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18 Oct 2004

Volume 85, Issue 16, pp. 3343-3639

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3570 (2004); http://dx.doi.org/10.1063/1.1807953 (2 pages)

X. N. Zhang, C. R. Li, Z. Zhang, and Z. X. Cao
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Highly coercive electrodeposited FePt films by postannealing in hydrogen

K. Leistner, J. Thomas, H. Schlörb, M. Weisheit, L. Schultz, and S. Fähler

Appl. Phys. Lett. 85, 3498 (2004); http://dx.doi.org/10.1063/1.1807958 (3 pages) | Cited 26 times

Online Publication Date: 22 October 2004

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The properties of electrodeposited films subsequently annealed in H2 are reported and compared with those of vacuum-annealed samples. Annealing in hydrogen reduces the oxygen content incorporated during electrodeposition, resulting in significantly higher magnetization values. Phase formation is enhanced by hydrogen and L10 ordering starts at temperatures as low as 350°C. In addition, grain growth is hindered. These effects contribute to the high coercivity of 1.1 T achieved after annealing at 600°C in H2.
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75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
81.15.Pq Electrodeposition, electroplating

Spin-dependent boundary resistance in the lateral spin-valve structure

T. Kimura, J. Hamrle, Y. Otani, K. Tsukagoshi, and Y. Aoyagi

Appl. Phys. Lett. 85, 3501 (2004); http://dx.doi.org/10.1063/1.1805698 (3 pages) | Cited 39 times

Online Publication Date: 22 October 2004

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We report the detection of clear spin-valve signal without any spurious magnetoresistive signal in a lateral spin-valve structure consisting of Cu∕Ni−Fe ohmic junction using local current injection. The obtained spin-valve signal is much larger than that of the nonlocal spin-valve configuration because of the efficient spin accumulation. The local current injection experiments with different probe configurations proved that the spin-valve signal is caused by the spin-dependent boundary resistance at the interface between the ferromagnetic voltage probe and the spin-polarized nonmagnetic wire.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.25.Hg Electrical injection of spin polarized carriers
73.40.Cg Contact resistance, contact potential
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.50.Bb Fe and its alloys

Direct observation and analysis of nanoscale precipitates in (Sm,Eu,Gd)Ba2Cu3Oy

M. Muralidhar, N. Sakai, M. Jirsa, N. Koshizuka, and M. Murakami

Appl. Phys. Lett. 85, 3504 (2004); http://dx.doi.org/10.1063/1.1805709 (3 pages) | Cited 12 times

Online Publication Date: 22 October 2004

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We employed atomic-resolution high-angle annular dark-field scanning transmission electron microscope to characterize the chemical composition and nature of the nanoparticles dispersed in melt-processed (Sm0.33Eu0.33Gd0.33)Ba2Cu3Oy superconductor. We found two types of stable nanometer-scale particles, small LRE-Ba2CuZrOy and (LRE,Zr)BaCuOy (LRE=Sm,Eu,Gd) ones, in the 10–60 nm range, and larger particles of Gd2BaCuO5 “Gd-211,” around 100 nm in size. A substantial increase of critical current density was observed up to 90 K. Experimental data were interpreted in terms of additive pinning by “large” defects and a point-like disorder. The nanosized particles open a new horizon for production of bulk high-Tc superconducting magnets.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.37.Lp Transmission electron microscopy (TEM)

A model for asymmetric giant magnetoimpedance in field-annealed amorphous ribbons

N. A. Buznikov, CheolGi Kim, Chong-Oh Kim, and Seok-Soo Yoon

Appl. Phys. Lett. 85, 3507 (2004); http://dx.doi.org/10.1063/1.1806565 (3 pages) | Cited 10 times

Online Publication Date: 22 October 2004

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A phenomenological model for the asymmetric giant magnetoimpedance (GMI) in field-annealed amorphous ribbons is developed. The effect of a surface crystalline layer on the GMI response is described in terms of an effective bias field appearing due to a coupling between the crystalline layer and amorphous phase. It is shown that the presence of the bias field changes drastically the GMI profile. At low frequencies, the domain-walls motion leads to a steplike change in the GMI response. At high frequencies, the domain-walls motion is damped, and the GMI profile exhibits asymmetric two-peak behavior. The calculated dependences are shown to be in a qualitative agreement with results of experimental studies of the asymmetric GMI in field-annealed Co-based amorphous ribbons.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Cc Other ferromagnetic metals and alloys
75.47.De Giant magnetoresistance
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Dq Amorphous semiconductors, metals, and alloys
75.60.Ch Domain walls and domain structure
81.40.Gh Other heat and thermomechanical treatments
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.40.Mg Numerical simulation studies

Experimental study of the influence of edge roughness on magnetization switching in Permalloy nanostructures

M. T. Bryan, D. Atkinson, and R. P. Cowburn

Appl. Phys. Lett. 85, 3510 (2004); http://dx.doi.org/10.1063/1.1806566 (3 pages) | Cited 24 times

Online Publication Date: 22 October 2004

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Rectangular Permalloy nanostructures with different edge roughness, but the same average width, were fabricated by controlled variations in the exposure conditions of an electron-beam lithography process. The average widths that were studied ranged from 200 to 640 nm. Structures were characterized individually using magneto-optical Kerr effect single-structure nanomagnetometry and scanning electron microscopy on the same structure. Increased edge roughness caused increased coercivity, except for 200-nm-wide structures. Large edge roughness doubled the coercivity of wide (>600 nm) structures. The coercivity of nominally identical structures (same roughness amplitude) differed by up to 20 Oe, suggesting that the specific edge profile influences magnetic switching.
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75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.Bc Nanocrystalline materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
78.20.Ls Magneto-optical effects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.Nd Micro- and nanolithography

Effects of high-intensity ultrasound on Bi2Sr2CaCu2O8+x superconductor

Tanya Prozorov, Brett McCarty, Zhihua Cai, Ruslan Prozorov, and Kenneth S. Suslick

Appl. Phys. Lett. 85, 3513 (2004); http://dx.doi.org/10.1063/1.1808500 (3 pages) | Cited 8 times

Online Publication Date: 22 October 2004

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Slurries of powdered Bi2Sr2CaCu2O8+x (BSCCO-2212) superconductor in high-boiling alkanes were irradiated with intense ultrasound. Significant enhancements of magnetic irreversibility as well as transport critical current are reported. The effects are dependent on the concentration of the slurry and are optimal for 1.5 wt % slurry loading. Electron microscopy shows that ultrasonic treatment leads to a change in grain morphology and intergrain welding. The observed enhancement of superconducting properties is consistent with the limitations in critical currents in BSCCO superconductor being due to intergrain coupling rather than intragrain pinning strength.
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74.72.-h Cuprate superconductors
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.25.Sv Critical currents
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
74.62.Yb Other effects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
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