 conduction band offset of 2.7 eV. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
73.50.Fq High-field and nonlinear effects
71.20.Ps Other inorganic compounds
73.40.Gk Tunneling
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments

Direct and highly sensitive measurement of defect-related absorption in amorphous silicon thin films by cavity ringdown spectroscopy

I. M. P. Aarts, B. Hoex, A. H. M. Smets, R. Engeln, W. M. M. Kessels, and M. C. M. van de Sanden

Appl. Phys. Lett. 84, 3079 (2004); http://dx.doi.org/10.1063/1.1713047 (3 pages) | Cited 21 times

Online Publication Date: 13 April 2004

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Cavity ringdown spectroscopy has been applied to hydrogenated amorphous silicon (a-Si:H) showing that this fully optical method is suited for the detection of defect-related absorption in thin films with a minimal detectable absorption of 1×10−6 per laser pulse and without the need for a calibration procedure. Absolute absorption coefficient spectra for photon energies between 0.7 and 1.7 eV have been obtained for thin a-Si:H films (4–98 nm) revealing a different spectral dependence for defects located in the bulk and in the surface/interface region of a-Si:H. © 2004 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Heteroepitaxial growth of (111) 3C–SiC on well-lattice-matched (110) Si substrates by chemical vapor deposition

Taro Nishiguchi, Mitsuhiro Nakamura, Koji Nishio, Toshiyuki Isshiki, and Shigehiro Nishino

Appl. Phys. Lett. 84, 3082 (2004); http://dx.doi.org/10.1063/1.1719270 (3 pages) | Cited 17 times

Online Publication Date: 13 April 2004

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Heteroepitaxial growth of 3C–SiC on (110) Si substrates by chemical vapor deposition was carried out, and the grown epitaxial layers were investigated by high resolution transmission electron microscopic (HRTEM) analysis. The interface structure between 3C–SiC and Si substrates depended on the flow rate of C3H8 during the carbonization process. In the case of the growth under C3H8 = 0.4 sccm, the interface was flat and 3C–SiC layer was grown epitaxially on (110) Si substrate in a well-lattice-matched relationship of (110) Si//(111) 3C–SiC and [math10] Si//[math10] 3C–SiC. In contrast, the interface was rough under C3H8 = 1.2 sccm and polycrystalline 3C–SiC grew without epitaxial relationship to the substrate. HRTEM observations revealed that an atomically flat (110) Si substrate surface is significant in order to grow high quality 3C–SiC with suppressing the generation of stacking faults. © 2004 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects

Positive temperature coefficient resistance and humidity sensing properties of Cd-doped ZnO nanowires

Q. Wan, Q. H. Li, Y. J. Chen, T. H. Wang, X. L. He, X. G. Gao, and J. P. Li

Appl. Phys. Lett. 84, 3085 (2004); http://dx.doi.org/10.1063/1.1707225 (3 pages) | Cited 63 times

Online Publication Date: 13 April 2004

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Cd-doped ZnO nanowires in mass production were synthesized by evaporating metal zinc (Zn) and cadmium (Cd) at 900 °C. Devices using the synthesized nanowires were fabricated on microstructured substrates. Cd-doped ZnO nanowires show a clear positive temperature coefficient of resistance effect, which is quite abnormal as compared to pure ZnO nanowires. At room temperature, resistance change of more than three orders of magnitude was measured when Cd-doped ZnO nanowire device was exposed to a moisture pulse of 95% relative humidity. © 2004 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.07.Vx Hygrometers; hygrometry
73.63.Nm Quantum wires
61.46.-w Structure of nanoscale materials
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.07.Bc Nanocrystalline materials
61.72.uj III-V and II-VI semiconductors
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Anomalous threshold voltage change by 2 MeV electron irradiation at 100 °C in deep submicron metal-oxide-semiconductor field-effect transistors

K. Hayama, H. Ohyama, E. Simoen, J. M. Rafí, A. Mercha, and C. Claeys

Appl. Phys. Lett. 84, 3088 (2004); http://dx.doi.org/10.1063/1.1711170 (3 pages) | Cited 1 time

Online Publication Date: 13 April 2004

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The degradation of the electrical properties of deep submicron metal-oxide-semiconductor field-effect transistors (MOSFETs) by 2 MeV electron irradiation at high temperatures was studied. The irradiation temperatures were 30, 100, 150 and 200 °C, and the fluence was fixed at 1015 e/cm2. For most experimental conditions, the threshold voltage (VT) is observed to reduce in absolute value both for n- and p-MOSFETs. This reduction is most pronounced at 100 °C, as at this irradiation temperature, the radiation-induced density of interface traps is highest. It is proposed that hydrogen neutralization of the dopants in the substrate plays a key role, whereby the hydrogen is released from the gate by the 2 MeV electrons. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
61.80.Fe Electron and positron radiation effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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Exploration of artificial multiferroic thin-film heterostructures using composition spreads

K.-S. Chang, M. A. Aronova, C.-L. Lin, M. Murakami, M.-H. Yu, J. Hattrick-Simpers, O. O. Famodu, S. Y. Lee, R. Ramesh, M. Wuttig, I. Takeuchi, C. Gao, and L. A. Bendersky

Appl. Phys. Lett. 84, 3091 (2004); http://dx.doi.org/10.1063/1.1699474 (3 pages) | Cited 41 times

Online Publication Date: 13 April 2004

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We have fabricated a series of composition spreads consisting of ferroelectric BaTiO3 and piezomagnetic CoFe2O4 layers of varying thicknesses modulated at nanometer level in order to explore artificial magnetoelectric thin-film heterostructures. Scanning microwave microscopy and scanning superconducting quantum interference device microscopy were used to map the dielectric and magnetic properties as a function of continuously changing average composition across the spreads, respectively. Compositions in the middle of the spreads were found to exhibit ferromagnetism while displaying a dielectric constant as high as ≈ 120. © 2004 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Tt Fine-particle systems; nanocrystalline materials
77.55.-g Dielectric thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Crystal structure and magnetic properties of SmCo5.85Si0.90 compound

J. Luo, J. K. Liang, Y. Q. Guo, Q. L. Liu, L. T. Yang, F. S. Liu, and G. H. Rao

Appl. Phys. Lett. 84, 3094 (2004); http://dx.doi.org/10.1063/1.1712026 (3 pages) | Cited 32 times

Online Publication Date: 13 April 2004

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The crystal structure and magnetic properties of SmCo7−xSix (x = 0.1–0.9) compounds were studied by means of x-ray powder diffraction and magnetic measurements. Rietveld refinement of x-ray powder diffraction pattern shows that the as-cast compound SmCo7−xSix with x = 0.9 crystallizes in the TbCu7-type structure with the space group P6/mmm, and the doping element Si has a distinct preference to occupy the 3g site. According to the refinement result, the composition of the compound is derived as SmCo5.85Si0.90. The compound SmCo5.85Si0.90 exhibits ferromagnetic order with the Curie temperature of about 717 K and a saturation moment of about 6.58±0.05 μB/f.u. The SmCo5.85Si0.90 compound shows a strong uniaxial magnetocrystalline anisotropy, and an anomalous increase of magnetization at low temperature is observed in an external field applied perpendicular to the easy direction of magnetization. © 2004 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
64.70.K- Solid-solid transitions

Giant magnetoresistance in PtMn alloys

M. J. Carey, A. B. Banful, L. Folks, B. A. Gurney, R. F. C. Farrow, and A. J. Kellock

Appl. Phys. Lett. 84, 3097 (2004); http://dx.doi.org/10.1063/1.1712022 (3 pages) | Cited 6 times

Online Publication Date: 13 April 2004

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The onset of chemical and magnetic order in PtMn is accompanied by a large increase in the resistivity, ρ, contrary to that observed in nonmagnetic or ferromagnetic disorder–order transitions. We attribute this to a giant magnetoresistance like magnetic scattering off the antiferromagnetically aligned spins within the PtMn. The characteristics of the resistance change with anneal time in two regimes, with only the second regime involving a disorder/order transition. We have used the change of ρ with time to calculate the activation energy for the L10 transformation in PtMn and found it to be about 1.5 eV for thick films. The activation energy increases significantly for thinner films. © 2004 American Institute of Physics.
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75.50.Ee Antiferromagnetics
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
75.47.De Giant magnetoresistance
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Transition of magnetic state from A-type antiferromagnetic to ferromagnetic in electron-doped Nd1−xCexMnO3

Shixiong Zhang, Lan Luan, Shun Tan, and Yuheng Zhang

Appl. Phys. Lett. 84, 3100 (2004); http://dx.doi.org/10.1063/1.1712023 (3 pages) | Cited 6 times

Online Publication Date: 13 April 2004

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The transition of the magnetic state with x increasing in electron-doped manganite Nd1−xCexMnO3 is investigated through the measurements of magnetism, including the M–T and hysteresis curves. For x = 0.04, with temperature increasing, M under zero-field cooling indicates that the magnetic structure changes from ferromagnetic (FM) to antiferromagnetic then to FM again and finally turns to paramagnetic (PM). However, the field-cooling M–T curve shows a negative M at 5 K then increases rapidly to a positive maximum and finally turns to PM. The experiment results are well fitted with Weiss’s molecular field theory and Néel’s ferrimagnetic model. With the enhancement of Ce content (x = 0.08 and 0.10), this system gradually exhibits simple transition from FM to PM. © 2004 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Spin momentum transfer in current perpendicular to the plane spin valves

M. Covington, A. Rebei, G. J. Parker, and M. A. Seigler

Appl. Phys. Lett. 84, 3103 (2004); http://dx.doi.org/10.1063/1.1707227 (3 pages) | Cited 3 times

Online Publication Date: 13 April 2004

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We present experimental and numerical micromagnetic data on the effect of spin momentum transfer in current perpendicular to the plane spin valves. Starting from a configuration with orthogonal free- and pinned-layer magnetizations, the free-layer magnetization exhibits abrupt current-induced switching that is qualitatively consistent with the spin torque model. When operating the spin valve as a field sensor, spin transfer can produce a change in resistance that mimics an effective magnetic field and induce magnetic instability that requires a larger bias field in order to stabilize the device. © 2004 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics

Spin-dependent single-electron-tunneling effects in epitaxial Fe nanoparticles

F. Ernult, K. Yamane, S. Mitani, K. Yakushiji, K. Takanashi, Y. K. Takahashi, and K. Hono

Appl. Phys. Lett. 84, 3106 (2004); http://dx.doi.org/10.1063/1.1712035 (3 pages) | Cited 25 times

Online Publication Date: 13 April 2004

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Fe/MgO/Fe nanoparticles/MgO/Co double tunnel junctions were prepared by molecular beam epitaxy for current-perpendicular-to-plane transport measurements on submicrometer-sized pillars. Microstructural observations indicate that the samples exhibit a fully epitaxial layered structure with sharp and flat interfaces including well-defined separated Fe nanoparticles between the barriers. The introduction of asymmetric MgO tunnel barriers, i.e., with different thicknesses, in the double junction leads to a clear observation of Coulomb staircase and associated tunnel magnetoresistance oscillations. An estimation of the capacitance of the system indicates that these transport phenomena are due to charging effects of the magnetic particles. © 2004 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.23.Hk Coulomb blockade; single-electron tunneling

Effect of sample size on magnetic Jc for MgB2 superconductor

J. Horvat, S. Soltanian, X. L. Wang, and S. X. Dou

Appl. Phys. Lett. 84, 3109 (2004); http://dx.doi.org/10.1063/1.1713031 (3 pages) | Cited 18 times

Online Publication Date: 13 April 2004

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A strong effect of sample size on magnetic Jc(H) was observed for bulk MgB2 when Jc is obtained directly from the critical state model. Thus obtained zero-field Jc (Jc0) decreases strongly with the sample size, attaining a constant value for the samples larger than a few millimeters. On the other hand, the irreversibility field (Hirr) defined at Jc = 100 A/cm2 increases with the sample size. The decrease of Jc0 is described in terms of voids in the bulk MgB2 samples and superconducting screening around the cells of superconducting material between these voids (35 μm), because of concentration of the current in the narrow bridges connecting the cells. For samples larger than a few millimeters, the value of magnetic Jc is in agreement with the transport Jc and it is restricted by the voids. The critical state model is not suitable for obtaining Jc for small bulk MgB2. The increase of Hirr with the sample size is an artifact of defining Hirr by the value of Jc at which an additional superconducting screening on 1 μm scale dominates Δm. © 2004 American Institute of Physics.
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74.25.Sv Critical currents
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Optical and magneto-optical studies of two-dimensional metallodielectric photonic crystals on cobalt films

M. Diwekar, V. Kamaev, J. Shi, and Z. V. Vardeny

Appl. Phys. Lett. 84, 3112 (2004); http://dx.doi.org/10.1063/1.1712027 (3 pages) | Cited 28 times

Online Publication Date: 13 April 2004

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We studied the optical transmission and magneto-optical effect through a subwavelength hole array fabricated on a ferromagnetic cobalt (Co) thin film in comparison to a control unperforated Co film having the same thickness. We found that the perforated film sustains extraordinary transmission bands through the hole array, which can be well explained as due to light coupling to surface plasmons on the two film interfaces. We also found that due to resonant coupling to the surface plasmons, the magneto-optical Kerr effect in the spectral range of the anomalous transmission bands of the perforated Co film is much smaller than that in the control Co film. © 2004 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
75.50.Cc Other ferromagnetic metals and alloys
42.70.Qs Photonic bandgap materials
78.20.Ls Magneto-optical effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Faraday rotation in Co0.85Zn0.15Fe2O4 spinel ferrite nanoparticulate films under low applied fields

Richard M. Anderson, Christy R. Vestal, Anna C. S. Samia, and Z. John Zhang

Appl. Phys. Lett. 84, 3115 (2004); http://dx.doi.org/10.1063/1.1712031 (3 pages) | Cited 7 times

Online Publication Date: 13 April 2004

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Films of Co0.85Zn0.15Fe2O4 nanoparticles were prepared on silanized glass substrates using aminobenzoic acid/imidazole-modified magnetic nanoparticles. Dispersive Faraday rotations in the nanoparticulate films were observed as 1.0°–3.0° under relatively low applied magnetic field strengths of less than 500 Oe. The magnitude of the Faraday rotation increases with increasing thickness of the prepared films. No differences in the Faraday rotation were observed for Co0.85Zn0.15Fe2O4 nanoparticles as the particle size varied from 12 to 18 nm. © 2004 American Institute of Physics.
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75.50.Gg Ferrimagnetics
61.46.-w Structure of nanoscale materials
81.07.Wx Nanopowders
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects

Observation of spin-transfer switching in deep submicron-sized and low-resistance magnetic tunnel junctions

Yiming Huai, Frank Albert, Paul Nguyen, Mahendra Pakala, and Thierry Valet

Appl. Phys. Lett. 84, 3118 (2004); http://dx.doi.org/10.1063/1.1707228 (3 pages) | Cited 172 times

Online Publication Date: 13 April 2004

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The spin-transfer effect has been studied in magnetic tunnel junctions (PtMn/CoFe/Ru/CoFe/Al2O3/CoFe/NiFe) with dimensions down to 0.1×0.2 μm2 and resistance–area product RA in the range of 0.5–10 Ω μm2 (ΔR/R = 1%–20%). Current-induced magnetization switching is observed with a critical current density of about 8×106 A/cm2. The attribution of the switching to the spin-transfer effect is supported by a current-induced ΔR/R value identical to the one obtained from the R versus H measurements. Furthermore, the critical switching current density has clear dependence on the applied magnetic field, consistent with what has been observed previously in the case of spin-transfer-induced switching in metallic multilayer systems. © 2004 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
72.25.Mk Spin transport through interfaces
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
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