Browsing by Author "Chang, L. J."

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Current induced localized domain wall oscillators in NiFe/Cu/NiFe submicron wires
(2012-12-10)
Chang, L. J.
;
Lin, Pang
;
Lee, S. F.
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材料科學與工程學系
;
Department of Materials Science and Engineering
We experimentally demonstrate domain wall (DW) oscillators excited by in-plane ac current through permalloy based pseudo-spin valve wires, which contain one pair of artificial protrusions. By measuring the spin-transfer-torque induced resonance of a pinned antiparallel transverse DW, under transverse external fields, we show that the antiparallel transverse DW oscillates with a resonance frequency as high as 2.92 GHz, depending on the widths of protrusions. For DW oscillations induced by injection of dc currents, the observed peaks in dV/dI associated with the reversible change of magnetoresistance are attributed to the reversible motions of the DW. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770306]
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.
;
Yu, C.
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Huang, S. Y.
;
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]
Magnetic Interaction in Domain Wall Depinning at Square Notch and Antinotch Traps
(2011-10-01)
Chang, L. J.
;
Yao, Y. D.
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Lin, Pang
;
Lee, S. F.
;
材料科學與工程學系
In this paper, we report on domain wall (DW) pinning and depinning behavior using square notch and antinotch in NiFe nanowires. The presence of the DW in the samples was probed experimentally from focus magneto-optical Kerr effect (MOKE) measurement and anisotropic magnetoresistance (AMR). Pinning strengths as well as distribution of depinning field were measured. DW traps with antinotches were found to be more effective than notches, and the DW kept its structure during the depinning processes. Simulations of the magnetization orientation agreed with our results.
Vortex Induced by DC Current in a Circular Magnetic Spin Valve Nanopillar
(2012-04-01)
Chang, L. J.
;
Lin, Pang
;
Lee, Shang Fan
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材料科學與工程學系
;
Department of Materials Science and Engineering
We investigate the characteristic of vortex states induced by a dc current in trilayer circular magnetic nanopillars experimentally. Our samples are designed such that both the soft and hard layers can contain a magnetic vortex and the interlayer is thick enough such that only dipolar interaction is important. The relative chiralities between the two layers' vortex configurations as functions of external field and current are studied with various diameters. We also perform micromagnetic simulation on the magnetization reversals to compare with the magnetoresistance (MR) curves measured at low current and with current induced magnetization states. The current induced magnetization behaviors due to the spin transfer torque effect and the additional Oersted field are clearly identified on the resistance behavior.