Browsing by Author "Chen, D. C."

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Demonstration of edge roughness effect on the magnetization reversal of spin valve submicron wires
(2010-07-12)
Chiang, T. W.
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Chang, L. J.
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Yu, C.
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Huang, S. Y.
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Chen, D. C.
We prepared submicron wide trilayer spin valve wires designed with periodic "spikes" as artificial roughness. The height and the pitch of the spikes were varied systematically. No obvious dependence was found between the roughness and the domain wall velocity when the spikes were smaller than a threshold of 30 nm for NiFe. The average velocity was slowed down when the height of the spikes were larger than the threshold. In-plane transverse magnetic fields help to reduce the critical current density for current induced domain-wall motion. Our results could be attributed to the space modulation of the local magnetization. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3463459]
Determining vortex chirality in ferromagnetic ring by lateral nonlocal spin valve
(2008-04-01)
Chen, D. C.
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Yao, Y. D.
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Wu, J. K.
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Yu, C.
;
Lee, S. F.
We demonstrate detecting chirality of vortex state in a magnetic ring by lateral nonlocal spin-valve (NLSV) measurement. A Permalloy (Py) ring, a Py narrow wire, and copper contacts were used as spin injector, detector, and the normal-metal diffusive channel, respectively. By comparing the anisotropic magnetoresistance loop of the individual ring with NLSV loop, the vortex chirality and the related switching field of the ring can be determined. Both onion-to-vortex transition field and vortex chirality were found to alternate in both the same and different current probe arrangements on the magnetic ring. (C) 2008 American Institute of Physics.
High-temperature magnetoresistance study of a magnetic tunnel junction
(2006-09-01)
Chen, D. C.
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Yao, Y. D.
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Chen, C. M.
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Hung, James
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Chen, Y. S.
The thermal stability and the spin transportation phenomenon at room temperature and 140 degrees C of a series of magnetic tunneling junctions with the structure of bottom electrode/PtMn/Pinned layer/ AlO(x)/CoFe/NiFe/top electrode have been investigated. The MR ratio decreases from 33.5% at room temperature to 29% at 140 degrees C. The MR ratio at room temperature increases roughly 0.8% after thermal treatment at temperatures above 60 degrees C. This is related to the thermal relaxation of the strains existing in the samples. (C) 2006 Elsevier B.V. All rights reserved.
Magnetoresistance study of patterned permalloy nanostructures
(2008-05-01)
Chen, D. C.
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Mei, J. K.
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Wang, Y.
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Yao, Y. D.
;
Wu, J. K.
We demonstrated the domain wall motion along the direction of the perimeter of a permalloy ring in the onion state. From the magnetoresistance (MR) measurement with a rotating ring at different constant fields, the critical field to form the onion state is near 200 Gauss and the lowest field that can still drag the domain wall is between 20 and 10 Gauss. The results also revealed a tendency for angle shifting and indicated that the lowest field component in the perimeter direction (the tangential component) was near 10 Gauss at an applied field of 20 Gauss.
Quantitative analysis of magnetization reversal in patterned strip wire by magnetic force microscopy
(2006-09-01)
Chen, D. C.
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Chiang, D. P.
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Yao, Y. D.
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材料科學與工程學系
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Department of Materials Science and Engineering
Magnetic force microscopy (MFM) was used to investigate the magnetization reversal process in a patterned strip wire of permalloy thin film. The magnitude of the phase-shift of tapping mode MFM changed with the varying interactive magnetic force between the magnetic tip and the sample. By analyzing the change in values of the phase-shift. the behaviors of magnetization reversal of different local regions in a patterned strip wire can be quantitatively analyzed. The intensity of the phase-shift in the wider end is stronger than that in the narrower one. In contrast, due to a strong anisotropic effect. the coercive force in the narrower end (9 Oe) is larger than that ill the wider one (8 Oe). Therefore, the H-c in the neck section could become strongly affected by the competition of the head-to-tail magnetic configurations in the two parts of the strip wire, and this results in a small H-c in the neck section. In addition, in a simple neck shape connection in a strip NiFe wire, a single domain configuration can be easily changed to a two single domain magnetic configuration. (C) 2006 Elsevier B.V. All rights reserved.