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12 Jan 2004

Volume 84, Issue 2, pp. 161-308

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Appl. Phys. Lett. 84, 161 (2004); http://dx.doi.org/10.1063/1.1639505 (3 pages)

Hatice Altug and Jelena Vučković
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Simultaneous inductive determination of grain and intergrain critical current densities of YBa2Cu3O7−x coated conductors

A. Palau, T. Puig, X. Obradors, E. Pardo, C. Navau, A. Sanchez, A. Usoskin, H. C. Freyhardt, L. Fernández, B. Holzapfel, and R. Feenstra

Appl. Phys. Lett. 84, 230 (2004); http://dx.doi.org/10.1063/1.1639940 (3 pages) | Cited 28 times

Online Publication Date: 7 January 2004

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An inductive methodology simultaneously enabling the determination of grain- and intergrain critical current densities of YBa2Cu3O7−x coated conductors is developed. This noninvasive method is based on the identification of a clear peak in the reverse branch of the magnetization loop at a positive magnetic field, as a signature of the electromagnetic granularity inherent to these materials. A quantitative evaluation of the return magnetic field at the grain boundaries allows us to understand the existence of this magnetization peak and quantify the grain critical current density. This methodology is envisaged to sort out granularity effects from vortex pinning effects on coated conductors. © 2004 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena
61.72.Mm Grain and twin boundaries
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

High thermal stability of magnetic tunnel junctions with oxide diffusion barrier layers

Yoshiyuki Fukumoto, Ken-ichi Shimura, Atsushi Kamijo, Shuichi Tahara, and Hiroaki Yoda

Appl. Phys. Lett. 84, 233 (2004); http://dx.doi.org/10.1063/1.1639128 (3 pages) | Cited 12 times

Online Publication Date: 7 January 2004

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We developed two types of magnetic tunnel junctions (MTJs) that showed high thermal stability. One is a PtMn exchange-biased spin-valve MTJ with a CoFe/Al-oxide (AlOx)/NiFe free layer and a CoFeTaOx/CoFe pinned layer, and the other is a pseudo-spin-valve (PSV) MTJ with a CoFe/AlOx/NiFe soft layer, where AlOx and CoFeTaOx act as barriers for Ni and Mn diffusion toward the tunnel barrier, respectively. After 390 °C-1H annealing, the PSV MTJs maintained 28% and the SV MTJs 39% of tunnel magnetoresistance. Transmission electron microscopy observation of the SV MTJs after 380 °C-1H annealing revealed that the migrated Mn atoms were trapped at the CoFeTaOx layer. © 2004 American Institute of Physics.
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75.47.Np Metals and alloys
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
75.50.Bb Fe and its alloys

Resistance changes similar to ballistic magnetoresistance in electrodeposited nanocontacts

Erik B. Svedberg, Jonathan J. Mallett, Hanania Ettedgui, Li Gan, P. J. Chen, Alexander J. Shapiro, Thomas P. Moffat, and William F. Egelhoff

Appl. Phys. Lett. 84, 236 (2004); http://dx.doi.org/10.1063/1.1639147 (3 pages) | Cited 9 times

Online Publication Date: 7 January 2004

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We have studied the behavior of electrodeposited Ni and Fe nanocontacts in magnetic fields and the changes in resistivity (ΔR) that occur. Metallic particles suspended in plating solution, created and collected from the electroplating bath of a nanocontact that later exhibited high values of ΔR/R, have been transferred to a second set of electrodes, in which similar high values of ΔR/R were measured without any plating process being performed. We attribute this effect to a mechanical reorientation of magnetic nanoparticles at the junction between the electrodes as the field is close to zero, and relate this work to present work with ballistic magnetoresistance in nanocontacts. We also show that Fe whiskers brought in close contact can produce this effect as well. © 2004 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
73.63.Rt Nanoscale contacts
75.47.Np Metals and alloys
81.15.Pq Electrodeposition, electroplating
82.45.Fk Electrodes

Electronic and magnetic properties of zinc blende half-metal superlattices

C. Y. Fong, M. C. Qian, J. E. Pask, L. H. Yang, and S. Dag

Appl. Phys. Lett. 84, 239 (2004); http://dx.doi.org/10.1063/1.1639934 (3 pages) | Cited 25 times

Online Publication Date: 7 January 2004

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Zinc blende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. We explore layered materials, consisting of alternating layers of zinc blende half-metals, by first principles calculations, and find that superlattices of (CrAs)1(MnAs)1 and (CrAs)2(MnAs)2 are half-metallic with magnetic moments of 7.0μB and 14.0μB per unit cell, respectively. We discuss the nature of the bonding and half-metallicity in these materials and, based on the understanding acquired, develop a simple expression for the magnetic moment in such materials. We explore the range of lattice constants over which half-metallicity is manifested, and suggest corresponding substrates for growth in thin film form. © 2004 American Institute of Physics.
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73.21.Ac Multilayers
75.30.Cr Saturation moments and magnetic susceptibilities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.66.Dk Alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.21.Cd Superlattices

Improving the ratio of the grain-boundary and bulk critical currents in YBa2Cu3O7−δ film

V. K. Vlasko-Vlasov, H. Claus, U. Welp, K. E. Gray, B. Ma, and U. Balachandran

Appl. Phys. Lett. 84, 242 (2004); http://dx.doi.org/10.1063/1.1639503 (3 pages) | Cited 2 times

Online Publication Date: 7 January 2004

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Magneto-optical images of flux patterns in a ring of epitaxial YBa2Cu3O7−δ film with an artificial 10° grain boundary are used to determine the ratio of the grain-boundary critical current to the bulk critical current. This ratio which first increases slowly with temperature is found to make a sharp upturn above 77 K showing that the grain-boundary critical current quickly converges to the bulk value at higher temperatures. From the measured ratio and the grain-boundary critical current obtained from magnetization, the temperature dependence of the bulk critical current is recovered. © 2004 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries

Ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields

I. M. Jiang, M. S. Tsai, C. K. Lu, C. C. Shih, J. C. Chiang, and H. E. Horng

Appl. Phys. Lett. 84, 245 (2004); http://dx.doi.org/10.1063/1.1639512 (3 pages) | Cited 7 times

Online Publication Date: 7 January 2004

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Applying an oscillating magnetic field perpendicularly on the high-quality magnetic fluid thin film, the phase separation of particles in the liquid matrix will occur. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. The ordered structure of magnetic fluid thin films is the basis for the potential optical application. We explore the dynamical ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields in this study. © 2004 American Institute of Physics.
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75.50.Mm Magnetic liquids
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
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