Browsing by Author "Lee, S. F."

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Analysis of diffusive interface resistance for measurements with perpendicular current in Fe/Nb multilayers
(2006-04-15)
Huang, S. Y.
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Lee, S. F.
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Yu, C. Y.
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Hsu, S. Y.
;
Yao, Y. D.
In this study, we investigated the electron transport properties of interface between a ferromagnet and a superconductor with flowing current perpendicular to plan (CPP) at 4.2 K in Fe/Nb multilayers. The CPP resistance increased linearly with layer thickness and with bilayer number. We extracted the unit area resistance value of one pair of interface for superconducting and normal Fe/Nb by using a series resistor model. Hence, we can quantitatively analyze the interface resistance between Fe and Nb in the diffusive regime. (C) 2006 American Institute of Physics.
Analysis of the proximity effect and the interface transparency with perpendicular current in Ni/Nb system
(2009-04-01)
Huang, S. Y.
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Chiu, Y. C.
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Liang, J. J.
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Lin, L. K.
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Tsai, T. C.
We quantitatively study the interface resistance in Ni/Nb multilayers fabricated by sputtering system. For a fixed Ni layer thickness in Ni/Nb/Ni trilayers, the superconducting temperature T(c) decreases with decreasing Nb thickness. By analyzing the data with the proximity effect, the critical thickness below which superconductivity vanished was deduced. From current perpendicular to plane (CPP) measurement interpreted with a one-band series-resistor model, we obtained the CPP resistivities of Nb and Ni and the unit area resistances of 4.2 +/- 0.2 and 1.5 +/- 0.4 f Omega m(2) for superconducting and normal Ni/ Nb interfaces. The transparency parameter is directly calculated in terms of interface resistance. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073657]
Current induced localized domain wall oscillators in NiFe/Cu/NiFe submicron wires
(2012-12-10)
Chang, L. J.
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Lin, Pang
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Lee, S. F.
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材料科學與工程學系
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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.
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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.
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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.
Dimensional crossover and flux pinning of decoupled Cu(50)Ni(50)/Nb multilayers
(2008-04-01)
Huang, S. Y.
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Liang, J. -J.
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Tsai, T. C.
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Lin, L. K.
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Lin, M. S.
The behaviors of superconducting transition temperature T(c) and upper critical field H(c2) as a function of different superconductor thicknesses have been investigated in Cu(50)Ni(50)/Nb trilayers and multilayers. We deduced superconductor critical thickness, below which superconductivity vanishes, by analyzing the data in terms of proximity theory. The temperature dependence of H(c2) measurement reveals the spatial dimensional crossover and the flux pinning mechanism in the superconductor. A strong pair-breaking effect was observed in the weak ferromagnetic Cu(50)Ni(50) layers from both measurements. We attribute our observation to the high interface transparency between Cu(50)Ni(50) and Nb. (C) 2008 American Institute of Physics.
Interface resistance and transparency in ferromagnet/superconductor Co/NbxTi1-x multilayers (x = 1, 0.6, and 0.4)
(2007-07-01)
Huang, S.-Y.
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Lee, S. F.
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Hsu, S. Y.
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Yao, Y. D.
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電子物理學系
The quantitative interface resistance between polycrystalline ferromagnetic Co and NbxTi1-x, with x=1, 0.6, and 0.4, is measured and analyzed at 4.2 K. Both the superconducting and normal states of NbxTi1-x, respectively, above and below the superconducting critical thickness, are studied with current flowing perpendicular to the interface. A one-band series-resistance model is used to analyze our data. The interface transparencies in terms of the ratio between interface resistance and various physical quantities are discussed.
Investigation of Cu(0.5)Ni(0.5)/Nb interface transparency by using current-perpendicular-to-plane measurement
(2011-01-01)
Huang, S. Y.
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Liang, J. J.
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Hsu, S. Y.
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Lin, L. K.
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Tsai, T. C.
A direct determination of the interfacial transparency on the basis of current-perpendicular-to-plane (CPP) resistances for Cu(0.5)Ni(0.5)/Nb layered system is presented. This particular realization has substantial significance for understanding the interfacial transport in such heterostructures. The unexpected large critical thickness for this weak ferromagnetic containing system can be attributed to the strong pair-breaking effect as a result of the high interfacial transparency. Besides, the strong pair-breaking also plays a decisive role in the occurrence of the dimensionality crossover of the temperature dependent upper critical magnetic field.
Investigation of Cu0.5Ni0.5/Nb interface transparency by using current-perpendicular-to-plane measurement
(2011-01-01)
Huang, S. Y.
;
Liang, J. J.
;
Hsu, S. Y.
;
Lin, L. K.
;
Tsai, T. C.
A direct determination of the interfacial transparency on the basis of current-perpendicular-to-plane (CPP) resistances for Cu0.5Ni0.5/Nb layered system is presented. This particular realization has substantial significance for understanding the interfacial transport in such heterostructures. The unexpected large critical thickness for this weak ferromagnetic containing system can be attributed to the strong pair-breaking effect as a result of the high interfacial transparency. Besides, the strong pair-breaking also plays a decisive role in the occurrence of the dimensionality crossover of the temperature dependent upper critical magnetic field.
Magnetic Interaction in Domain Wall Depinning at Square Notch and Antinotch Traps
(2011-10-01)
Chang, L. J.
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Yao, Y. D.
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Lin, Pang
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Lee, S. F.
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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.
Properties of superconductivity for decoupled ferromagnet/superconductor trilayers and multilayers in Fe/Nb system
(2006-09-01)
Huang, S. Y.
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Lee, S. F.
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Liang, Jun-Jih
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Yu, C. Y.
;
You, K. L.
The transition temperature T(c) and upper critical field H(c2) of sputtered Fe/Nb trilayers and multilayers have been determined by measurement of electrical resistivity. For a fixed Fe layer thickness, T(c) decreases with decreasing Nb thickness up to a critical thickness d(Nb)(crit) approximate to 34 nm below which superconductivity vanishes. When the superconducting layers are thin (d(Nb) < 140 nm) and decoupled by pair breaking in the ferromagnetic layers, the parallel critical field exhibits nonlinear temperature dependence, revealing a change in the superconducting dimensionality. The strong decrease of T(c) with decreasing Nb thickness as well as the temperature dependence of H(c2) can be well described by theoretical model. (C) 2006 Elsevier B. V. All rights reserved.