Bing-Mau Chen

MAGNETIC FORCE MICROSCOPY STUDY OF DOMAIN WALLS ON A THIN COBALT FILM

Two types of 180° 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.

Functional Structures of AgOx Thin Film for Near-Field Recording

The optical processes of the AgOx thin film under various laser pumping pulses are studied using an optical pump-probe system. Detailed changes of the reflectance measurements clearly show the different transition process of the dissociation of the AgOx thin film. The structures of dots and rings of written spots are observed in these processes. Two possible models of the distribution of the dissociated silver are proposed.

Positive giant magnetoresistance in ferrimagnetic/Cu/ferrimagnetic films

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.

Inorganic Write Once Media

A write-once disk with AlSi alloy was proposed and studied. A jitter of 6.5% and a modulation of larger than 0.8 were obtained at a linear velocity of 8.4 m/s. Jitter is less than 5% in the blue laser system at a clock frequency of 66 MHz and a linear speed of 8.25 m/s for track pitch of 0.68 and 0.45 µm disk.

Magnetic domain pinning in patterned magneto-optical material

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.

The Creation of Nanometer Magnetic Domain Structure via Artificially Pinning Hole of Magneto-Optical Recording Material

A novel method for pinning the magnetic domain in artificially pinning hole has been developed for magneto-optical (MO) thin film material Dy/sub x/(FeCo)/sub 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.

Blue laser inorganic write-once media

With the advantages of low cost, portability and compliance with ROM disc, write once disk has become the most popular storage media for computer and audio/video application. In addition, write once media, like CD-R and DVD-/+ R, are used to store permanent or nonalterable information, such as financial data transitions, legal documentation, and medical data. Several write once recording materials, such as TeO[1], TeOPd[2] and Si/Cu [3] have been proposed to realize inorganic write once media. Moreover, we propose AlSi alloy [4] to be used for recording layer of write once media. It had good recording properties in DVD system although the reflectivity is too low to be used for DVD-R disk. In this paper, we report the further results in blue laser system, such as the static and dynamic characteristics of write once media.

High magnetization exchange-couple double-layer TbFeCo for magnetic flux reading optical recording

High magnetization (Mr) and enhanced coercivity magneto-optical (MO) recording media TbFeCo (TFC) were investigated for hybrid magnetic flux reading/optical recording due to their large magnetic flux. To increase the stability of high Mr TFC media, dual-layer disks composed of TM-rich readout layer with saturation magnetization (MS)=370 emu/cm/sup 3/ and RE-rich memory layer were fabricated. Coercivity and interface energy between double layers as a function of active layer thickness were examined. By simulating thermo-magnetic writing, the dual-layer media were shown to be applicable for optical writing/magnetic flux reading recording.

Pinning magnetic domain via patterning artificial lattice under amorphous magnetic layer

Abstract 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 photo- lithography, 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.

Magnetic Domain Pinning in Lithographically Patterned Amorphous Magnetic Layer

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 the unpatterned MO layer. Moreover, the coercivity in the larger pinning sites area is higher than in the smaller pinning sites area.