Optical data recording with vanadium dioxide-based film reversible media

Thermally induced semiconductor-metal phase transitions taking place in Al/VO₂/insulator and VO₂/insulator film systems upon recording optical data are investigated. Experiments show that the rate of the processes depends on thermophysical parameters of the films, as well as on the energy exposure. The dynamic range of the energy exposure sensitivity is defined by the hysteresis loop width. The shape and width of the hysteresis loop depends on the VO₂ film thickness and the nonstoichiometric ratio profile across the film.     

Ultrahigh-density magneto-optical recording based on the effect of plasmon excitations

The analysis of ultrahigh-density recording in magneto-optical media formed with the use of granular CoAg(Au) films is performed. Due to excitation of plasma oscillations of electrons in granular CoAg(Au) films, the latter make it possible to perform additional focusing of recording radiation and to significantly decrease the size of memory cells. It is suggested that two-layer film CoAg(Au)/TbFeCo/substrate systems be used as recording media for magneto-optical recording. It is shown theoretically that the angle of the Kerr rotation of the plane of polarization θ_K upon magnetization of such a two-layer structure increases significantly in the range of incident-photon energy from 2 to 4 eV in comparison with the case of TbFeCo magnetic film. Some specific features were detected experimentally in the spectra of θ_K in the region of excitation of plasma oscillations in nanogranular CoAu and CoAg films at ? ω _P ≈ 2.5 and 3.5 eV, respectively, as well as in two-layer CoAg(Au)/TbFeCo film systems.     

Micro magnetic structure of magnetic clusters in CoCrTaPtB recording media

Micro magnetic structure in CoCrTaPtB recording media with H_c>3 kOe was studied by magnetic force microscope and LLG simulation. Two types of the characteristic magnetic structure were observed. One is the convergent-type magnetic structure, which is observed as localized magnetic cluster on bit. The other is the vortex structure, which is responsible for the recording bit peroration. These micro magnetic structures cause the medium noise in high-density recording and must be suppressed by adjusting coercive force H_c and inter-granular interaction to explore high density recording media.     

Optical recording using hydrogen phthalocyanine thin films

Vacuum sublimed thin films of the blue dye hydrogen phthalocyanine (H₂Pc) were incorporated into various optical recording structures. The dye was shown to be thermally, hydrolytically, and oxidatively stable. In all cases, the writing mechanisms are dependent on the sublimation of H₂Pc. Several recording structures which take advantage of the sublimation property of H₂Pc are demonstrated, including pit forming and bubble forming media. These H₂Pc-based optical recording structures show very high optical contrast and low writing threshold energies. In addition, very thin films (50–75Å) of H₂Pc were incorporated into a tellurium-based medium, which significantly enhanced the writing contrast observed in that medium.     

Preparation and recording characteristics of granular-type perpendicular magnetic recording media with thin intermediate layer

Granular-type media with thin Ru intermediate layer were prepared on a highly oriented high-B_s FeCo soft underlayer (SUL). A CoPt–TiO₂ recording layer on a Ru intermediate layer of only 2 nm had high-crystal orientation, high H_c of 6.5 kOe, and a high squareness ratio (SQ) of 0.99. The magnetic property of the SUL was also good. The recording performance was measured for the media with different Ru intermediate thicknesses by using a single-pole-type (SPT) head. The media had large reproduced output even for the Ru intermediate layer thickness of 2 nm.     

A novel analysis method for noise of perpendicular recording media

An in-field magnetic force microscopy (MFM) observation technology was introduced to study media noise in perpendicular recording medium. Magnetization reversal field (H_R) distribution of the recording medium could be mapped by this technology. We have extracted media noise signal image from recording pattern. The noise signal image was converted to a contour image, in which peak areas represented high-noise areas. To clarify the relationship between H_R distribution and the media noise, we novelly combined the contour with the H_R-map. The results show that the media noise mostly gets generated in the lower-H_R areas, which indicates the lower-H_R area is one of the important origins of the media noise. For comparison, a simulation work was also performed by introducing a model based on experimental parameters. The simulation agreed with experimental results very well.     

Advanced granular-type perpendicular recording media

We introduce our recent experimental results for three blocked layers for currently used perpendicular recording media; a recording layer (RL: for recording), a soft magnetic underlayer (SUL: magnetic flux path in writing), and a nonmagnetic intermediate layer (NMIL: underlayer of RL and separation layer between RL and SUL). For the NMIL, uniaxial crystallographic symmetry is an essential requirement for suppression of variant growth of magnetic grains in granular-type RL. From this view point, AlN with wurtzite structure and materials with pseudo-hcp structure, which means fcc structure with stacking faults, were found to be effective. For the SUL, disordered hcp CoIr with negative K_u were found to well suppress both spike noise and track erasure due to a wide distribution of magnetic flux under the return yoke in writing and formation of a Neel wall instead of a Bloch wall in the SUL. For the RL, positive-/negative-K_u stacked media with incoherent switching mode was found to be effective in order to solve the recent write-ability problem for high K_u RL material with high thermal stability. Applying all these items, an advanced medium concept with the stacking structure of “CoPtCr-oxide/CoIr-oxide/CoIr/pseudo-hcp nonmagnetic layer/substrate” is very promising from the view point of (1) switching field reduction of a RL with high K_u material, (2) conventional amorphous SUL free, and (3) conventional NMIL free.     

Two-center holographic recording in highly doped LiNbO3 crystals

In this paper, we report the observation of electron tunneling during two-center recording in LiNbO₃:Fe:Mn doped with high Fe concentration. Unlike tunneling in the singly doped lithium niobate that erases the hologram, the effect in two-center recording can improve the diffraction efficiency of the hologram after the recording while it is kept in the dark. A detailed study of this effect in LiNbO₃:Fe:Mn is presented both theoretically and experimentally. We show that the hologram strength may increase or decrease due to tunneling, depending on the experimental condition of recording. PACS 42.40.-i; 42.70.Ln; 42.40.Lx     

Novel approaches to high-density perpendicular recording media

Two different approaches to reduce the intermediate layer (IL) thickness in perpendicular recording media are proposed. Such a reduction in IL thickness could lead to improvement in writability and recording performance. The first approach involved the introduction of a magnetic intermediate layer (MIL), to obtain C-axis growth. Media with CoCr alloy layer as the MIL were studied. Reasonably good C-axis growth with a Δθ₅₀ of about 3.8° could be obtained for MIL thickness of about 10 nm. Noise could be controlled by introducing exchange-breaking layers. The other approach involved the use of crystalline soft underlayers (SUL) to obtain suitable growth conditions for the recording layers. For this purpose, CoFeTaCr alloys with a FCC(1 1 1) texture were prepared. A good C-axis dispersion in the recording layer with a Δθ₅₀ of about 3.1° could be obtained for IL thickness of about 5 nm. The present study indicates that the recording medium deposited on crystalline SUL is relatively noisier than that deposited on amorphous SUL. Reducing the noise of the crystalline SUL is a way towards higher areal densities.     

Direct near infrared photorefractive recording and pre-exposure controlled hole–electron competition with enhanced recording in undoped Bi12TiO20

We report the direct recording of electron-based photorefractive hologram in nominally undoped Bi₁₂TiO₂₀ crystals using 780 nm wavelength light without pre-exposure or any kind of previous processing. A lower intensity absorption grating is also detected. Pre-exposure with shorter wavelength produces an extended lifetime hole-based complementary grating on another photoactive center level and leads to enhanced recording.PACS 42.70.Nq; 42.70.Ln; 42.70.Gi; 42.65.Hw     

Effect of light polarization on holographic recording in glassy azocompounds and chalcogenides

Light polarization effects on a holographic grating recording in a glassy chalcogenide a-As₄₀S₁₅Se₄₅ film has been experimentally studied and compared with previously studied glassy molecular azobenzene film 8a at 633, using s − s,p − p, CE-1 and CE-2 circular-elliptic recording-beam polarizations (differing by light electric field rotation directions). The azocompound exhibited much higher self-diffraction efficiency (SDE) and diffraction efficiency whereas chalcogenide was more sensitive. Their recording efficiency polarization dependences also were different. SDE up to 45% was achieved in 8a with p − p and up to 2.6% in a-As₄₀S₁₅Se₄₅ with CE-2 polarized recording beams. The polarization changes in the diffraction process were studied as well in these and other materials (11, 16, 19 and a-As₂S₃ film, LiTaO₃:Fe crystal). It was found that light polarization changes in the process of diffraction from gratings recorded vectorially by s−p polarizations depended on chemical composition, wavelength, and exposure time. Vector gratings with SDE up to 25% were recorded in 8a, rotating a linear polarization by 90°. No light polarization changes were found in azobenzene 19 and chalcogenide films and in LiTaO₃:Fe crystal, thus showing a vector recording of scalar holograms. The recording mechanisms in azocompounds and chalcogenides are discussed and compared.     

Grain size reduction and recording performance improvement by using NiW as a partial interlayer in CoCrPt/SiO2 recording medium

We report the effect of NiW, as an interlayer to partially replace Ru, on the microstructure, magnetic properties, and recording performance of CoCrPt/SiO₂ perpendicular recording media. It was found that the full width at half maximum of the rocking curves of the Co (0002) peak changed little with NiW thickness up to 10 nm. However, further increase of NiW thickness caused a larger c-axis dispersion. The grain size of the CoCrPt/SiO₂ recording layer was reduced from 10.9±1.8 nm for the films without NiW to 7.7±1.5 nm for films with 10-nm NiW as a partial interlayer. The coercivity, H _c, nucleation field, H _n, and the reverse overwrite, Rev_OV, of the CoCrPt/SiO₂ layer did not change much (less than 15%) with increased NiW thickness. However, it did affect the switching field distribution of the CoCrPt/SiO₂ layer (more than double). The recording performance was improved by using NiW as a partial interlayer, which was mainly attributed to the reduced grain size.     

Study of near-infrared nonvolatile two-center holographic recording in LiNbO3:Fe:Rh crystal

The near-infrared nonvolatile holographic recording has been realized in a doubly doped LiNbO₃:Fe:Rh crystal by the traditional two-center holographic recording scheme, for the first time. The recording performance of this crystal has been investigated by recording with 633 nm red light, 752 nm red light and 799 nm near-infrared light and sensitizing with 405 nm purple light. The experimental results show that, co-doped with Fe and Rh, the near-infrared absorption and the photovoltaic coefficient of shallow trap Fe are enhanced in this LiNbO₃:Fe:Rh crystal, compared with other doubly doped LiNbO₃ crystals such as LiNbO₃:Fe:Mn. It is also found that the sensitizing light intensity affects the near-infrared recording sensitivity in a different way than two-center holographic recording with shorter wavelength, and the origin of experimental results is analyzed.     

Laser-induced optical recording in thin films

A model is presented to describe the hole opening in ablative optical recording. The model accounts for changes in geometry of the sensitive film, for adhesion of the film to the substrate, for surface tension gradients in the sensitive film and for evaporation or sublimation at the film-substrate interface. The changes in geometry during hole opening are shown to be responsible for an energy barrierF _act=10^?16 to 10^?15 J, corresponding to 1.5–6J/cm³ which is much too large to make thermal activation of hole opening possible.F _act is reduced by surface tension gradients in the liquid film and/or evaporation at the filmsubstrate interface. The predictions of the model are compared with laser recording experiments performed with Te-alloy films on various polymer sublayers. Experiments and model show that the threshold energyE _th for hole opening (andF _act) can be reduced by (i) lowering the surface tension and/or polarity of the polymer sublayer, (ii) reducing the dynamic work of adhesion, e.g. by decreasing the crosslink density or the mean molecular weight of the sublayer, and (iii) increasing the concentration of low molecular weight material in the sublayer, which reduces the adhesion of the film and stimulates evaporation at the interface.     

Study of the ambient optical recording dynamics on sputtered indium oxide thin films

2 O₃) thin films, grown by dc magnetron sputtering, using ultraviolet laser radiation at 325 nm, is investigated. Simultaneous measurements of the recording efficiency and electrical conductivity changes, under ambient conditions, prove that there is a strong relation between the two actions, and measurements of the recording efficiency with respect to the film conductivity history and temperature provide evidence for the presence of two coexisting processes in the recording regime. The reported results provide essential information on the mechanism and nature of holographic recording in this material. Received: 4 November 1997/Accepted: 16 November 1997     

Monocrystalline high-saturation magnetization ferrites for video recording head application: I. Zn ferrous ferrites

Monocrystalline Zn ferrous ferrites Zn_xFe_3-xO₄, with x ? 0.4, are considered as candidate materials for video recording heads, to be used for writing on magnetic tapes of high coercivity. The saturation magnetization of these ferrites can be as high as 0.7 T at 20°C. We show that because of the small dimensions of modern video recording heads, the relatively high electrical conductivity of the Zn ferrous ferrites is not an obstacle to their use at video frequencies. Measurements are reported of magnetic and electrical parameters relevant to recording head application. It is shown that some of the magnetic parameters can be influenced positively by Co^II additions. The present paper is the first of a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Evanescent wave holographic recording in nanosize thick chalcogenide glass films

The results of holographic gratings recording in 29, 15 and 8 nm thick As₂S₃ films are presented in the paper. The method is based on the interference of surface-propagating evanescent waves, created by total internal reflection. The condition for successful recording is the penetration depth of these inhomogeneous waves to be greater than the films thickness. In this case, the film’s refractive index does not affect the total internal reflection (TIR) condition and could be greater than the input glass prism. The experimentally obtained low diffraction efficiencies by this holographic recording technique is due to the very low refractive index modulation, but the good signal-to-noise ratio - better than 50:1 and Bragg-type diffraction are a base for future applications of this grating formation method in nanotechnology.     

Magnetic pigments for recording media

CrO₂ doped with 1--2 wt% Fe³⁺ on Cr⁴⁺ positions is one of the most important materials for magnetic recording in audio, data and video tapes. ⁵⁷Fe Mössbauer spectroscopy was applied to determine the level of iron doping in newly developed high coercivity CrO₂ particles. It was found that, compared with the conventional preparation process, the new particles contain increased amounts of Fe³⁺ ions in the CrO₂ crystal lattice giving rise to higher magnetocrystalline anisotropy. This is reflected in coercivities of up to over 900 Oe. All samples contain as a secondary iron-containing phase α-(Cr_1-xFe_x)₂O₃, the amount of which is higher in samples of the conventional preparation process than in those of the new BASF process. Details about the mechanism of the development of doped CrO₂ particles in both types of processes were obtained by means of Mössbauer, XRD and wet chemical investigations making possible an optimization of the new BASF process.     

Research and development of metal powder for magnetic recording

Since its first application within the compact cassette in 1978, magnetic recording media using metal powder have been improved at a rate of roughly 1 dB per year as a result of advances in such fields as tape materials, tape-making technologies, etc. Today, metal tapes have a widely expanded application area, including video and data-information applications. Dowa Mining Co., Ltd., began its research regarding magnetic powder for recording media in 1978. The Company successfully developed metal powder for 8 mm video tape. Since then, Dowa has endeavored to improve the magnetic properties and reduce the particle size of metal powder. It accomplishes these goals through the full use of the Company's unique Al doping method. Especially, during the past several years, significant improvements of the magnetic properties of metal powder have been achieved. These improvements have resulted from the introduction of new technologies, including Fe–Co alloying, sintering prevention, new reaction processes, and many other new techniques. Currently, Dowa Mining is supplying a new type of metal powder for the most technologically advanced high-density recording media. Dowa's new metal powder has an axis length of 0.1 μm, H_c of 2400 Oe, and σ_s of 155 emu/g.     

Theoretical consideration of pits recording and etching processes in chalcogenide vitreous semiconductors

We propose theoretical consideration, computer modeling and comparison with our recent experimental results for information pits recording and etching processes in chalcogenide vitreous semiconductors using Gaussian laser beam and selective etching. Our calculations demonstrate that photo-transformed region cross-section could be almost trapezoidal or parabolic depending on the photoresist material optical absorption, exposure, etchant selectivity and etching time. Thus our approach open possibilities how to select the necessary recording procedure and etching conditions in order to obtain pits with the optimum shape and sizes in As₄₀S₆₀ chalcogenide semiconductor. Obtained results quantitatively describe the characteristics of pits recorded by the Gaussian laser beam in thin film of As₄₀S₆₀.