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24 Oct 2005

Volume 87, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 87, 172506 (2005); http://dx.doi.org/10.1063/1.2120911 (3 pages)

T. Kimura, Y. Otani, and J. Hamrle
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Semiconductor-metal hybrid structures as local magnetic-field probes: Magnetoresistance and spatial sensitivity profile

Matthias Holz, Oliver Kronenwerth, and Dirk Grundler

Appl. Phys. Lett. 87, 172501 (2005); http://dx.doi.org/10.1063/1.2108122 (3 pages) | Cited 2 times

Online Publication Date: 17 October 2005

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Tailored nonmagnetic semiconductor-metal hybrid structures exhibit a large magnetoresistance effect in a homogeneous magnetic field. This is the so-called extraordinary magnetoresistance effect. Here, we study numerically the magnetoresistance of such hybrid structures in the inhomogeneous field of a magnetic dot. Surprisingly, the four-point resistance R versus magnetic field B changes its symmetry if compared to the case of a homogeneous field and is strongly dependent on the position of the local magnetic field. Interestingly, the active device area is not defined by the voltage probe separation, but by the positioning of voltage probes and current leads. We find a magnetoresistance effect as large as 18% although only 1/60 of the device area is subject to a small magnetic field of ±50 mT. These results are promising for sensing magnetic-field distributions in the nanoscale regime such as the stray fields of magnetic recording media.
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73.40.Ns Metal-nonmetal contacts
72.20.My Galvanomagnetic and other magnetotransport effects

Epitaxial growth and properties of Zn1−xVxO diluted magnetic semiconductor thin films

S. Ramachandran, A. Tiwari, J. Narayan, and J. T. Prater

Appl. Phys. Lett. 87, 172502 (2005); http://dx.doi.org/10.1063/1.2112185 (3 pages) | Cited 25 times

Online Publication Date: 17 October 2005

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Here we report systematic studies on the epitaxial growth and properties of Zn1−xVxO[x=0.001-0.2] thin films deposited onto sapphire c-plane single crystals. The thin films were deposited using pulsed laser deposition technique and were found to be epitaxial in nature. X-ray diffraction and high resolution transmission electron microscopy were employed to study the epitaxial relations of Zn1−xVxO with the sapphire substrate and electron energy loss spectroscopy was used to establish the bonding characteristics and oxidation states of vanadium inside the ZnO host. The main emphasis is on the magnetic properties of this system taking into consideration the phase purity and microstructural characteristics of these films. Our results show that the Zn1−xVxO system, with V in zinc substitutional sites, does not exhibit any signature of ferromagnetism, both at room temperature as well as at lower temperatures down to 10 K.
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81.05.Hd Other semiconductors
75.50.Pp Magnetic semiconductors
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy

Anisotropic magnetoresistance and spin polarization of La0.7Sr0.3MnO3/SrTiO3 superlattices

L. M. Wang and Chih-Chian Guo

Appl. Phys. Lett. 87, 172503 (2005); http://dx.doi.org/10.1063/1.2112167 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2005

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The crystalline structure, anisotropic magnetoresistance (AMR), and magnetization of La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices grown by a rf sputtering system are systematically analyzed to study the spin polarization of manganite at interfaces. The presence of positive low-temperature AMR in LSMO/STO superlattices implies that two bands of majority and minority character contribute to the transport properties, leading to a reduced spin polarization. Furthermore, the magnetization of superlattices follows the T3/2 law and decays more quickly as the thickness ratio dSTO/dLSMO increases, corresponding to a reduced exchange coupling. The results clearly show that the spin polarization is strongly correlated with the influence of interface-induced strain on the structure.
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75.47.Lx Magnetic oxides
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Mk Spin transport through interfaces
68.65.Ac Multilayers
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Cd Superlattices
73.21.Cd Superlattices
61.66.Fn Inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
75.30.Et Exchange and superexchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions
71.20.Ps Other inorganic compounds

Current localization and enhanced percolative low-field magnetoresistance in disordered half metals

Sheng Ju, Tian-Yi Cai, and Z. Y. Li

Appl. Phys. Lett. 87, 172504 (2005); http://dx.doi.org/10.1063/1.2084318 (3 pages) | Cited 9 times

Online Publication Date: 19 October 2005

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By modeling the magnetotransport in disordered half metals onto a random resistor network, we have performed numerical simulations on the low-field magnetoresistance (LFMR) and the current distribution in the network. It is found that there is a close relationship between the magnitude of LFMR and the current morphology. LFMR increases with the increase of current localization. In the limit of strong disorder, a quasi-one-dimensional transport channel forms and LFMR reaches its maximum. Compared with the previous two-component (metal/insulator) percolative scenario for colossal magnetoresistance in phase-separated manganites, such a current percolation transition gives further understanding of the magnetotransport in disordered half metals.
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75.47.Lx Magnetic oxides
72.60.+g Mixed conductivity and conductivity transitions
64.75.-g Phase equilibria

Well-aligned Mn-doped ZnO nanowires synthesized by a chemical vapor deposition method

J. J. Liu, M. H. Yu, and W. L. Zhou

Appl. Phys. Lett. 87, 172505 (2005); http://dx.doi.org/10.1063/1.2084321 (3 pages) | Cited 50 times

Online Publication Date: 19 October 2005

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Well-aligned diluted magnetic semiconductor Zn1−xMnxO nanowires have been fabricated at 850 °C from a self-formed ZnO substrate using a chemical vapor deposition method. The as-synthesized Mn-doped ZnO nanowires were characterized by field emission scanning electron microscopy and transmission electron microscopy (TEM). The well-aligned nanowires are single crystalline and are perpendicularly grown along the c axis. Electron energy x-ray dispersive analysis, x-ray diffraction spectrometry, and TEM analysis clearly showed that Mn was doped both in the ZnO nanowires and substrate. Ferromagnetic ordering of the as-synthesized Zn1−xMnxO nanowire arrays was observed at 5 K with Curie temperature of 44 K by superconducting quantum interference device measurement.
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81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
75.50.Pp Magnetic semiconductors
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
75.75.-c Magnetic properties of nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Determination of magnetic vortex chirality using lateral spin-valve geometry

T. Kimura, Y. Otani, and J. Hamrle

Appl. Phys. Lett. 87, 172506 (2005); http://dx.doi.org/10.1063/1.2120911 (3 pages) | Cited 15 times

Online Publication Date: 19 October 2005

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We demonstrate the determination of the vortex chirality using a nonlocal spin-valve measurement technique in a lateral spin valve consisting of a Permalloy (Py) disk 1 μm in diameter and a Py wire 100 nm in width. The vortex chirality is determined under two probe configurations; the disk as the current probe and the disk as the voltage probe. The vortex chirality is found to depend on the probe configuration because of the current-induced Oersted field.
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75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Josephson devices for controllable flux qubit and interqubit coupling

C. Granata, B. Ruggiero, M. Russo, A. Vettoliere, V. Corato, and P. Silvestrini

Appl. Phys. Lett. 87, 172507 (2005); http://dx.doi.org/10.1063/1.2115083 (3 pages) | Cited 5 times

Online Publication Date: 19 October 2005

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We present niobium-based Josephson devices as prototypes for applications to quantum computation with flux qubits. The most interesting feature of this device is the use of a Josephson vertical interferometer for a fine tuning of flux qubit and interquibit coupling. These devices allow a control of the off-diagonal Hamiltonian terms of flux qubit and of the flux transfer function of a superconducting transformer. In the vertical interferometer, the Josephson current is precisely modulated from a maximum to zero with fine control and precision by a small transversal magnetic field parallel to the radio-frequency superconducting loop plane and to the flux transformer.
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85.25.Cp Josephson devices
03.67.Lx Quantum computation architectures and implementations

Effect of stray field on local spin modes in exchange-biased magnetic tunnel junction elements

J. H. H. Rietjens, C. Józsa, W. J. M. de Jonge, B. Koopmans, and H. Boeve

Appl. Phys. Lett. 87, 172508 (2005); http://dx.doi.org/10.1063/1.2117614 (3 pages) | Cited 1 time

Online Publication Date: 20 October 2005

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We report on the detection of localized spin modes in a multilayered spintronic device by means of time-resolved scanning Kerr microscopy. Measurements on this 13×9 μm2 exchange-biased magnetic tunnel junction element at different applied bias fields indicate a strong effect of the stray field from the pinned CoFe layer on the magnetization dynamics in the free NiFe layer. This view is supported by micromagnetic simulations, which also show that the dynamics can be attributed to the specific shape of the internal magnetic field in the element.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Influence of surface/interface roughness and grain size on magnetic property of Fe/Co bilayer

Deeder Aurongzeb, K. Bhargava Ram, and Latika Menon

Appl. Phys. Lett. 87, 172509 (2005); http://dx.doi.org/10.1063/1.2119427 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2005

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In this work, we report the influence of surface roughness and cluster size on coercivity of Fe/Co bilayer. Coercivity was tuned by thermal annealing. No systematic trend was found for temperature dependent annealing. However, after annealing at 350 °C, we find systematic increase in coercivity with anneal time. For as-deposited film, we find unusually low coercivity (0.39 Oe). By increasing annealing time, coercivity was tuned to values as high as 600 Oe. Surface characterization using atomic force microscopy showed uniform clusters at this temperature after 2 h of annealing. The observed magnetic properties are discussed in terms of cluster size and surface/interface roughness.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
68.47.De Metallic surfaces
68.37.Ps Atomic force microscopy (AFM)
81.40.Gh Other heat and thermomechanical treatments

Theoretical simulation and experimental study on resistivity properties of mixed-phase La2/3Ca1/3MnO3 thin films

Qing-li Zhou, Kun Zhao, Kui-juan Jin, Dong-yi Guan, Hui-bin Lu, Zheng-hao Chen, Guo-zhen Yang, Alan Li, and H. K. Wong

Appl. Phys. Lett. 87, 172510 (2005); http://dx.doi.org/10.1063/1.2119413 (3 pages) | Cited 8 times

Online Publication Date: 21 October 2005

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The theoretical simulation and experimental study are reported on the metal-to-insulator transition, thermal hysteresis behavior, magnetic-field-induced reduction, and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 thin films deposited on SrTiO3 (001)-oriented substrates tilted by 10° towards the [010] direction. The simulated results obtained by using a random network model based on phase separation scenario are in quantitative agreement with our experimental data and indicate that tilting (applying magnetic field) can increase (decrease) the scatterings and the activation energy, resulting in enhancement (reduction) of resistivity. All those results suggest that the intrinsic inhomogeneity and the lattice structure play the significant roles in the electrical conductivity and anisotropic transport properties.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

Growth and magnetism of Cr-doped InN

R. Rajaram, A. Ney, G. Solomon, J. S. Harris, R. F. C. Farrow, and S. S. P. Parkin

Appl. Phys. Lett. 87, 172511 (2005); http://dx.doi.org/10.1063/1.2115085 (3 pages) | Cited 7 times

Online Publication Date: 21 October 2005

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We present structural and magnetic characterization of Cr-doped InN films grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Low-temperature GaN buffer layers grown by metalorganic vapor-phase epitaxy were used to accommodate the large lattice mismatch between InN and sapphire. A high n-type carrier concentration of 1.5×1020 cm−3 was measured in InN films with 3% Cr doping. Films of this type, with high structural perfection, as measured in situ, with reflection high-energy electron diffraction, exhibit a well-defined in-plane magnetic hysteresis loop for temperatures varying from 5 to 300 K. Thus, we show evidence of magnetic order in Cr-doped InN.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.uj III-V and II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
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