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3 Nov 2008

Volume 93, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 93, 181101 (2008); http://dx.doi.org/10.1063/1.3009599 (3 pages)

Nanfang Yu, Romain Blanchard, Jonathan Fan, Federico Capasso, Tadataka Edamura, Masamichi Yamanishi, and Hirofumi Kan
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Magnetic domains in magnetostrictive Fe–Ga alloys

Q. Xing and T. A. Lograsso

Appl. Phys. Lett. 93, 182501 (2008); http://dx.doi.org/10.1063/1.3013575 (3 pages) | Cited 16 times

Online Publication Date: 3 November 2008

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Lorentz microscopy was applied to the observation of magnetic domains in iron-gallium (Fe–Ga) alloys. Results did not show any link between the magnetic domains and the magnetostriction enhancement by Ga addition, but did reveal that the drastic decrease in magnetostriction for Fe–31.2 at. % Ga was due to the presence of large scale precipitates. Magnetic domain features did not change in the alloys of A2, D03, A2+D03, A2+B2+D03, and A2+fine scale precipitates. Large scale precipitates within the slow-cooled Fe–31.2 at. % Ga affected both the distribution and wall motion of magnetic domains.
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75.60.Ch Domain walls and domain structure
75.80.+q Magnetomechanical effects, magnetostriction

Series array of incommensurate superconducting quantum interference devices from YBa2Cu3O7−δ ion damage Josephson junctions

Shane A. Cybart, S. M. Wu, S. M. Anton, I. Siddiqi, John Clarke, and R. C. Dynes

Appl. Phys. Lett. 93, 182502 (2008); http://dx.doi.org/10.1063/1.3013579 (3 pages) | Cited 2 times

Online Publication Date: 3 November 2008

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We have fabricated a series array of 280 superconducting quantum interference devices (SQUIDs) using YBa2Cu3O7−δ thin film ion damage Josephson junctions. The SQUID loop areas were tapered exponentially so that the response of the current-biased array to magnetic field is a single voltage spike at zero field. We fitted the current-voltage characteristics of the array to a model in which we summed the voltages across the SQUIDs assuming a resistively shunted junction model with a normal distribution of SQUID critical currents. At 75 K the standard deviation of these critical currents was 12%.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors

The physical origin of open recoil loops in nanocrystalline permanent magnets

Bo Zheng, Hong-Wei Zhang, Su-fen Zhao, Jing-lan Chen, and Guang-heng Wu

Appl. Phys. Lett. 93, 182503 (2008); http://dx.doi.org/10.1063/1.3013837 (3 pages) | Cited 6 times

Online Publication Date: 3 November 2008

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The numerical simulation of the open recoil loops has been carried out using micromagnetic finite element method. By giving an example for this issue, the magnetization behaviors during the recoil processes of nanocomposite Pr2Fe14B/α-Fe magnets have been analyzed. It is the strong intergrain exchange coupling that results in the magnetization reversal in some hard grains during the recoil processes, which leads to the large opening of recoil loops. The magnetization reversal of α-Fe grain follows that of its neighboring hard grains. Consequently, the opening of recoil loops is enhanced due to the presence of α-Fe grains.
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75.40.Mg Numerical simulation studies
75.60.Jk Magnetization reversal mechanisms
75.50.Ww Permanent magnets
75.30.Et Exchange and superexchange interactions
75.50.Tt Fine-particle systems; nanocrystalline materials

Large tunnel magnetoresistance in Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunnel junctions prepared on thermally oxidized Si substrates with MgO buffer

Wenhong Wang, Hiroaki Sukegawa, Rong Shan, and Koichiro Inomata

Appl. Phys. Lett. 93, 182504 (2008); http://dx.doi.org/10.1063/1.3020300 (3 pages) | Cited 7 times

Online Publication Date: 4 November 2008

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Magnetic tunnel junctions (MTJs) using polycrystalline Co2FeAl0.5Si0.5 (CFAS) electrodes with a MgO tunnel barrier were fabricated onto thermally oxidized Si substrates. Highly (001)-oriented and B2-ordered CFAS electrodes were obtained by optimizing growth conditions and postannealing temperature. The microfabricated MTJs exhibited relatively high tunnel magnetoresistance (TMR) ratios of 125% at room temperature and 196% at 7 K. The large TMR obtained using oxidized Si substrates indicates that CFAS is promising for the practical applications.
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75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
82.45.-h Electrochemistry and electrophoresis

Dramatic strain induced modification of the low field anisotropic magnetoresistance in ultrathin manganite films

M. Egilmez, M. M. Saber, A. I. Mansour, Rongchao Ma, K. H. Chow, and J. Jung

Appl. Phys. Lett. 93, 182505 (2008); http://dx.doi.org/10.1063/1.3021083 (3 pages) | Cited 20 times

Online Publication Date: 6 November 2008

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The authors investigated the anisotropic magnetoresistance (AMR) in ultrathin La-based manganite films grown on various substrates. It was found that depending on the strain state, the AMR in some of these systems exceeds 100% and can even change sign. These changes are very dramatic when compared to the few percent change in AMR in conventional ferromagnets. The mechanism behind these large changes in the AMR is discussed.
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75.47.Lx Magnetic oxides
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

Magnetization logarithmic susceptibility, damping parameter, and dynamics symmetry extraction

Xiaobin Wang, Wenzhong Zhu, Haiwen Xi, Zheng Gao, and Dimitar Dimitrov

Appl. Phys. Lett. 93, 182506 (2008); http://dx.doi.org/10.1063/1.3021391 (3 pages) | Cited 1 time

Online Publication Date: 6 November 2008

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Magnetization logarithmic susceptibility is obtained for thermal assisted magnetization reversals under periodic driving forces. Using examples of magnetic elements excited by periodic spin torque currents, we demonstrate both theoretically and experimentally that frequency dependence of magnetization logarithmic susceptibility can be used to extract magnetization dynamics symmetry information and damping parameters for large amplitude nonlinear magnetization reversal.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Strain-induced change in local structure and its effect on the ferromagnetic properties of La0.5Sr0.5CoO3 thin films

C. K. Xie, J. I. Budnick, W. A. Hines, B. O. Wells, and J. C. Woicik

Appl. Phys. Lett. 93, 182507 (2008); http://dx.doi.org/10.1063/1.3011031 (3 pages) | Cited 12 times

Online Publication Date: 7 November 2008

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We have used high-resolution extended x-ray absorption fine-structure and diffraction techniques to measure the local structure of strained La0.5Sr0.5CoO3 films under compression and tension. The lattice mismatch strain in these compounds affects both the bond lengths and the bond angles, though the larger effect on the bandwidth is due to the bond-length changes. The popular double exchange model for ferromagnetism in these compounds provides a correct qualitative description of the changes in Curie temperature TC, but quantitatively underestimates the changes. A microscopic model for ferromagnetism that provides a much stronger dependence on the structural distortions is needed.
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78.70.Dm X-ray absorption spectra
75.30.Et Exchange and superexchange interactions
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Understanding eigenfrequency shifts observed in vortex gyrotropic motions in a magnetic nanodot driven by spin-polarized out-of-plane dc current

Youn-Seok Choi, Sang-Koog Kim, Ki-Suk Lee, and Young-Sang Yu

Appl. Phys. Lett. 93, 182508 (2008); http://dx.doi.org/10.1063/1.3012380 (3 pages) | Cited 13 times

Online Publication Date: 7 November 2008

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We observed sizable eigenfrequency shifts in spin-polarized dc-current-driven vortex gyrotropic motions in a soft magnetic nanodot, and clarified the underlying physics through micromagnetic numerical calculations. It was found that the vortex eigenfrequency is changed to higher (lower) values with increasing Oersted field (OH) strength associated with the out-of-plane dc current for the vortex chirality parallel (antiparallel) to the rotation sense of the OH circumferential in-plane orientation. The eigenfrequency shift was found to be linearly proportional to the current density j0 in the linear regime as in ΔνD ≃ ±ηj0/|G|, where G is the gyrovector constant and η is a positive constant, e.g., 1.9×10−8 erg/A for a model Permalloy dot of 300 nm diameter and 20 nm thickness. This behavior originates from the sizable contribution of the OH to the effective potential energy of a displaced vortex core in the gyrotropic motion. The present results reveal that νD, an intrinsic dynamic characteristic of a given nanodot vortex state, is controllable by changes in both the density and direction of spin-polarized out-of-plane dc currents.
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72.25.Ba Spin polarized transport in metals
75.50.Tt Fine-particle systems; nanocrystalline materials
73.63.Bd Nanocrystalline materials
75.40.Mg Numerical simulation studies

Size-dependent exchange bias in half-doped manganite nanoparticles

S. M. Zhou, L. Shi, H. P. Yang, Y. Wang, L. F. He, and J. Y. Zhao

Appl. Phys. Lett. 93, 182509 (2008); http://dx.doi.org/10.1063/1.3021370 (3 pages) | Cited 26 times

Online Publication Date: 7 November 2008

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Magnetic properties of the nanosized half-doped manganite of Sm0.5Ca0.5MnO3 with different particle sizes prepared by a sol-gel method are investigated. Exchange-bias phenomena are observed in the field-cooled magnetic hysteresis loops for these nanoparticles. The values of the exchange field, coercivity, remanence asymmetry, and remanent magnetization are found to depend strongly on the particle size. Particularly, as the particle size decreases, the exchange field shows a nonmonotonic variation with a maximum at ∼ 120 nm. These magnetic behaviors have been explained in terms of size effects on the charge ordered and antiferromagnetic manganite nanoparticles.
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75.30.Et Exchange and superexchange interactions
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ee Antiferromagnetics

Room temperature magnetoelectric control of micromagnetic structure in iron garnet films

A. S. Logginov, G. A. Meshkov, A. V. Nikolaev, E. P. Nikolaeva, A. P. Pyatakov, and A. K. Zvezdin

Appl. Phys. Lett. 93, 182510 (2008); http://dx.doi.org/10.1063/1.3013569 (3 pages) | Cited 24 times

Online Publication Date: 7 November 2008

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The effect of magnetic domain wall motion induced by electric field is observed in epitaxial iron garnet films grown on (210) and (110) gadolinium-gallium garnet substrates. The displacement of the domain wall changes to the opposite at the reversal of electric field polarity, and it is independent of the magnetic polarity of the domains. Dynamic observation of the domain wall motion in 400 V electric pulses gives the domain wall velocity of about 50 m/s. The same velocity is achieved in a magnetic field pulse of about 50 Oe. This type of magnetoelectric effect is implemented in single phase material at room temperature.
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75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Gg Ferrimagnetics
75.80.+q Magnetomechanical effects, magnetostriction
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
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