Browsing by Author "Yao, YD"

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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
;
Lee, SF
;
Lin, YA
;
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
;
Lin, YA
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Chen, DC
;
Yao, YD
;
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.
Development of micromagnetic bearing motors with suppressed magnetic coupling effect for small form factor optical drives
(2006-04-15)
Wang, CC
;
Yao, YD
;
Wang, SJ
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材料科學與工程學系
;
Department of Materials Science and Engineering
The aim of this paper was to design a micromagnetic bearing (MMB) motor for small form factor optical drives. A MMB motor was developed with inner and outer magnetic-ring stack structure of high permeability. These rings were arranged on the shaft above the permanent magnet of the rotor and the stator. The magnetic force between the MMB, the permanent magnet, and the stator induced the magnetic coupling effect that generated the demon friction torque loss. However, the loss was controlled well under 1.93x10(-4) N m by the proposed approach, so that the good stable system was achieved. After suppressing the loss caused by the magnetic coupling effect, the shaft can be rotated without any frictional contacts in radial direction, the running current was around 0.18 A, and the maximum speed was around 1850 rpm. It shows that the MMB demonstrates the lower friction torque loss in comparison with the conventional microball bearing (MBB). Moreover, the radial vibration of our device is 21% lower than the conventional MBB type. To verify the performance of the provided system, both the computer simulation and the experiment were performed. (C) 2006 American Institute of Physics.
Effects of an Os layer on the magnetic properties of CoFe/IrMn
(2006-04-15)
Peng, TY
;
Lo, CK
;
Chen, SY
;
Yao, YD
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材料科學與工程學系
The uses of Os as an antidiffusion and buffer layer in IrMn exchange coupled CoFe film were investigated. For the purpose of antidiffusion, the inserted Os layer showed a distinct improvement of S>0.9, with H-C slightly increasing by 1.6 times for the CoFe/Os/MnOs multilayer after 400 degrees C annealing, even though the Os thickness was as thin as 0.3 nm. Furthermore, with a 0.3 nm Os barrier, the 350 degrees C annealed CoFe/Os/IrMn/CoFe showed almost the same magnetic behavior as the as-deposited state, while the H-ex of the upper part of the CoFe/Os/IrMn changed from 100 to 190 Oe. In addition, as a buffer layer, the Os buffer layer could enhance the diffraction peak intensities of IrMn(111)/Os(002) and CoFe (111), and the H-ex of CoFe/IrMn was proportional to the Os thickness. A 120 Oe of H-ex was achieved by using an 11 nm Os buffer layer in a CoFe 10 nm/IrMn 15 nm bottom type film. These results show that Os has the potential to be an antidiffusion and buffer layer in a magnetic multilayer. (C) 2006 American Institute of Physics.
Impedance behavior of spin-valve transistor
(2006-04-15)
Peng, TY
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Chen, SY
;
Hsieh, LC
;
Lo, CK
;
Huang, YW
The magnetoimpedance (MZ) effect of the pseudo-spin-valve transistor (PSVT) was investigated at room temperature in the frequency ranged from 100 Hz to 15 MHz. The PSVT can be regarded as a complex combination of resistors, inductors, and capacitors, while the impedance (Z) consists of a real part, the resistance (R), and an imaginary part, the reactance (X). Besides, all these components exhibit magnetic hysteresis. It is due to the frequency dependent behavior that R does not reach a minimum at the resonant frequency (f(r)). The frequency dependences of MZ and MX ratios cross zero at f(x)=6.5 MHz and at f(r)=3.65 MHz, respectively. The shape of magnetoreactance (MX) loop is reverse to the magnetoresistance (MR) loop; furthermore, MX ratio changes sign from negative at f < f(r) to positive at f>f(r). The MZ loop also reverses shape and sign after crossing f(x). For instance, the MZ loop with a ratio of 0.077% at 6 MHz switches to -0.086% and -0.125% at 7 and 8 MHz, respectively. (C) 2006 American Institute of Physics.
Magnetic force-induced damping effect for magnetic bearing motor
(2005-05-15)
Wang, CC
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Yao, YD
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Chang, YH
;
Tung, PC
;
Xiao, RB
An innovative damping induced by magnetic force was designed successfully for a totally passive magnetic bearing motor. A magnetic ring of high permeability and an annular-shaped rubber pad were mounted on the stator 0.55 mm below the permanent magnet of the rotor. Computer simulations were compared with experimental measurements to decide on the material and configuration of the critical components. The natural frequencies for lateral and rotational modes of the rotor are around 22 Hz measured by impulse method. Both the magnetic bearing motor with and without magnetic damping are rotated at a rated speed of 3840 rpm, which is far above the first critical speed of 1305 rpm. Without magnetic damping, the natural damping ratio in the radial direction of the rotor is 0.0655. After damping, it increases to 0.1401. We have demonstrated by both experimental measurement and theoretical calculation that the antishock performance is significantly improved by the innovative damping technology in a passive magnetic bearing motor. (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
;
Yu, C
;
Chen, JS
;
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.
Magnetoresistance behavior of Ni layer under Cu film
(1998-04-01)
Wu, CY
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Yao, YD
;
Lin, JJ
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物理研究所
;
Institute of Physics
The weak-localization effect is very sensitive to the presence of magnetic moments. We use it to study the formation of localized moments in thin Ni layers under a 100 Cu film. The Ni thickness varies between 0 and 4 Angstrom. We measured the magnetoresistance (MR) of these samples at temperatures ranging from 0.4 to 21 K. The magnetic field with the strength of up to 1 T, was applied normal to the film surface. We find that MR is more positive In samples with Ni underlayer than in Cu film. Comparing our results with the prediction of weak localization theory, the magnetic moment is detected only in Ni underlayers thicker than 2 Angstrom.
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.
Study of annealing and exchange bias effects in PtMn based magnetic tunnel junction system
(2004)
Peng, TY
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Yao, YD
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Chen, SY
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Wang, YH
;
Chen, WC
The crystallization structure and thickness of PtMn layer in a magnetic tunnel junction system are important factors to improve its exchange bias effect. This study shows that the PtMn layer could be changed from a FCC (111) structure to a FCT (111) structure after annealing above 270 degreesC. The minimum thickness of PtMn layer is found to be 10 nm for exchange coupling effect to be occurred in our MTJ system. The magnetic exchange effect between PtMn and SAF layers is near 4,300 Oe. Annealing temperatures can be higher than 400 degreesC for samples without patterning; however, temperature at 275 degreesC is too high for samples after patterning. This may be due to the breakdown of edges of the patterned samples as well as the complicated environments around the patterned samples. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Temperature dependence of magnetic properties in Ni-Mn-Ga shape memory alloys
(2004)
Lee, MD
;
Nong, NV
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Thuy, NP
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Yao, YD
;
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
;
Lee, SF
;
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.