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26 Dec 2005

Volume 87, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 87, 263102 (2005); http://dx.doi.org/10.1063/1.2150278 (3 pages)

Z. Zhong, G. Katsaros, M. Stoffel, G. Costantini, K. Kern, O. G. Schmidt, N. Y. Jin-Phillipp, and G. Bauer
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Observation of injection and pinning of domain walls in magnetic nanowires using photoemission electron microscopy

Luc Thomas, Charles Rettner, Masamitsu Hayashi, Mahesh G. Samant, Stuart S. P. Parkin, Andrew Doran, and Andreas Scholl

Appl. Phys. Lett. 87, 262501 (2005); http://dx.doi.org/10.1063/1.2139842 (3 pages) | Cited 25 times

Online Publication Date: 19 December 2005

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Photoemission electron microscopy is used to explore the injection and pinning of magnetic domain walls in 250-nm-wide, 20-nm-thick Permalloy nanowires. Domain walls are injected from a micron-sized elliptical nucleation pad at one end of the nanowire. A vortex-like structure is readily nucleated in this pad at low magnetic fields (<15 Oe), whereas injection of a domain wall into the nanowire requires significantly larger fields ( ∼ 60 Oe). Domain walls are pinned in the nanowire at notches patterned along the wire’s edges. The domain walls are observed to have vortex-like structures with chiralities that vary in successive experiments.
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75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Voltage-controlled epitaxial strain in La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)O3-PbTiO3(001) films

C. Thiele, K. Dörr, S. Fähler, L. Schultz, D. C. Meyer, A. A. Levin, and P. Paufler

Appl. Phys. Lett. 87, 262502 (2005); http://dx.doi.org/10.1063/1.2150273 (3 pages) | Cited 49 times

Online Publication Date: 20 December 2005

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Epitaxially grown La0.7Sr0.3MnO3 thin films show resistance modulations induced by the inverse piezoeffect of the employed Pb(Mg1/3Nb2/3)O3-PbTiO3(001) (PMN-PT) substrates. The in-plane strain state of the films can continuously be tuned by application of a piezovoltage to PMN-PT. The lattice deformation of a PMN-PT(001) substrate was quantified by x-ray measurements under an electric field. Variation of in-plane lattice parameters by ∼ 0.06% reversibly changes the resistance of the manganite films by up to 9% at 300 K and shifts the magnetic Curie temperature. Films of different thicknesses from 50 to 290 nm, offering different as-grown strain states, have been studied.
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77.65.-j Piezoelectricity and electromechanical effects
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films

Temperature independence of the spin-injection efficiency of a MgO-based tunnel spin injector

G. Salis, R. Wang, X. Jiang, R. M. Shelby, S. S. P. Parkin, S. R. Bank, and J. S. Harris

Appl. Phys. Lett. 87, 262503 (2005); http://dx.doi.org/10.1063/1.2149369 (3 pages) | Cited 32 times

Online Publication Date: 20 December 2005

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The spin polarization of electrons injected into GaAs from a CoFe/MgO(100) tunnel spin injector is inferred from the circular polarization of light emitted from a GaAs-based quantum well (QW) detector. The circular polarization strongly depends on the spin and electron hole recombination lifetimes in the QW. Using time-resolved optical techniques, we show that these lifetimes are highly temperature dependent. A peak in the charge lifetime versus temperature is likely responsible for the previously observed dip in the electroluminescence polarization. Evidence for a temperature-independent spin injection efficiency of ∼ 70% from 10 K to room temperature is found.
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72.25.Dc Spin polarized transport in semiconductors
75.47.-m Magnetotransport phenomena; materials for magnetotransport
78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.-p Spectroscopy of solid state dynamics
75.50.Bb Fe and its alloys
75.47.Pq Other materials

Martensitic transformation and shape memory effect in a ferromagnetic shape memory alloy: Mn2NiGa

G. D. Liu, J. L. Chen, Z. H. Liu, X. F. Dai, G. H. Wu, B. Zhang, and X. X. Zhang

Appl. Phys. Lett. 87, 262504 (2005); http://dx.doi.org/10.1063/1.2158507 (3 pages) | Cited 38 times

Online Publication Date: 27 December 2005

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Heusler alloy Mn2NiGa has been developed by synthesizing a series of ferromagnetic shape memory alloys Mn25+xNi50−xGa25 (x = 0–25). Mn2NiGa exhibits a martensitic transformation around room temperature with a large thermal hysteresis up to 50 K and a lattice distortion as large as 21.3% and has a quite high Curie temperature of 588 K. The martensite shows a high-saturated field up to 2 T. The excellent two-way shape memory behavior with a strain of 1.7% was observed in the single crystal Mn2NiGa. The magnetic-field-controlled effect created a total strain up to 4.0% and changed the sign of the shape deformation effectively.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Fabrication, structure, magnetic properties of highly ordered cobalt disulfide nanowire arrays

G. H. Yue, P. X. Yan, J. Z. Liu, X. Y. Fan, and R. F. Zhuo

Appl. Phys. Lett. 87, 262505 (2005); http://dx.doi.org/10.1063/1.2158521 (3 pages) | Cited 14 times

Online Publication Date: 27 December 2005

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Highly ordered arrays of parallel CoS2 nanowires with a diameter of about 50 nm and a length up to about 50 μm were synthesized by two electrical fields in an anodized aluminum oxide film. In this letter, fabrication, structure, magnetic properties of highly ordered magnetic cobalt disulfide nanowires arrays were studied. Also, a growth mechanism has been speculated.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Onset of percolation and the temperature dependence of the persistent critical current in YBa2Cu3O7−δ films

J. Jung, K. H. Chow, M. Egilmez, and A. Welsh

Appl. Phys. Lett. 87, 262506 (2005); http://dx.doi.org/10.1063/1.2158522 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2005

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We investigated the effects of oxygen redistribution on the temperature dependence of the critical current Ic(T) in YBa2Cu3O7−δ thin films. In order to induce a very slow “motion” of oxygen in the sample, we performed careful annealing of the films in argon at 175 °C. A gradual transformation of Ic(T) into a Ginzburg–Landau-like dependence of the form Ic(T) = Ico(1−T/Tc)3/2 is observed, implying that the superconducting film is being transformed into a percolative (filamentary) state upon annealing.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.F- Transport properties
74.25.Sv Critical currents
74.20.De Phenomenological theories (two-fluid, Ginzburg-Landau, etc.)
81.40.Gh Other heat and thermomechanical treatments

Resistance steps and large magnetoresistive effect in La0.67Sr0.33MnO3 nanoconstriction array

H. J. Liu and C. K. Ong

Appl. Phys. Lett. 87, 262507 (2005); http://dx.doi.org/10.1063/1.2158525 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2005

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The transport properties of La0.67Sr0.33MnO3 (LSMO) nanoconstriction array under large applied current with current density in the order of 105 A/cm2 have been investigated. A series of resistance steps were observed at 78 K with applied current up to 1.0 mA. The critical current value at which resistance jump occurs varied with temperatures and the applied magnetic fields. The observation was attributed to the local heating induced phase transition at the section of nanoconstrictions where phase separation is dominant. A large low field magnetoresistive ratio of 52.2% was achieved at 78 K with the magnetic field up to 3000 Gauss when the biased current was set to 0.34 mA. This LSMO nanoconstriction array shows promise in the application of magnetic field sensors.
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75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetostatic interactions in mesoscopic Ni80Fe20 ring arrays

J. Wang, A. O. Adeyeye, and N. Singh

Appl. Phys. Lett. 87, 262508 (2005); http://dx.doi.org/10.1063/1.2158488 (3 pages) | Cited 23 times

Online Publication Date: 27 December 2005

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We investigate, directly using magnetic force microscopy, the effect of magnetostatic interactions in arrays of Ni80Fe20 mesoscopic rings. The rings were fabricated on silicon substrate using deep ultraviolet lithography at 248 nm exposure wavelength. We observed that the transitions from onion-to-vortex and vortex-to-reverse onion magnetic states are strongly dependent on the edge-to-edge-spacing of the rings due to dipolar magnetostatic interaction. For a closely packed ring array, the transition from onion to vortex state occurs at a much lower field due to collective magnetic switching as compared with widely spaced rings. The remanent magnetic state is found to be very sensitive to the orientation of the applied field due to shape anisotropy.
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75.50.Bb Fe and its alloys
75.60.-d Domain effects, magnetization curves, and hysteresis
68.37.Rt Magnetic force microscopy (MFM)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials

Electronic structure of calcium hexaborides

Byounghak Lee and Lin-Wang Wang

Appl. Phys. Lett. 87, 262509 (2005); http://dx.doi.org/10.1063/1.2150578 (3 pages) | Cited 11 times

Online Publication Date: 28 December 2005

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We present a theoretical study of crystal and electronic structures of CaB6 within a screened-exchange local density approximation (sX-LDA). Our ab initio total energy calculations show that CaB6 is a semiconductor with a gap of >1.2 eV, in agreement with recent experimental observations. We show a very sensitive band-gap dependence on the crystal internal parameter, which might partially explain the scatter of previous theoretical results. Our calculation demonstrates that it is essential to study this system simultaneously for both crystal structures and electronic properties, and that the sX-LDA provides an ideal method for this problem.
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75.50.Pp Magnetic semiconductors
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds
75.50.Dd Nonmetallic ferromagnetic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

Controlled introduction of flux pinning centers in YBa2Cu3O7−x films during pulsed-laser deposition

C. Varanasi, P. N. Barnes, J. Burke, J. Carpenter, and T. J. Haugan

Appl. Phys. Lett. 87, 262510 (2005); http://dx.doi.org/10.1063/1.2143112 (3 pages) | Cited 18 times

Online Publication Date: 29 December 2005

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To introduce controlled random inclusion of nanometer-sized nonsuperconducting particulates in YBa2Cu3O7−x films for flux pinning enhancement, a special pulsed-laser-ablation YBa2Cu3O7−x target with a Y2BaCuO5 sector was made and the films were deposited on LaAlO3 substrates. Initial results showed that the films consist of 10–20 nm-sized precipitates. In a 0.5 μm thick film, a transport critical current density (Jc)>3 MA/cm2 at 77 K in self-field was measured. Magnetization Jc at 77 and 65 K showed significant improvements in these films with fine precipitates as compared to regular YBa2Cu3O7−x films (>10 times increase at 9 T, 65 K).
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.15.Fg Pulsed laser ablation deposition
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena
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