Browsing by Author "Chen, BM"

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Carrier-to-noise ratio improvement with pulsed-laser readout on magnetically induced superresolution by center aperture detection disks
(1999-09-01)
Chen, BM
;
Yang, BW
;
Hwang, WK
;
Shieh, TE
;
Shieh, HPD
Magnetically induced superresolution by center aperture detection (MSR-CAD) using pulsed and conventional de schemes were applied to magneto-optical disks to quantitatively evaluate readout performances. By simulation and experiments, it was found that carrier-to-noise ratio (CNR) in the pulsed-laser readout was about 2.5 dB higher than that in the de readout scheme at mark size of 0.45 mu m or shorter, Therefore, pulsed readout is feasible to improve CNR and recording density in MSR-CAD disks.
Geometric shape dependence of coercivity for patterned magnetic thin films
(2000-02-01)
Wu, TH
;
Wu, JC
;
Wu, CS
;
Chen, BM
;
Shieh, HPD
The micro-strips with patterned magnetic domains using electron beam lithography have been made to study the geometric shape dependence of coercivity. The size of the micro-strip is 10 mu m x 30 mu m with 0.5 mu m periods hole arrays pattern. Arrays with different types of geometry, such as square- circle-, and ellipse-shapes have been made. amorphous rear-earth transition-metal (RE-TM) thin films with magnetic perpendicular anisotropy were deposited on the microstrips. The extraordinary Hall effect has been employed to measure the hysteresis loop and the coercivity of the sample. We have found that for the same deposited material, the magnitude of coercivity for various shapes are dissimilar. For example, the coercivity of the ellipse-shaped hole arrays is much larger than the coercivity of the square-shaped hole arrays. In addition, we observed that the coercivity of the patterned sites was larger than the sites without patterns for RE-dominated compounds and the coercivity of the patterned sites was smaller than the sites without patterns for TM-dominated compounds. The magnetic moments canting between RE and TM subnetworks will be used to explain the observed phenomena. (C) 2000 Elsevier Science B.V. All rights reserved.
Magnetic domain pinning in lithographically patterned amorphous magnetic layer
(1999-03-01)
Wu, JC
;
Huang, YW
;
Chen, BM
;
Wu, TH
;
Shieh, HPD
Artificial pinning sites have been fabricated for the magnetic domain pinning in perpendicular anisotropy magneto-optical (MO) thin film media. The pinning sites were radial hole array made by patterning a layer of radial gold grid on the silicon nitride (SiN) coated silicon (Si) substrate using a standard electron beam lithography. Various magnetization and demagnetization procedures were performed to investigate the magnetic domain pinning behavior. A polar Kerr microscope was used in situ to monitor the magnetic wall motion and a magnetic force microscope was employed to scan the magnetic domain structures. Magnetic domains were found to be pinned inside the hole array and resembled to the geometric shape of the holes. The coercivity in the patterned MO layer is much higher than in thr unpatterned MO layer. Moreover, the coercivity in the larger pinning sites area is higher than in the smaller pinning sites area.
Magnetic domain pinning in patterned magneto-optical material
(1999-04-15)
Wu, TH
;
Wu, JC
;
Huang, YW
;
Chen, BM
;
Schieh, HPD
Pinning magnetic domains with defined shapes have been made for magneto-optical thin film material. The pinning array of holes on the substrate was fabricated using electron beam lithography. The domain pinning behaviors were studied by applying an external magnetic field perpendicular to the film plane and imaged by atomic force microscopy in their remanent state. Magnetic domains were found to be pinned inside the hole arrays and reproduced the shapes of the holes. The coercivity in the patterned region is larger than in the nonpatterned region. Moreover, the coercivity inside the hole sites is larger than the land sites. (C) 1999 American Institute of Physics. [S0021-8979(99)38708-9].
Magnetic domain pinning in patterned perpendicular magnetic anisotropy material
(1999-07-01)
Wu, TH
;
Wu, JC
;
Chen, BM
;
Shieh, HPD
;
光電工程學系
A method for pinning magnetic domains with prescribed shapes has been developed for the magneto-optical thin film material Dy(x)(FeCo)(1-x). The pinning array of holes on the substrate was fabricated using electron beam lithography. The thin film of Dy(x)(FeCo)(1-x) sandwiched between SiN layers was deposited onto a patterned polymethyl methacrylate layer. The pinned domains acquire the shape of the holes, while the sharpness of their boundaries depends on the size of the holes. The stability of the pinned domains is affected by the sample's magnetization. In our experiments, the minimum stable domain size pinned within the hole array was found to be around 50 nm in diameter. (C) 1999 Elsevier Science B.V. All rights reserved.
Magnetic force microscopy study of domain walls on a thin cobalt film
(1998-05-01)
Lin, HN
;
Chiou, YH
;
Chen, BM
;
Shieh, HPD
;
Chang, CR
Two types of 180 degrees domain walls on a 115 nm cobalt film are observed by magnetic force microscopy. The surface Neel wall on top of an asymmetric Bloch wall is found inhomogeneous. with the width estimated to be around 200 nm. The width of the rhomb-structured cross-tie wall, on the other hand, is approximately 400 nm. The coexistence of these two types of domain walls indicates that their wall energies are comparable at the film thickness. (C) 1998 American institute of Physics.
Magnetic properties and recording characteristics of high magnetization exchange-coupled double-layer TbFeCo for magnetic flux reading optical recording
(2001-07-01)
Chen, BM
;
Lai, CH
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
The magnetic properties and recording characteristics of exchange-coupled double-layer (ECDL) disks consisting of a transition metal-rich TbFeCo readout layer with high magnetization and a recording layer were studied for magnetic flux reading optical recording. The effective coercivity of ECDL with rare-earth (recording)/transition metal-rich (readout) films could be greatly enhanced from 1.7 to 7.6kOe through exchange coupling between two active layers. Moreover, ECDL disks possess a lower recording bias field (100 Oe) and a lower onset field (- 150 Oe) for thernioniagnetic writing. The enhanced effective coercivity was explained by the Kobayashi model, and the lower bias field and onset field of ECDL disks were analyzed by the modified nucleation field model. The ECDL disks with magnetization over 300 emu/cm(3), high stability and low recording bias field are potentially applicable for magnetic flux readout toward high density recording at a high writing rate.
Magnetoresistance anomaly in DyFeCo thin films
(2001-06-01)
Wu, JC
;
Wu, CS
;
Wu, TH
;
Chen, BM
;
Shieh, HPD
Microstructured rare-earth-transition-metal DyFeCo films have been investigated using magnetoresistance and extraordinary Hall-effect measurements. The Hall loops reveal variation of coercive fields depending on the linewidth and the composition of the films. The magnetoresistance curves, with changes up to as high as 1.3%, show positive/negative magnetoresistance peaks centered on the coercive fields depending on the linewidth of the films only. The variation of the coercivity can be attributed to the magnetic moment canting between the Dy and FeCo subcomponents and the existence of the diverged magnetization on the edges, and the anomalous magnetoresistance peaks observed are discussed with the existing theories. (C) 2001 American Institute of Physics.
Pinning magnetic domain via patterning artificial lattice under amorphous magnetic layer
(1999-03-01)
Wu, TH
;
Wu, JC
;
Chen, BM
;
Shieh, HPD
;
光電工程學系
A novel method for pinning magnetic domains on pre-formatted pinning sites has been developed for perpendicular magnetic anisotropy magneto-optical (MO) thin film media. The pinning sites were artificial lattices made by patterning a layer of gold grid on the substrate using electron beam lithography. Compared with the work proposed using photolithography, our method showed the ability of making smaller pinning domains. Moreover, compared with our previous work using the same electron beam lithography method and creating hole arrays on polymethyl methacrylate, this new method could stand higher film deposition temperatures and avoid the MO films rapid deterioration on a PMMA substrate. In order to investigate the domain pinning behavior we did several different procedures and observed their corresponding domain pinning layouts. Magnetic domains were found to be pinned inside the lattice and resembled the geometric shapes of the lattice. The pinned domains acquired the shape of the lattice. In this article, the star-shaped type of geometry of grid arrays is presented. (C) 1999 Elsevier Science B.V. All rights reserved.
Positive giant magnetoresistance in ferrimagnetic/Cu/ferrimagnetic films
(2001-06-01)
Lai, CH
;
Lin, CC
;
Chen, BM
;
Shieh, HPD
;
Chang, CR
Spin valves composed of ferrimagnetic/Cu/ferrimagnetic layers were fabricated with the magnetization perpendicular to the film planes. By changing the composition of ferrimagnetic layers, both negative and positive giant magnetoresistance (GMR) can be observed in ferrimagnetic spin valves. For samples consisting of both transition-metal (TM-) rich TbFeCo and GdFeCo, negative GMR values were obtained. Due to the high resistivity of amorphous ferrimagnetic films, the shunting effect of Cu led to relatively small MR ratio. The negative MR effect was 1% for 1.7 nm Cu. For spin valves consisting of rare-earth (RE-)rich TbFeCo and TM-rich GdFeCo, positive GMR values were observed. A thin layer of Co was inserted between RE-rich TbFeCo and Cu to manipulate the sign of GMR. (C) 2001 American Institute of Physics.
Relaxation of pinned domains in patterned magnetic thin films
(2000-02-01)
Wu, TH
;
Wu, JC
;
Huang, YW
;
Ye, LX
;
Chen, BM
We have shown in previous papers that the magnetic domains could be pinned inside the artificially patterned hole arrays under suitable geometry aspect ratio. Nevertheless, we have found that if we reverse the magnetization directions through domain wall motion, the confined domains expand from smaller territory into larger territory for some samples. In addition, the pinned domains maintained the same moment's orientation after the domain expansion. The possible reason for the pinned domains to retain the same moment's orientation maybe those pinning holes that act as high anisotropy defects. Thus, domain wall motion was around the high anisotropy sites and only peeled away the domain in the land area while the enclosed domain of the hole area maintained the same orientation. Moreover, the feasible reason for the expansion domains is the coercive force, which is perpendicular to the side-walls and pinning the domains inside the holes, are relaxed and thus causing the domains growth. This phenomenon is called the relaxation of pinning domains. (C) 2000 Elsevier Science B.V. All rights reserved.
Synchronous trigger detection for pulse laser readout on super resolution erasable optical disks
(2000-02-01)
Yin, GC
;
Chen, BM
;
Tai, CP
;
Shieh, HPD
;
光電工程學系
The laser pulse readout scheme is advantageous in reading thermal super resolution disks, but the light modulation on the RF signal confuses the detection channel. A synchronous trigger detection scheme, using the pulse laser trigger signal to pick up the desired signal, is proposed to suppress the adverse effects of the light modulation. A 5-dB increase of the signal on an magneto-optical super resolution center aperture detection disk by the synchronous detection system was demonstrated experimentally.
The creation of nanometer magnetic domain structure in artificially pinning hole of magneto-optical recording material
(1998-07-01)
Wu, TH
;
Wu, JC
;
Chen, BM
;
Shieh, HPD
;
光電工程學系
A novel method for pinning the magnetic domain in artificially pinning hole has been developed for magneto-optical (Mo) thin film material Dy-x(FeCo)(1-x). The artificially pinning holes were fabricated using electron-beam lithography. Hole arrays with square, star, and circle shapes had been made in this study. However, the nanometer scale magnetic domains could be formed inside the hole arrays if the pinning hole geometry was not well defined, and the pinning domain may induce media noise.