Observations of Domain Nucleation and Growth in Magneto-Optical Recording Media (original) (raw)
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Characterization of magneto-optical recording media in terms of domain boundary jaggedness
Journal of Applied Physics, 1991
Noise in magneto-optical recording devices can be classified as system-related noise and media noise. Media noise is rooted in the magnetic and magneto-optical properties of the recording media. To investigate media noise and its relation to microstructure and micromagnetics of thin films, the jaggedness of magnetic domain boundaries is characterized using static domain observations in which the fractal dimension D is measured for the domain boundaries. Samples of TbFeCo deposited under similar conditions, but with slightly different compositions, exhibited different amounts of jaggedness, and hence, slightly different values of D, i.e., 1.05s;Dg 1.20. Temperature dependent measurements performed on a TbFe sample showed increasing D with increasing temperature, l.l9<D< 1.28 for 300 K $T<360 K. Possible sources of jaggedness include structural/magnetic inhomogeneities as well as competition between domain-wall energy and demagnetization.
Characterization of Magneto-Optical Media and Systems
This dissertation is concerned with the characterization of both the magneto-optic (MO) media and optical system used in MO recording. Amorphous rare earth-transition metal (RE-TM) thin films give rise to magnetic domain walls that are not smooth, but possess varying degrees of jaggedness. A figure-of-merit for domain wall jaggedness could be used to rank films with respect to their suitability for use in MO recording, since domain wall jaggedness has been shown to increase readout noise. Using a specially-constructed static tester, the measured fractal dimension of MO domain walls provides this figure of merit. The basic theory of fractal structures, two measurement techniques, and data from MO samples is presented. At the system level, accurate focusing and tracking is required to reliably and repeatedly write and read data on the media, while track position and focus are maintained. Three focusing and tracking methods are analyzed using scalar diffraction theory, including the ef...
Magnetic Anisotropy and Coercivity in Magneto-Optical Recording Materials
Journal of the Magnetics Society of Japan, 1999
The perpendicular magnetic anisotropy of both amorphous Tb-Fe and crystalline fcc Pt-rich Co-Pt alloys is enhanced by increasing growth temperature, up to the onset of significant bulk atomic mobility (approximately one third of the melting temperature). High growth temperature also stabilizes these materials against subsequent annealing which tends to eliminate the anisotropy. The dependence on growth temperature can be fit with a two-level systems analysis in which the low energy surface state during growth is anisotropic. The source of this low energy state is suggested to be related to surface segregation for the Co-Pt alloys. The anisotropy for both materials shows very little dependence on substrate type, sample thickness, or details of the deposition such as sputtering or e-beam evaporation. Coercivity on the other hand is extremely dependent on microstructure and hence on details of preparation, substrate type, thickness, and crystallographic orientation. For a-Tb-Fe, the dominant mechanism appears to be domain wall pinning by microstructural defects in the bulk of the film, such as columnar microstructure.
Journal of Magnetism and Magnetic Materials, 1991
The reversible magnetisation relaxation has been investigated during remanent magnetisation and demagnetisation processes in various recording media and has been found to exhibit a maximum around remanent coercivity in particulate media. This can be explained in terms of particle switching and a computer model based on coherent rotation gives a good qualitative fit. The magnitude of the reversible effects during the various remanent processes are related and observed second order effects are discussed in the context of interactions. Longitudinal thin film media with different film structures have also been investigated and large differences in their reversible behaviour are described.
Thin Solid Films, 2003
The magnetization switching of CoNiO and CoCrPtTa thin films for longitudinal recording media on hard and flexible substrate, respectively, is studied by means of 3d magneto-optic Kerr effect vector magnetometry, which enables the determination of the evolution of the magnetization vector, in orientation and modulus, during the variation of the applied field. The analyzed CoNiO films have both a single-layered and a triple-layered structure. The presence of a multilayered structure partly modifies the magnetization reversal towards a larger degree of coherence. The rotation of the magnetization results highly incoherent in CoCrPtTa. The magnetization is observed to go partly out of the film plane during the switching, which indicates the presence of an out-of-plane anisotropy. The comparison of the obtained results points out a different degree of incoherency of the magnetization switching in the different thickness CoCrPtTa films, which can be related to their different microstructure. ᮊ
Present and future of magnetooptical recording materials and technology
Journal of Alloys and Compounds, 1998
Erasable optical information storage from amorphous rare earth-transition metal (RE-TM) alloys media has led to impressive improvements towards hyper high density recording in the past five years. Write / erase and readout processes are based on light-induced thermomagnetic switching of magnetic domains and magnetooptical (MO) Kerr effect, respectively, in ferrimagnetic films exhibiting a uniaxial magnetic anisotropy. The route towards ultrahigh optical areal densities was open from the beginning of the nineties from two key technologies related to near field optical techniques and RE-TM exchange-coupled bi, tri-and multilayers. The performances of the MO media depend on the types and states of these multilayers with perpendicular or mixed (perpendicular and planar) anisotropies which change with the temperature and the applied field. The development of the thermomagnetooptical materials is discussed with reference to their magnetic and MO properties to increase the density storage.
A SURVEY OF THE MAGNETIZATION REVERSAL FOR CoCr FILMS AND SOME PARTICULATE RECORDING MEDIA
Journal of the Magnetics Society of Japan, 1989
In addition to previous research on the magnetization reversal for sputtered CoCr films, two particulate perpendicular recording media, namely Ba-ferrite and Alumite have been measured. For comparison an isotropic Ba-ferrite sample and an in-plane ' "(Fe20s magnetic tape have also been evaluated. Only a few properties are compared which have been determined from the field-and angle-dependent VSM measurements. It was discovered for high HC.L/Hk CoCr films and the orientated Ba-ferrite media, in which
DOMAIN ANALYSIS AND MAGNETIC RELAXATION IN THIN FILMS
We have simulated the magnetic relaxation (M (t)) and the nucleation of magnetic domains in the presence of magnetic field in thin films with anisotropy perpendicular to the film plane. We have used Monte Carlo simulations based on the two-dimensional classical Ising model including the long-range dipole–dipole and Zeeman interactions. Domains nucleated during the magnetic relaxation exhibit very rough interfaces. We analyze the roughness and the M (t) as a function of the relative strength of dipole–dipole and Zeeman terms. Over the last decade magnetic thin films have attracted much attention, mainly due to technological applications. In particular, thin films with high perpendicular anisotropy appear to be a promising solution to increase the information density storage in magneto-optical recording (MO) media. The properties of magnetiza-tion processes in thin films, such as domain nucleation, time stability and domain interface roughness, are crucial points to be considered in the performance of MO storage. In such systems the high perpendicular anisotropy lock the magnetic moments so that they point up or down relative to the film plane and this symmetry suggests the use of the Ising Hamiltonian. In this paper, we will discuss the dynamics of nucleation processes in thin films with perpendicular anisotropy using Monte Carlo simulations. We are interested in discussing the magnetic relaxation and the morphology of magnetic domains such as shape and fractal dimensions. In our model, the spin interactions are described by a two-dimensional classical Ising Hamiltonian, including the long-range dipole–dipole interaction and an external magnetic field. Considering that time effects are hard to solve
Micromagnetics of Magnetization Reversal in Patterned Magnetic Recording Medium
IEEE Transactions on Magnetics, 2000
Selected aspects of the recording physics of data storage systems based on patterned magnetic recording medium are discussed. The micromagnetic study of the magnetization reversal in patterned magnetic recording medium is presented. The effects of bit size, head/medium misregistration, bit-to-bit spacing, soft underlayer (SUL) patterning, and side wall roughness on magnetization reversal are explored. The results offer the guidelines for the design and optimization of patterned magnetic recording medium.