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12 May 2003

Volume 82, Issue 19, pp. 3147-3362

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Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages)

Michael Mück, Christian Welzel, and John Clarke
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Superconducting quantum interference device amplifiers at gigahertz frequencies

Michael Mück, Christian Welzel, and John Clarke

Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages) | Cited 22 times

Online Publication Date: 6 May 2003

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A series of five dc superconducting quantum interference devices (SQUIDs) have been operated as microstrip amplifiers at frequencies ranging from 2.2 to 7.4 GHz. In these devices, the signal is connected between the SQUID washer and coil, which acts as a microstrip resonator. The gain measured at 4.2 K ranged from 12±1 to 6±1 dB. The noise temperature of three devices at 4.2 K in the frequency range 2.2–4 GHz was between 1 and 2 K, and the saturation temperature was between 150 and 250 K. Applications of these devices include readout for axion detectors, and intermediate-frequency amplifiers for superconductor–insulator–superconductor and hot-electron bolometer mixers. © 2003 American Institute of Physics.
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84.30.Le Amplifiers
84.40.Dc Microwave circuits
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Growth and characterization of TiO2 as a barrier for spin-polarized tunneling

M. Bibes, M. Bowen, A. Barthélémy, A. Anane, K. Bouzehouane, C. Carrétéro, E. Jacquet, J.-P. Contour, and O. Durand

Appl. Phys. Lett. 82, 3269 (2003); http://dx.doi.org/10.1063/1.1568159 (3 pages) | Cited 22 times

Online Publication Date: 6 May 2003

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We report on the elaboration and characterization of tunnel junctions based on La2/3Sr1/3MnO3 and TiO2. The structural analysis shows that TiO2 grows epitaxially in the anatase phase and forms flat interfaces with the adjacent layers. Resistance maps of a La2/3Sr1/3MnO3/TiO2 bilayer reveal a homogeneous resistance level. After patterning tunnel junctions, we obtain a large positive tunneling magnetoresistance (TMR) at low temperature for La2/3Sr1/3MnO3/TiO2/La2/3Sr1/3MnO3 junctions and a negative TMR in the case of La2/3Sr1/3MnO3/TiO2/Co. This negative TMR reflects a negative spin polarization of Co at the interface with TiO2, in analogy with recent experimental results for the Co/SrTiO3 interface. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
75.50.Cc Other ferromagnetic metals and alloys
75.50.Dd Nonmetallic ferromagnetic materials
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Submicron electrical current density imaging of embedded microstructures

B. D. Schrag and Gang Xiao

Appl. Phys. Lett. 82, 3272 (2003); http://dx.doi.org/10.1063/1.1570499 (3 pages) | Cited 13 times

Online Publication Date: 6 May 2003

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We have developed a scanning magnetic microscopy technique for noninvasively imaging submicron magnetic fields from embedded microscopic electrical circuits. We are able to extract from the field data a complete profile of current densities using a mathematical algorithm. As an example, we provide current density images of micron-scale passivated conductors undergoing electromigration. © 2003 American Institute of Physics.
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07.79.-v Scanning probe microscopes and components
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.55.Ge Magnetometers for magnetic field measurements
85.30.De Semiconductor-device characterization, design, and modeling

Nondestructive determination of current–voltage characteristics of superconducting films by inductive critical current density measurements as a function of frequency

Hirofumi Yamasaki, Yasunori Mawatari, and Yoshihiko Nakagawa

Appl. Phys. Lett. 82, 3275 (2003); http://dx.doi.org/10.1063/1.1571657 (3 pages) | Cited 26 times

Online Publication Date: 6 May 2003

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A nondestructive inductive method was developed to determine the current–voltage characteristics of superconducting films by measuring the critical current density Jc as a function of the frequency of ac magnetic fields. In well-known inductive methods that measure the Jc distribution of large-area films, Jc is measured at a frequency and the electric field E induced in the superconductor is proportional to the frequency; therefore, the E versus current density relation can be determined by measuring Jc at various frequencies. Current–voltage characteristics of YBa2Cu3O7 films measured by this method agree well with those determined by measuring magnetic-field-sweep rate dependence of magnetization. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Curie temperature and carrier concentration gradients in epitaxy-grown Ga1−xMnxAs layers

A. Koeder, S. Frank, W. Schoch, V. Avrutin, W. Limmer, K. Thonke, R. Sauer, A. Waag, M. Krieger, K. Zuern, P. Ziemann, S. Brotzmann, and H. Bracht

Appl. Phys. Lett. 82, 3278 (2003); http://dx.doi.org/10.1063/1.1573369 (3 pages) | Cited 19 times

Online Publication Date: 6 May 2003

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We report on detailed investigations of the electronic and magnetic properties of ferromagnetic Ga1−xMnxAs layers, which have been fabricated by low-temperature molecular-beam epitaxy. Superconducting quantum interference device measurements reveal a decrease of the Curie temperature from the surface to the Ga1−xMnxAs/GaAs interface. While high-resolution x-ray diffraction clearly shows a homogeneous Mn distribution, a pronounced decrease of the carrier concentration from the surface towards the Ga1−xMnxAs/GaAs interface has been found by Raman spectroscopy as well as electrochemical capacitance–voltage profiling. The gradient in Curie temperature seems to be a general feature of Ga1−xMnxAs layers grown at low temperature. Possible explanations are discussed. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ey III-V semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
68.55.Nq Composition and phase identification
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Growth and characterization of sputtered epitaxial γ′Fe4N and NbN films and bilayers using electron backscatter diffraction patterns and magnetometry

R. Loloee, K. R. Nikolaev, and W. P. Pratt

Appl. Phys. Lett. 82, 3281 (2003); http://dx.doi.org/10.1063/1.1573356 (3 pages) | Cited 7 times

Online Publication Date: 6 May 2003

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Epitaxial single-crystal ferromagnetic Fe4N films (γ′ phase of iron nitride), nonmagnetic NbN films, and NbN/Fe4N bilayers were grown on MgO(100) substrates by sputter deposition in N2 gas. Electron backscatter diffraction patterns were used to characterize the structural properties including the relative crystallographic orientation of the sputter deposited Fe4N and NbN films with respect to the substrate and each other. Superconducting quantum interference device magnetometry was used to study the in-plane uniaxial anisotropy and determine the directions of the easy axes in ferromagnetic Fe4N films. © 2003 American Institute of Physics.
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81.15.Cd Deposition by sputtering
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology

(001) oriented FePt–Ag composite nanogranular films on amorphous substrate

K. Kang, Z. G. Zhang, C. Papusoi, and T. Suzuki

Appl. Phys. Lett. 82, 3284 (2003); http://dx.doi.org/10.1063/1.1574401 (3 pages) | Cited 22 times

Online Publication Date: 6 May 2003

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By annealing the multilayer film with a stack structure of MgO 10 nm/Ag 20 nm/[FePt x nm/Ag 5 nm]5 at 550 °C for 1 h, (001)-oriented L10 FePt nanograins with high perpendicular magnetic anisotropy are obtained on an amorphous substrate. The 20-nm Ag underlayer plays an important role in improving (001) texture of FePt and decreasing the fct FePt ordering temperature. The switching volume and uniaxial magnetic anisotropy constant Ku of FePt–Ag composite films with a controllable FePt grain size are obtained by fitting the coercivity dependence on magnetic field sweeping rate employing coherent rotation model, taking into account the easy axis distribution. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Mapping electron flow using magnetic force microscopy

R. Yongsunthon, A. Stanishevsky, E. D. Williams, and P. J. Rous

Appl. Phys. Lett. 82, 3287 (2003); http://dx.doi.org/10.1063/1.1573349 (3 pages) | Cited 9 times

Online Publication Date: 6 May 2003

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Electron flow around defects in conductors is highly dependent on the local geometry of the defect. The sensitivity of magnetic force microscopy (MFM) for the direct imaging of such variations at the submicron scale has been tested using model defect structures fabricated in gold lines by focused ion beam milling. The corresponding MFM images, taken with current densities of ∼ 106 A/cm2, have qualitatively different features near different defects, with stronger and more localized signal for the more highly curved current pathways. Quantitative analysis, via image deconvolution followed by inversion using the Biot–Savart law, yields parallel and perpendicular components of the current densities in the vicinity of each defect structure. MFM imagery clearly resolves differences in the electron flow around defects of similar size but differing geometry. © 2003 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
68.37.Rt Magnetic force microscopy (MFM)

External magnetic field effect on third-harmonic generation in Bi, Al-doped yttrium iron garnet

Jusuke Shimura, Shin-ichi Ohkoshi, and Kazuhito Hashimoto

Appl. Phys. Lett. 82, 3290 (2003); http://dx.doi.org/10.1063/1.1574843 (3 pages) | Cited 4 times

Online Publication Date: 6 May 2003

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The magnetic field effect on the third-harmonic generation (THG) in a Y1.5Bi1.5Fe3.8Al1.2O12 magnetic film was investigated. Applying a longitudinal external magnetic field rotated the polarization plane of the TH wave. The TH rotation angle was 4.1° at 2.67 eV (incoming wave: 0.89 eV) in a magnetic field of 1.0 kOe. Based on the symmetry analysis, the TH rotation was understood by an apparition of a magnetic term of χyxxx(3)(M) in a third-order nonlinear optical susceptibility. © 2003 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Nk Insulators
78.20.Ls Magneto-optical effects
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
42.79.Wc Optical coatings
42.65.An Optical susceptibility, hyperpolarizability
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