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21 May 2007

Volume 90, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 90, 213501 (2007); http://dx.doi.org/10.1063/1.2742294 (3 pages)

Jong-Hyun Ahn, Hoon-Sik Kim, Etienne Menard, Keon Jae Lee, Zhengtao Zhu, Dae-Hyeong Kim, Ralph G. Nuzzo, John A. Rogers, Islamshah Amlani, Vadim Kushner, Shawn G. Thomas, and Terrisa Duenas
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Enhanced current flow through meandering grain boundaries in YBa2Cu3O7−δ films

Rafael B. Dinner, Kathryn A. Moler, M. R. Beasley, and D. Matthew Feldmann

Appl. Phys. Lett. 90, 212501 (2007); http://dx.doi.org/10.1063/1.2740610 (3 pages) | Cited 7 times

Online Publication Date: 21 May 2007

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In YBa2Cu3O7−δ (YBCO) coated conductors grown by metal organic deposition, in-plane meandering of grain boundaries (GBs) has been linked to higher critical current density. The authors investigate this link in individual GBs using transport measurements and scanning Hall probe microscopy with current reconstruction. They observe current-induced flux entry into a coated conductor, then model its behavior by imaging YBCO films with single, straight GBs tilted at various angles to the applied current. They find a strong dependence of critical current on angle, sufficient to explain the enhancement observed for meandering GBs.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.F- Transport properties

Aggregation-based growth and magnetic properties of inhomogeneous Cu-doped ZnO nanocrystals

Xuefeng Wang, J. B. Xu, W. Y. Cheung, Jin An, and Ning Ke

Appl. Phys. Lett. 90, 212502 (2007); http://dx.doi.org/10.1063/1.2741408 (3 pages) | Cited 36 times

Online Publication Date: 21 May 2007

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The authors report on the ferromagnetic ordering in 1.86 at. % Cu-doped ZnO nanocrystals synthesized by a solvothermal route. The distribution of Cu in ZnO lattice was inhomogeneous. In the Cu-poor cores, a spin-split acceptor impurity band model was proposed to explain the ferromagnetism. While in the Cu-rich surface layers, the shallow donorlike defects generated by imperfect oriented attachment could not only compensate a few holes but also readily occupy the Cu 3d states to destroy CuO4 tetrahedra, hence resulting in the short-range antiferromagnetic clusters. As a result, an interesting exchange biasing phenomenon took place at the ferromagnetic/antiferromagnetic interface.
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81.07.Bc Nanocrystalline materials
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
75.10.Lp Band and itinerant models

Fast reversible thermoelectrical switching in manganite thin films

Saulius Balevičius, Nerija Žurauskienė, Voitech Stankevič, Piotras Cimmperman, Skirmantas Keršulis, Antanas Česnys, Sonata Tolvaišienė, and Larry Lee Altgilbers

Appl. Phys. Lett. 90, 212503 (2007); http://dx.doi.org/10.1063/1.2741602 (3 pages) | Cited 4 times

Online Publication Date: 21 May 2007

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The authors report on fast reversible switching of epitaxial and polycrystalline La0.83Sr0.17MnO3 films from the ferromagnetic to the paramagnetic state induced by high power nanosecond electrical pulses. It was demonstrated that for the epitaxial films adiabatic and uniform Joule heating is the reason of the switching. For polycrystalline films, electronic processes reduce the film resistance within a subnanosecond. For longer times, adiabatic nonhomogeneous heating plays the main role in the switching dynamics. Possible device applications of this phenomenon are also discussed.
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73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Enhanced switching current density due to resonant precession in current-induced magnetization switching

Woojin Kim, Taek-Dong Lee, Jang-Eun Lee, Se-Chung Oh, Kyung-Ho Shin, Hong-Ju Suh, and Kyung-Jin Lee

Appl. Phys. Lett. 90, 212504 (2007); http://dx.doi.org/10.1063/1.2742282 (3 pages) | Cited 3 times

Online Publication Date: 22 May 2007

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Micromagnetic investigation was performed on the influence of neighboring cells in a conventional rectangular array to the switching current density (Jc) in the current-induced magnetization switching. We found that the Jc was increased regardless of the relative switching direction to the overall stray field. It is because the precession of the magnetization in the switching cell induces a resonant precession in neighboring cells through magnetostatic interaction. The resonant precession disturbs a fast reversal and results in the enhanced Jc for a fixed pulse width. The enhancement increases as the distance between the cells decreases. Here we proposed a zigzag array which significantly suppresses the enhancement of Jc due to the resonant precession.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
84.30.Sk Pulse and digital circuits
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Self-homodyne rf demodulator using a ferromagnetic nanowire

A. Yamaguchi, H. Miyajima, S. Kasai, and T. Ono

Appl. Phys. Lett. 90, 212505 (2007); http://dx.doi.org/10.1063/1.2742588 (3 pages) | Cited 7 times

Online Publication Date: 22 May 2007

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The radio frequency (rf) demodulator using a spin-torque diode effect in a single ferromagnetic nanowire is proposed. This is the first self-homodyne rf demodulator with ferromagnetic nanowire, and it can demodulate the amplitude modulation rf signal whose baseband frequency corresponds to the ferromagnetic resonance frequency of the wire.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Controlling the magnetic anisotropy of CoPt/AlN multilayer films

Y. Hodumi, J. Shi, and Y. Nakamura

Appl. Phys. Lett. 90, 212506 (2007); http://dx.doi.org/10.1063/1.2742793 (3 pages) | Cited 6 times

Online Publication Date: 23 May 2007

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The magnetic anisotropy of sputter-deposited CoPt/AlN multilayer films has been studied in contrast with the multilayer films consisting of magnetic and noble metals. It has been found that the as-deposited multilayer film shows enhanced in-plane magnetic anisotropy compared with CoPt alloy film of equivalent thickness. However, upon thermal annealing in a vacuum, the film undergoes a smooth transition of magnetic anisotropy from in-plane to perpendicular direction; moreover, the anisotropy field and coercivity can be controlled by controlling the annealing temperature. Structural characterization has revealed that the perpendicular magnetic anisotropy of the annealed CoPt/AlN multilayer films is mainly of magnetoelastic origin.
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75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Effect of electrode composition on the tunnel magnetoresistance of pseudo-spin-valve magnetic tunnel junction with a MgO tunnel barrier

Y. M. Lee, J. Hayakawa, S. Ikeda, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 90, 212507 (2007); http://dx.doi.org/10.1063/1.2742576 (3 pages) | Cited 102 times

Online Publication Date: 24 May 2007

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The authors investigate the effect of electrode composition on the tunnel magnetoresistance (TMR) ratio of (CoxFe100−x)80B20/MgO/(CoxFe100−x)80B20 pseudo-spin-valve magnetic tunnel junctions (MTJs). TMR ratio is found to strongly depend on the composition and thicknesses of CoFeB. High resolution transmission electron microscopy shows that the crystallization process of CoFeB during annealing depends on the composition and the thicknesses of the CoFeB film, resulting in different TMR ratios. A TMR ratio of 500% at room temperature and of 1010% at 5 K are observed in a MTJ having 4.3 nm and 4-nm-thick (Co25Fe75)80B20 electrodes with a 2.1-nm-thick MgO barrier annealed at 475 °C.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions

Nanocrystalline soft magnetic ribbons with high relative strain at fracture

T. M. Heil, K. J. Wahl, A. C. Lewis, J. D. Mattison, and M. A. Willard

Appl. Phys. Lett. 90, 212508 (2007); http://dx.doi.org/10.1063/1.2742598 (3 pages) | Cited 6 times

Online Publication Date: 24 May 2007

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Melt-spun nanocrystalline/amorphous composite ribbons (e.g., Finemet and Nanoperm) have excellent soft magnetic properties but are notoriously brittle after crystallization. In this letter, the authors present their findings of increased relative strain at fracture in Co-rich nanocomposite soft magnetic ribbons compared to conventional nanocomposite ribbons. Bending tests of the Co-rich ribbons show relative strain at fracture values more than twice as high as a Nanoperm ribbon. These Co-rich alloys have excellent soft magnetic properties with potential for high temperature applications. A (Co0.90Fe0.08Ni0.02)88Zr7B4Cu1 ribbon annealed at 823 K for 3600 s has a high saturation magnetization of 131 A m2/kg and a low coercivity of 8 A/m.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
68.35.Gy Mechanical properties; surface strains
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

All MgB2 tunnel junctions with Al2O3 or MgO tunnel barriers

Heejae Shim, K. S. Yoon, J. S. Moodera, and J. P. Hong

Appl. Phys. Lett. 90, 212509 (2007); http://dx.doi.org/10.1063/1.2742909 (3 pages) | Cited 5 times

Online Publication Date: 24 May 2007

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All MgB2 thin film tunnel junctions with Al2O3 or MgO tunnel barriers were fabricated in situ on Si substrates in a molecular beam epitaxy system and their tunneling characteristics were investigated. In the quasiparticle tunneling spectra of the junction with Al2O3 tunnel barrier, we observed both superconducting gaps of MgB2, while only a small gap was seen with MgO tunnel barrier. Using a microscopic structural analysis, we found that the difference in the spectra is due to the crystal orientation difference of the MgB2 films: the film grown on Al2O3 was polycrystalline whereas the film grown on MgO was c-axis oriented.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.25.Jb Electronic structure (photoemission, etc.)

Ab initio study of magnetic interaction of Fe doped ZnO with intrinsic vacancies

A. Debernardi and M. Fanciulli

Appl. Phys. Lett. 90, 212510 (2007); http://dx.doi.org/10.1063/1.2742597 (3 pages) | Cited 11 times

Online Publication Date: 25 May 2007

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The authors report on the calculation, by density functional theory, of the total energy and of the magnetic properties of wurtzite ZnO doped with diluted Fe impurities in the presence of vacancies. They found that the complex FeZn–VZn—where the Zn vacancy (VZn) occupies the next nearest neighbor position to Fe atom—is energetically favored compared with the isolated FeZn and VZn. An opposite situation was obtained for FeZn and VO. For Zn-poor growth condition, the room temperature population of the FeZn–VZn complex provides a key to understand the magnetism of this system.
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71.15.Nc Total energy and cohesive energy calculations
61.72.J- Point defects and defect clusters
75.30.Et Exchange and superexchange interactions
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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