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3 Jun 2002

Volume 80, Issue 22, pp. 4085-4270

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Local control of dynamic nuclear polarization in quantum Hall devices

Tomoki Machida, Tomoyuki Yamazaki, and Susumu Komiyama

Appl. Phys. Lett. 80, 4178 (2002); http://dx.doi.org/10.1063/1.1483910 (3 pages) | Cited 18 times

Online Publication Date: 23 May 2002

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We manipulate and detect local nuclear spin polarization in integer quantum Hall (IQH) systems using micrometal strips fabricated on top of Al0.3Ga0.7As/GaAs Hall bar devices. The radio-frequency (rf) magnetic fields generated by transmitting rf electrical currents through the micrometal strips causes nuclear magnetic resonance in a limited region along IQH edge channels, and resulting changes in the nuclear spin polarization are detected via Hall resistance of the devices. © 2002 American Institute of Physics.
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73.43.-f Quantum Hall effects
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

Room-temperature observation of high-spin polarization of epitaxial CrO2(100) island films at the Fermi energy

Yu. S. Dedkov, M. Fonine, C. König, U. Rüdiger, G. Güntherodt, S. Senz, and D. Hesse

Appl. Phys. Lett. 80, 4181 (2002); http://dx.doi.org/10.1063/1.1482142 (3 pages) | Cited 41 times

Online Publication Date: 23 May 2002

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Epitaxial CrO2(100) island films have been grown on TiO2(100) substrates by a chemical-vapor deposition technique. Well-controlled surface and interface properties of the CrO2(100) films were confirmed by scanning tunneling microscopy and transmission electron microscopy, respectively. Spin- and angle-resolved photoemission spectroscopy at room temperature revealed an energy gap of about 2 eV below Fermi level EF for spin-down electrons and a spin polarization of about +95% at EF. After extended sputtering, the spin polarization can be recovered from about +10% up to +85% upon annealing. © 2002 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
68.55.-a Thin film structure and morphology
72.25.-b Spin polarized transport
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.70.Ak Magnetic properties of monolayers and thin films
79.60.Dp Adsorbed layers and thin films
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Ps Other inorganic compounds

Characterization of superconducting structures designed for qubit realizations

E. Il’ichev, Th. Wagner, L. Fritzsch, J. Kunert, V. Schultze, T. May, H. E. Hoenig, H. G. Meyer, M. Grajcar, D. Born, W. Krech, M. V. Fistul, and A. M. Zagoskin

Appl. Phys. Lett. 80, 4184 (2002); http://dx.doi.org/10.1063/1.1481988 (3 pages) | Cited 21 times

Online Publication Date: 23 May 2002

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We implement the impedance measurement technique in order to characterize superconducting structures designed for applications in quantum computing. We report an experimental study of the circuit consisting of three small Josephson junctions incorporated in a low-inductance superconducting loop. Measurements of the circuit response to an applied weak ac bias as a function of the external magnetic flux ϕe yield complete information on the properties of the circuit. We found that the system displays two metastable states. From experimental data, we have determined the magnetic field dependent Josephson energy U(ϕe) of these states, the potential barrier ΔU between these states, as well as the difference of the critical currents of the junction in the loop. © 2002 American Institute of Physics.
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85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
85.25.Cp Josephson devices
03.67.Lx Quantum computation architectures and implementations
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
84.30.Sk Pulse and digital circuits

Room-temperature ferromagnetism in Cr-doped GaN single crystals

Sang Eon Park, Hyeon-Jun Lee, Yong Chan Cho, Se-Young Jeong, Chae Ryong Cho, and Sunglae Cho

Appl. Phys. Lett. 80, 4187 (2002); http://dx.doi.org/10.1063/1.1483115 (3 pages) | Cited 111 times

Online Publication Date: 23 May 2002

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We report on the discovery of a room-temperature ferromagnetism in Cr-doped GaN single crystals with a Tc = 280 K. The addition of Cr into GaN single crystals grown by the flux method induces the lattice constant increase due to the larger Cr atomic radius. In x-ray photoelectron spectroscopy measurement, Cr 2p3/2 core-level exhibited spectra near 575.7 eV. This binding energy is similar to the reported value of CrN. The coercive field by magnetization–magnetic field (M–H) hysteresis curve at 250 K was 54 Oe. We verified the presence of ferromagnetic transition in the temperature dependence of the electrical resistance measurements. We discuss the ferromagnetic ordering in Cr-doped GaN bulk single crystals excluding the contribution of the substrate crystal structure. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Ea III-V semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.66.Fn Inorganic compounds

Magnetic force microscopy observation of antivortex core with perpendicular magnetization in patterned thin film of permalloy

K. Shigeto, T. Okuno, K. Mibu, T. Shinjo, and T. Ono

Appl. Phys. Lett. 80, 4190 (2002); http://dx.doi.org/10.1063/1.1483386 (3 pages) | Cited 35 times

Online Publication Date: 23 May 2002

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The cross-tie wall is a kind of magnetic domain wall composed of a main straight wall and crossing subwalls and observed in magnetic thin films. This wall contains two kinds of magnetic vortex structures: “circular vortex” and “antivortex.” At the cores of both vortices, the existence of a spot with perpendicular magnetization has been theoretically predicted. We have detected the perpendicular magnetization spots at each vortex core and identified the direction of it by applying magnetic force microscopy imaging to cross-tie walls in patterned rectangular thin permalloy (Ni80Fe20) films. We also fabricated magnetic structures that contain only antivortex by engineering the shape of thin films. © 2002 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.37.Rt Magnetic force microscopy (MFM)

Magnetic moment and anisotropy in FenCom clusters

J. Kortus, T. Baruah, M. R. Pederson, C. Ashman, and S. N. Khanna

Appl. Phys. Lett. 80, 4193 (2002); http://dx.doi.org/10.1063/1.1482793 (3 pages) | Cited 12 times

Online Publication Date: 23 May 2002

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Electronic structure calculations of FenCom (n+m = 5 and 13) are used to examine the effects of alloying on the magnetic moment and magnetic anisotropies. Our density-functional studies show that many mixed clusters have moments comparable to or higher than the pure clusters. The mixed clusters, however, have very low anisotropies and could be ideal as soft magnetic materials. It is shown that shape, composition, and compositional ordering must be considered for optimization of anisotropy energies. © 2002 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.10.Lp Band and itinerant models
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.40.Mg Numerical simulation studies

Superconductivity in thin-film YBa2Cu3O7−δ/La0.7Ca0.3MnO3 bilayers

M. D. Allsworth, R. A. Chakalov, M. S. Colclough, P. Mikheenko, and C. M. Muirhead

Appl. Phys. Lett. 80, 4196 (2002); http://dx.doi.org/10.1063/1.1480888 (3 pages) | Cited 10 times

Online Publication Date: 23 May 2002

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We report the influence of the magnetic state of thin films of La0.7Ca0.3MnO3 (LCMO) on the superconducting order parameter in LCMO/YBa2Cu3O7−δ (YBCO) thin-film bilayers. We find that the number density of Cooper pairs is enhanced at the coercive field of the LCMO layer relative to that where the magnetic moment is saturated. This effect is at most ∼ 10% and is only observable within a few degrees of the superconducting transition temperature. Experiments with thin SrTiO3 layers between the LCMO and YBCO layers provide strong evidence that the effect is a consequence of the spin-polarized nature of the electrons at the interface, rather than a direct magnetic effect. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.78.Fk Multilayers, superlattices, heterostructures
74.20.Fg BCS theory and its development
74.50.+r Tunneling phenomena; Josephson effects
72.25.Mk Spin transport through interfaces
74.10.+v Occurrence, potential candidates
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

Detection of a single magnetic microbead using a miniaturized silicon Hall sensor

Pierre-A. Besse, Giovanni Boero, Michel Demierre, Vincent Pott, and Radivoje Popovic

Appl. Phys. Lett. 80, 4199 (2002); http://dx.doi.org/10.1063/1.1483909 (3 pages) | Cited 89 times

Online Publication Date: 23 May 2002

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Using a highly sensitive silicon Hall sensor fabricated in a standard complementary metal–oxide–semiconductor (CMOS) technology, we detect a single magnetic microbead of 2.8 μm in diameter. The miniaturized sensor has an active area of 2.4×2.4 μm2, a sensitivity of 175 V/AT and a resistance of 8.5 kΩ. Two detection methods, both exploiting the superparamagnetic behavior of the bead, are experimentally tested and their performances are compared. This work opens the way to the fabrication of low cost microsystems for biochemical applications based on the use of dense arrays of silicon Hall sensors and CMOS electronics. © 2002 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.50.Tt Fine-particle systems; nanocrystalline materials
87.80.-y Biophysical techniques (research methods)
72.20.My Galvanomagnetic and other magnetotransport effects

Transport properties of CrO2 (110) films grown on TiO2 buffered Si substrates by chemical vapor deposition

S. J. Liu, J. Y. Juang, K. H. Wu, T. M. Uen, Y. S. Gou, and J.-Y. Lin

Appl. Phys. Lett. 80, 4202 (2002); http://dx.doi.org/10.1063/1.1481534 (3 pages) | Cited 8 times

Online Publication Date: 23 May 2002

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Epitaxial CrO2 (110)-oriented films were fabricated on Si (100) substrates buffered by rutile TiO2 derived from oxidation of a pulsed-laser-deposited TiN layer. The epitaxial films of CrO2 were prepared by chemical vapor deposition in a two-zone furnace with oxygen flow from a CrO3 precursor. The transport measurements show that the CrO2 films are metallic with a Curie temperature of about 380 K. The temperature dependence of resistivity was best described by a phenomenological expression ρ(T) = ρ0+AT2e(−Δ/T) over the range of 5–350 K with Δ = 94 K. The magnetic measurements show the in-plane coercive fields are about 30 and 60 Oe at 300 and 5 K, respectively. The temperature dependent spontaneous magnetization follows Bloch’s T3/2 law and the slope suggests a critical wavelength of λΔ ∼ 30.6 Å beyond which spin-flip scattering becomes important. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Dd Nonmetallic ferromagnetic materials
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