Browsing by Author "Lee, SF"

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Current detection of vortex motion in patterned S-shape wires with constrictions
(2006-04-15)
Chen, YC
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Yao, YD
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Lee, SF
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Lin, YA
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Chen, DC
The current-driven effect on the vortex domain wall in a series-connected permalloy S-shape patterns was investigated. When a domain wall is initially formed in the wire section, in contrast to the ac result, applying a low dc current (J similar to 10(5) A/cm(2)) will break the degeneracy of the switching energy in different connected sections. Moreover, three kinds of effects on vortex states are observed by applying a high dc current (J similar to 10(7) A/cm(2)). The current applied slightly below the original switching field will drive vortices to constrictions while the current applied far below the original switching field will only perturb the vortex to another stable state. At the fields slightly over the original switching field, the domain walls are initially trapped at constrictions, injecting current will cause both the depinning and deformation of vortices. (C) 2006 American Institute of Physics.
Current-assisted magnetization switching in submicron permalloy S-shape wires with narrow junctions
(2005-05-15)
Chen, YC
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Lin, YA
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Chen, DC
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Yao, YD
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Lee, SF
We report the results of the current-assisted magnetization switching in submicron permalloy S-shape wires with narrow junctions (or notches). Domain walls were initially formed and pinned in the vicinity of the notches. Two distinct behaviors are observed in the current-assisted magnetization reversal process. When the applied field is near switching field (Delta H < 7 Oe), the injected current directly switched the wire magnetization, and the needed critical current varied linearly and significantly with the field intensity. In contrast, when the field is relatively far from the switching field (Delta H > 7 Oe), the current only moves the domain wall to a local stable state, and the critical current varied slightly with the field. Moreover, two resistance jumps during current scanning are observed in the cases with magnetization reversals. These results reveal that the current driven effect is closely related to the initial domain states, and are explained by a theoretical model based on spin transfer effect. (c) 2005 American Institute of Physics.
Magnetic switching and reversal process in a tip ring structure
(2004-06-01)
Liou, Y
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Chen, DC
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Yu, C
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Chen, JS
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Lee, SF
Patterned Permalloy submicron-size structures have been fabricated by e-beam lithography in the shape of a ring with a tip. A tip was intentionally added into the ring as a geometrical defect to interrupt the continuity of the magnetization, which aligns along the ring, in order to pin the domain wall. Magnetic switching and reversal process have been measured by the magnetoresistance measurement. The switching field about 260 Oe was obtained. At the remanent state, there was a 0.21% difference in the magnetoresistance between the angles of 90degrees and 0degrees that was equivalent to the domain wall magnetoresistance. By applying an external field, the domain wall moved along the ring under a lower field (100 Oe), which is smaller than the switching field. A drop (0.24%) in the resistance between the angle of 70degrees-120degrees has been observed that means the domain wall was moving into the voltage measuring region during the rotation. (C) 2004 American Institute of Physics.
Mn,Cd-metallothionein-2: A room temperature magnetic protean
(2006-02-24)
Chang, CC
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Lee, SF
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Sun, KW
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Ho, CC
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Chen, YT
Naturally occurring metallothionein (MT) is a metal binding protein, which binds to seven Zn2+ through 20 conserved cysteines and forms two metal binding clusters with a Zinc-Blende structure. We demonstrate that the MT, when substituting the Zn2+ ions by Mn2+ and Cd2+, exhibits magnetic hysteresis loop observable by SQUID from 10 to 330 K. The magnetic moment may have originated from the bridging effect of the sulfur atoms between the metal ions that leads to the alignment of the electron spins of the Mn2+ ions inside the clusters. The protein backbone may restrain the net spin moment of Mn2+ ions from thermal fluctuation. The modified magnetic-metallothionein is a novel approach to creating molecular magnets with operating temperatures up to 330 K. (c) 2005 Elsevier Inc. All rights reserved.
Perpendicular interface resistance in Co/NbxTi1-x multilayers for normal and superconducting NbTi alloy with x=0.4, 0.6
(2005-05-15)
Huang, SY
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Lee, SF
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Huang, JC
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Hwang, GH
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Yao, YD
We report here the resistance of Co/NbxTi1-x multilayers, for x=0.4 and 0.6, with current flowing perpendicular to the layer plane at 4.2 K. When NbTi films are sandwiched between Co, we found that there are critical thicknesses of 20 nm for x=0.4 and 27 nm for x=0.6, below which no superconducting transition could be found. Using a series resistor model, we extracted the unit area resistance of one pair of Co/NbTi interfaces and compared with the pure Nb case we have reported. The influence of mean free paths and superconducting coherence lengths is analyzed. (c) 2005 American Institute of Physics.
Temperature dependence of magnetic properties in Ni-Mn-Ga shape memory alloys
(2004)
Lee, MD
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Nong, NV
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Thuy, NP
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Yao, YD
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Lee, SF
Due to exhibiting giant field-induce strain, the Ni2MnGa shape memory alloys are great interest for both scientific researches and industry applications. The non-stoichiometric Ni50Mn25+xGa25-x alloys with x varied from 1.5, 2.5 to 4 have been fabricated by arc-melting. Martensitic transformation temperature for structure transformation from tetragonal to cubic (T-M) was observed from the magnetization, electrical resistivity and X-ray diffraction studies as functions of temperature below 400 K. We found that T-M increases roughly from 280 K to 310K with increasing x from 1.5 to 4. However, the Curie transition (T-M) is roughly at 380 K for all the samples, it is insensitive to the variation of Mn/Ga ratio. The electrical resistivity data exhibit a deep near T-M and a slope change near T-C. We have experimentally demonstrated that the shape memory effect can be occurred at room temperature with a proper concentration variation of Mn and Ga. (C) 2004 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.
Vortex domain wall depinning by polarized current in submicron half-ring wires
(2006-04-15)
Chen, YS
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Cheng, KW
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Yu, C
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Lee, SF
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Chen, DC
Domain wall pinning force in the junctions (corners), with different shapes of square, semicircle, or triangle, of half-ring in-series wires is considered to study the current injection induced wall movements. This geometry has less thermal activation at the region of domain wall nucleation in contrast to notch structures. The wires with square corners have the largest domain pinning force to resist polarized current-induced magnetization reversal, judging from the largest slope in the current-field dependence (Delta I/Delta H=0.274). (C) 2006 American Institute of Physics.