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2 Apr 2007

Volume 90, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 142110 (2007); http://dx.doi.org/10.1063/1.2720640 (3 pages)

M. T. Björk, O. Hayden, H. Schmid, H. Riel, and W. Riess
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Hole distribution and local structure in La2−xSrxCuO4

F. L. Tang and X. Zhang

Appl. Phys. Lett. 90, 142501 (2007); http://dx.doi.org/10.1063/1.2719024 (3 pages) | Cited 2 times

Online Publication Date: 2 April 2007

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Atomistic simulation has been performed on La2−xSrxCuO4 to investigate its hole distribution and local structure in real space lattice. It is found that the holes introduced by Sr doping are more energetically favorable to form stripes than to be disordered. The authors verify two types of hole-stripe models (vertical and diagonal domain walls) and propose some other possible types of hole-stripe models, which are quarter or half filled. The local structure of hole stripes is found to be different from the average structure. Sr2+ ions are also found to have a thermodynamics tendency of ordering.
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74.72.-h Cuprate superconductors
74.25.F- Transport properties
74.25.Dw Superconductivity phase diagrams
74.25.Bt Thermodynamic properties

Magnetic properties of n-type Cu-doped ZnO thin films

D. L. Hou, X. J. Ye, H. J. Meng, H. J. Zhou, X. L. Li, C. M. Zhen, and G. D. Tang

Appl. Phys. Lett. 90, 142502 (2007); http://dx.doi.org/10.1063/1.2719034 (3 pages) | Cited 55 times

Online Publication Date: 2 April 2007

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A series of n-type Zn1−xCuxO (x = 0.02, 0.06, 0.10, and 0.12) films was prepared using direct current reactive magnetron sputtering. Magnetic measurements indicate that all the films are ferromagnetic at room temperature and the moment per Cu ion decreases with increasing copper concentration and nitrogen doping. The observed magnetic moment was 1.8 μB/Cu for Zn0.98Cu0.02O film and the transition temperature of about 350 K decreased to 320 K due to nitrogen doping. It can be concluded that itinerant electrons play an important role in ferromagnetism. The resistivity increased with increasing copper concentration and nitrogen doping. The anomalous Hall effect has been found for ferromagnetic materials.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ga II-VI semiconductors

Remote-control spin filtering through a T-type structure

X. Y. Feng, J. H. Jiang, and M. Q. Weng

Appl. Phys. Lett. 90, 142503 (2007); http://dx.doi.org/10.1063/1.2719174 (3 pages) | Cited 5 times

Online Publication Date: 2 April 2007

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The authors propose a spin filter scheme using a T-stub waveguide. By applying a moderate magnetic field at the tip of the sidearm, this device can produce both large electric and spin currents. The direction and polarization of the output spin current can be further adjusted electronically by a remote gate which tunes the length of the sidearm. The device is robust against the disorder.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Near-field microwave probe for local ferromagnetic resonance characterization

Dragos I. Mircea and T. W. Clinton

Appl. Phys. Lett. 90, 142504 (2007); http://dx.doi.org/10.1063/1.2719241 (3 pages) | Cited 12 times

Online Publication Date: 2 April 2007

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A local ferromagnetic resonance (FMR) technique using a thin-film microwave probe fabricated on coaxial transmission line is presented. Some key features of this probe are its micron-scale size coupled with broadband FMR characterization and mobility: a small area of any location on a magnetic medium can be probed. Permeability of Permalloy (Py) films has been measured, where the authors extract physical parameters, such as FMR frequency, anisotropy field, damping, and spin wave exchange constant, in excellent agreement with independent measurements. Samples of arbitrary shape and size can be measured with a spatial resolution that scales with the size of the probe “tip.”
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75.50.Bb Fe and its alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Depression of Curie temperature by surface structural phase transition

H. Y. Ho, Y. J. Chen, E. J. Hwang, S. K. Yu, and C. S. Shern

Appl. Phys. Lett. 90, 142505 (2007); http://dx.doi.org/10.1063/1.2719630 (3 pages) | Cited 3 times

Online Publication Date: 2 April 2007

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The comparative study in structural properties for the mirror systems, 1 ML Ni/1 ML Co/Pt(111) and 1 ML Co/1 ML Ni/Pt(111) surface ordered alloys, reveals a structural phase transition from NixCo1−xPt to NixCo1−xPt3 ordered surface alloy when the annealing temperature is between 750 and 800 K. The Curie temperature speeds up to decrease when the surface structure changes from NixCo1−xPt to NixCo1−xPt3. The value of critical exponent β near the Curie point crosses from a two-dimensional-like magnetic phase to a three-dimensional-like one after the phase transition. From the composition dependence of the Curie temperature, one can adjust the Curie temperatures of the surface alloy by controlling the annealing temperature.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.35.Rh Phase transitions and critical phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Gh Other heat and thermomechanical treatments
64.60.F- Equilibrium properties near critical points, critical exponents

Magnetoresistance after initial demagnetization in La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3 magnetic tunnel junctions

E. T. Wertz and Q. Li

Appl. Phys. Lett. 90, 142506 (2007); http://dx.doi.org/10.1063/1.2718481 (3 pages) | Cited 7 times

Online Publication Date: 3 April 2007

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Magnetic tunnel junctions were fabricated from La0.67Sr0.33MnO3 (LSMO)/SrTiO3/La0.67Sr0.33MnO3 heterostructures. Junctions initially demagnetized at 5 K with an in-plane magnetic field showed larger tunneling magnetoresistance (TMR) and sharper switching than standard TMR scans. Magnetoresistive switching from the demagnetized state was stable in fields <80 G yielding a TMR of 475% and a ΔMR/ΔH ≈ 200%/G. Changes in resistance achievable at <500 G yielded a TMR of ≈ 850%. A similar TMR was seen when rotating the magnetic field from an in-plane to out-of-plane orientation. The demagnetized high resistance state may indicate that the LSMO layers preferentially choose a more efficient opposite magnetic domain alignment.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Gk Colossal magnetoresistance
75.60.Ch Domain walls and domain structure
75.50.Dd Nonmetallic ferromagnetic materials

Kinetic self-organization of trenched templates for the fabrication of versatile ferromagnetic nanowires

B. Borca, O. Fruchart, Ph. David, A. Rousseau, and C. Meyer

Appl. Phys. Lett. 90, 142507 (2007); http://dx.doi.org/10.1063/1.2718510 (3 pages) | Cited 4 times

Online Publication Date: 4 April 2007

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The authors have self-organized versatile magnetic nanowires, i.e., with variable period and adjustable magnetic anisotropy energy (MAE). First, using the kinetic roughening of W(110), uniaxial templates of trenches were grown on commercial sapphire wafers. Unlike most templates used for self-organization, those have a variable period; 4–12 nm are demonstrated here. Fe deposition then results in the formation of wires in the trenches. The magnitude of MAE could be engineered up or down by changing the capping layer or underlayer, in turn affecting the mean superparamagnetic temperature, raised to 175 K so far.
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81.16.Dn Self-assembly
75.50.Bb Fe and its alloys
68.65.La Quantum wires (patterned in quantum wells)
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials

Localized steady-state domain wall oscillators

J. He and S. Zhang

Appl. Phys. Lett. 90, 142508 (2007); http://dx.doi.org/10.1063/1.2719646 (3 pages) | Cited 18 times

Online Publication Date: 4 April 2007

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The authors predict a spatially localized magnetic domain wall oscillator upon the application of an external magnetic field and a dc electric current. The amplitude and frequency of the oscillator can be controlled by the field and/or the current. The resulting oscillator could be used as an effective microwave source for information storage application.
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75.60.Ch Domain walls and domain structure
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Planar Hall effect and magnetic anisotropy in epitaxially strained chromium dioxide thin films

S. T. B. Goennenwein, R. S. Keizer, S. W. Schink, I. van Dijk, T. M. Klapwijk, G. X. Miao, G. Xiao, and A. Gupta

Appl. Phys. Lett. 90, 142509 (2007); http://dx.doi.org/10.1063/1.2715442 (3 pages) | Cited 6 times

Online Publication Date: 4 April 2007

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We have measured the in-plane anisotropic magnetoresistance of 100 nm thick CrO2 thin films at liquid He temperatures. In low magnetic fields H, both the longitudinal and the transverse (planar Hall) resistance show abrupt switches, which characteristically depend on the orientation of H. All the experimental findings consistently demonstrate that the magnetic anisotropy in these CrO2 thin films is biaxial. We show that the biaxial magnetic anisotropy is due to epitaxial coherency strain, and that it naturally explains the complex magnetic switching behavior reported recently in CrO2 films with thicknesses of 50 nm ⩽ d ⩽ 250 nm.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.60.-d Domain effects, magnetization curves, and hysteresis

Oscillatory interlayer exchange coupling in epitaxial Co2MnSi/Cr/Co2MnSi trilayers

H. Wang, A. Sato, K. Saito, S. Mitani, K. Takanashi, and K. Yakushiji

Appl. Phys. Lett. 90, 142510 (2007); http://dx.doi.org/10.1063/1.2719606 (3 pages) | Cited 16 times

Online Publication Date: 5 April 2007

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Interlayer exchange coupling (IEC) in trilayers, which consist of a full Heusler Co2MnSi (CMS) phase as ferromagnetic layers separated by a Cr spacer layer, has been investigated. The shape of magnetization loops shows unusual oscillatory behavior with the thickness of Cr. The oscillation period is about 3.3–3.5 nm. The charecteristics of magnetization curves show that 90° coupling plays a dominant role in IEC between CMS layers. Moreover, the strength of 90° coupling turns out to be very high (up to −1.85 ergs/cm2) around the first oscillation peak.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Superconductivity in doped cubic silicon: An ab initio study

E. Bourgeois and X. Blase

Appl. Phys. Lett. 90, 142511 (2007); http://dx.doi.org/10.1063/1.2719663 (3 pages) | Cited 12 times

Online Publication Date: 5 April 2007

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The authors study within a first-principles approach the band structure, vibrational modes, and electron-phonon coupling in boron-, aluminum-, and phosphorus-doped silicon in the diamond phase. Their results provide evidences that the recently discovered superconducting transition in boron-doped cubic silicon, with a transition temperature of ∼ 0.34 K, can be explained within a standard phonon-mediated mechanism. The importance of lattice compression and dopant related stretching modes are emphasized. The authors find that TC can be increased by one order of magnitude by adopting aluminum doping instead of boron.
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74.10.+v Occurrence, potential candidates
74.20.Fg BCS theory and its development
74.25.Jb Electronic structure (photoemission, etc.)
74.25.Kc Phonons
74.62.Dh Effects of crystal defects, doping and substitution

Forces acting on a current-driven moving vortex in a long Josephson junction

D.-X. Chen, E. Pardo, and A. Sanchez

Appl. Phys. Lett. 90, 142512 (2007); http://dx.doi.org/10.1063/1.2720350 (3 pages) | Cited 2 times

Online Publication Date: 5 April 2007

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The current-driven vortex motion in a resistively shunted long Josephson junction is calculated. It is shown that the force on the vortex exerted by an ac Josephson current or a bias current routinely assumed for studying Josephson transmission lines is a Lorentz force, whereas the driving force on the vortex acted by a transport dc Josephson current is a London force, which could have an expression apparently similar to that of a Lorentz force with an opposite sign.
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74.50.+r Tunneling phenomena; Josephson effects
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Enhancement of Curie temperature under low electric fields in Mn selectively δ-doped GaAs/AlGaAs wide quantum wells

Bin Lv, Jiqing Wang, Jianguo Yu, Huibing Mao, Ye Shen, Ziqiang Zhu, and Huaizhong Xing

Appl. Phys. Lett. 90, 142513 (2007); http://dx.doi.org/10.1063/1.2720352 (3 pages) | Cited 4 times

Online Publication Date: 5 April 2007

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A prominent improvement of Curie temperature under low electric fields through Mn δ-doped GaAs/p-AlGaAs wide quantum wells is presented theoretically. The electric-field-controlled Curie temperature for different δ-doping positions and well widths has been investigated by means of the numerical self-consistent calculation. For quantum wells with 40 nm well width, an applied electric field of 0.3 meV/nm enhances TC up to five times than ones without the applied field. Our results indicate that wide quantum wells (>20 nm) have more advantage than narrow quantum wells in the electric-field-controlled low dimensional ferromagnetic systems.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.65.Fg Quantum wells
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetic and transport behaviors in Ge1−xMnxTe with high Mn composition

W. Q. Chen, K. L. Teo, S. T. Lim, M. B. A. Jalil, T. Liew, and T. C. Chong

Appl. Phys. Lett. 90, 142514 (2007); http://dx.doi.org/10.1063/1.2720353 (3 pages) | Cited 3 times

Online Publication Date: 5 April 2007

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The authors investigate the magnetic and transport behaviors of Ge1−xMnxTe thin films with high Mn composition (x = 0.98) grown by solid-source molecular-beam epitaxy. The temperature-dependent magnetization (M-T) gives a Curie paramagnetic temperature θp ∼ 120 K, in contrast to the Curie temperature of TC ∼ 95 K obtained from the Arrott plot and temperature-dependent resistivity measurement. The resistivity and M-T behaviors can be attributed to weak localization effect of disordering. The authors discussed the ferromagnetism in Ge0.02Mn0.98Te on the basis of the Ruderman-Kittel-Kasuya-Yoshida interaction and clustering effect.
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75.50.Pp Magnetic semiconductors
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Le Other inorganic semiconductors

Anisotropy compensation and magnetostriction in TbxNd1−xFe1.9 cubic Laves alloys

Y. G. Shi, S. L. Tang, Y. J. Huang, L. Y. Lv, and Y. W. Du

Appl. Phys. Lett. 90, 142515 (2007); http://dx.doi.org/10.1063/1.2721128 (3 pages) | Cited 14 times

Online Publication Date: 6 April 2007

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Polycrystalline TbxNd1−xFe1.9 (0 ⩽ x ⩽ 0.8) cubic Laves phase alloys with MgCu2-type structure were prepared by high-pressure synthesis and subsequent low-temperature annealing. The crystal structure, magnetic properties, and magnetostriction have been investigated. The change of easy magnetic direction from ⟨100⟩ to ⟨111⟩ with increasing x up to 0.1 is detected by Mössbauer spectra. In accordance with Mössbauer effect study, both magnetization and magnetostriction analyses show that TbxNd1−xFe1.9 is an anisotropy compensation system and the compensation point is close to x = 0.1. The present work may open an avenue in searching magnetostrictive materials with inexpensive Nd.
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75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.66.Dk Alloys
81.40.Gh Other heat and thermomechanical treatments

Relationship between flux pinning and microstructure in MgB2 thin films with columnar grains formed by molecular beam epitaxy

H. Yamamoto, A. Tsukamoto, K. Saitoh, M. Okada, and H. Kitaguchi

Appl. Phys. Lett. 90, 142516 (2007); http://dx.doi.org/10.1063/1.2720272 (3 pages) | Cited 12 times

Online Publication Date: 6 April 2007

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The relationship between flux pinning and microstructure in MgB2 thin films with columnar grains was investigated. Two kinds of as-grown MgB2 thin films were prepared with or without inclination of columnar grain growth with respect to the substrate plane by using molecular beam epitaxy. In a magnetic field, maximum Jc was obtained when the field angle matched the direction of columnar grain growth. The fabricated MgB2 thin films showed a high critical current density of Jc = 1.3×105 A/cm2 in 14 T at 4.2 K. The present results give a direct proof of flux pinning originating in columnar grain boundaries for MgB2 thin films.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
74.78.-w Superconducting films and low-dimensional structures
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
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