Thermomagnetic Recording Research Articles

Thermomagnetic recording of highly Bi-substituted iron garnet film using scanning laser for spatial light modulation

Spatial light modulations (SLM) utilizing the magneto-optical (MO) effect of magnetic materials are expected to offer fast switching and small pixel sizes as small as the wavelength of the light. However, the small MO effect is a major issue. In this paper, we report a thermomagnetic recording of highly bismuth-substituted garnet film, known for large Faraday effects. Y0.5Bi2.5Fe4GaO12 (Bi,Ga:YIG) film with a Faraday rotation of −4.66 degrees was used as an MO medium. A laser scanning thermomagnetic recording system using a Galvanometer mirror was developed and the size and quality of recorded magnetic domains were investigated. The smallest recorded magnetic domain diameter was 0.62 μm with a small standard deviation of 0.09 μm. Line patterns with a width of 1 μm can be recorded in this film. We found that Bi,Ga:YIG films have potential as a material for SLMs with fast switching, submicron pixel size, and large MO effect.

Chasing Tails: Insights From Micromagnetic Modeling for Thermomagnetic Recording in Non‐Uniform Magnetic Structures

AbstractPaleointensities are key to understanding the formation and evolution of Earth and are determined from rocks which record magnetic fields upon cooling; however, experimental protocols for estimating paleointensities frequently fail. The primary reason is that laboratory protocols assume that rocks are dominated by uniformly magnetized, single‐domain grains, instead of much more common non‐uniformly magnetized grains. Our model for larger grains shows a multiplicity of stable domain states; with preferred states changing as a function of temperature. We show that domain state distribution depends on the thermal history of the sample—in nature and the laboratory. From numerical thermomagnetic modeling, we show that particles with non‐uniform domain states will theoretically fail standard experimental paleointensity protocols, preventing us from determining reliable ancient geomagnetic field intensities. We propose that recognizing this type of behavior, and the resulting bias, will yield more reliable paleointensity records, and a better understanding of the Earth.

Chasing tails: Insights from micromagnetic modeling for thermomagnetic recording in non-uniform magnetic structures - grain geometry file.

Chasing tails: Insights from micromagnetic modeling for thermomagnetic recording in non-uniform magnetic structures - grain geometry file.

Light-induced thermomagnetic recording of thin-film magnet CoFeB on silicon waveguide for on-chip magneto-optical memory.

Thermomagnetic recording is a technique used as a writing process for magneto-optical (MO) drives. Despite their significant advantages, such as rewritability, nonvolatility, reliability, and large cycling endurance, MO drives are rarely used today because of the complex drive systems that must deal with magnetic field and lightwave simultaneously. This study reports on the light-induced thermomagnetic recording of a ferromagnetic thin-film CoFeB on a Si photonic platform. Lightwave guided in the Si waveguide evanescently coupled to the thin-film magnet and underwent optical absorption, resulting in heating and a decrease in coercive force. Therefore, we observed magnetization reversal with an applied magnetic field for both continuous and modulated light pulses using a magneto-optical Kerr effect microscope, and the light-induced thermomagnetic recording was experimentally demonstrated on a Si photonic platform. The proposed scheme enables the realization of on-chip MO memories on the Si photonic platform in which neither bulky free-space optics nor mechanical rotation systems are required.

Magnetic Holography and Its Application to Data Storage

The principle of magnetic holograms and its application to holographic memory are reviewed. A magnetic hologram was recorded through a thermomagnetic recording as a difference in magnetization direction and reconstructed with the magneto-optical effect. To achieve a bright reconstruction image, it is important to record deep magnetic fringes on the materials with large Faraday rotation coefficients. This technique was applied to the holographic memory using transparent magnetic garnets as a recording material. The first reconstruction image was dark and noisy, but improvements in the recording conditions resulted in error-free recording and reconstruction of the magnetic hologram. To form deep magnetic fringes, insertion of heat dissipation (HD) layers into recording layer was proposed. It was found that this HD multilayer medium showed diffraction efficiency higher than that of a single layer medium, and error-free recording and reconstruction were also achieved, using magnetic assisted recording. These results suggest that HD multilayer media have potential applications in recording media of magnetic holographic data storage. In future, a high recording density technique, such as multiple recording, should be developed.

Development of heat dissipation multilayer media for magnetic hologram memory

AbstractHolographic memory is a strong candidate for next‐generation optical storage with high recording densities and data transfer rates, and magnetic hologram memory using a magnetic garnet, as the recording material, is expected to be used as a rewritable and stable storage technology. We succeeded in recording and reconstruction of two‐dimensional data in magnetic hologram without error. However, the diffraction efficiency is insufficiently high for actual storage devices. To increase the diffraction efficiency, it is important to record deep magnetic fringes, whereas the merging of fringes due to the excess heat near the medium surface generated during the thermomagnetic recording process must be suppressed. To avoid this merge of fringes, we proposed a multilayered structure in which the magnetic layers are divided by the transparent heat dissipation layers (HDL) to control the heat diffusion. In this study, we propose a simple thermal design method for designing the HDL multilayer structure. Using this model, we designed and fabricated an HDL multilayer medium in which the recording magnetic layers are discrete in the film. The HDL multilayer medium exhibited diffraction efficiency higher than that of the single‐layer medium, and error‐free recording and reconstruction were achieved using the magnetic assist technique.

Development of Heat Dissipation Multilayered Media for Magnetic Hologram Memory

Holographic memory is a strong candidate for next-generation optical storage with high recording densities and data transfer rates, and magnetic hologram memory using a magnetic garnet, as the recording material, is expected to be used as a rewritable and stable storage technology. We succeeded in recording and reconstruction of 2D data in magnetic hologram without error. However, the diffraction efficiency is insufficiently high for actual storage devices. To increase the diffraction efficiency, it is important to record deep magnetic fringes whereas the merging of fringes due to the excess heat near the medium surface generated during the thermomagnetic recording process must be suppressed. To avoid this merge of fringes, we proposed a multi-layered structure in which the magnetic layers are divided by the transparent heat dissipation layers (HDL) to control the heat diffusion. In this study, we propose a simple thermal design method for designing the HDL multilayer structure. Using this model, we designed and fabricated a HDL multilayer medium in which the recording magnetic layers are discrete in the film. The HDL multilayer medium exhibited diffraction efficiency higher than that of the single layer medium, and error-free recording and reconstruction were achieved using the magnetic assist technique.

Magnetic-force microscopy of thin Bi:IG films for thermomagnetic recording

Thermomagnetic recording on thin films is currently one of the most promising methods for copying records with high density and weak magnetization. These films can be characterized by a couple of parameters very suitable for recording reconfigurable magnetic atomic traps whose geometry is visible. Different types of materials are investigated to be the most effective for thermomagnetic recording propose. In this paper authors showed possibility and features of thermomagnetic recording on Bi:IG thin films. High coercivity thin films with low Curie temperature and different film-lattice mismatch parameters were synthesized. Thermomagnetic recording of magnetic disc was performed. Features of magnetic records were investigated and influence of film-lattice mismatch parameters on meta-stable domain structure that defines the thermomagnetic recording resolution was showed. Magnetic-force microscopy was used for topography and magnetic structure characterization of thin films with different film-lattice mismatch parameters. Some features of films morphology were investigated using atomic-force microscopy with sharp AFM probe.

Bi-Substituted Iron Garnet Films for Thermomagnetic Recording, Photonics, and Plasmonics: Optimization of Synthesis Conditions Using Scanning Probe Microscopy

We present the results of studies on the optimization of the synthesis of Bi-substituted iron garnet (Bi : IG) films by liquid-phase epitaxy and vacuum deposition followed by crystallization. The effect of the parameter of mismatch between the crystal lattices of the film and the substrate on the functional properties of thin single-crystal high-coercive Bi : IG films is demonstrated. The regime of high-temperature annealing of deposited films was optimized in order to form layers with a high bismuth concentration for magnetophotonic and magnetoplasmonic structures. It was established that annealing of the Bi : IG layer under a SiO2 layer deposited on top will reduce the roughness of interfaces in multilayer structures.

Influence of nanoholes array geometrical parameters on magnetic properties of Dy–Fe antidot thin films

Nanoscale artificially engineered spintronic materials could be used to enlarge the storage density of magnetic recording media. For this purpose, magnetic nanostructures such as antidot arrays exhibiting high uniaxial magnetic anisotropy are new contestants in the field of ultrahigh density magnetic data storage devices. In this context, we focus on the synthesis of nanostructured magnetic materials consisting of Dy–Fe alloyed antidot thin films, deposited onto the surface of nanoporous alumina membranes served as patterned templates. Noticeable variations of in the in-plane magnetic anisotropy have been observed by modifying the layer thickness at both microscopic and macroscopic scales. The microscopic magnetic properties have been locally studied by Nano-MOKE magnetometry. For thinner antidot samples with 15, 20 and 25 nm in thickness, a tri-axial in-plane magnetic anisotropy has been detected. Meanwhile, for thicker antidot samples (40–60 nm of layer thickness), an in-plane uniaxial magnetic anisotropy has been noted. We attribute these changes in the magnetic anisotropy to the strong correlation between the edge-to-edge distance among adjacent nanoholes, W, and the local magnetic anisotropy of antidot samples. The effective magnetic anisotropy exhibits an unexpected crossover from the in-plane to out-of-plane direction due to the increasing of the effective perpendicular magnetic anisotropy with varying the layer thickness of antidot thin films. Therefore, we detected a critical layer thickness, t = 25 nm for the Dy–Fe alloy antidot arrays, at which the appearance of the perpendicular magnetization is observed. Furthermore, an enhancement in the Curie temperature of the antidot arrays compared to the continuous thin films has been obtained. We attribute these effects to the complex magnetization reversal processes and the high thermal stability of the hexagonal structure of antidot arrays. These findings can be of high interest for the development of novel magnetic sensors and for thermo-magnetic recording patterned media based on template-assisted deposition techniques.

Development of Heat Dissipation Multilayer Media for Volumetric Magnetic Hologram Memory

Holographic memory is a strong candidate for next-generation optical storage, featuring high recording densities and data transfer rates, and magnetic hologram memory using a magnetic garnet, as the recording material is expected to be used as a rewritable and stable storage technology. However, the diffraction efficiency of magnetic holography depending on the Faraday rotation angle is insufficiently high for actual storage devices. To increase the diffraction efficiency, it is important to record deep magnetic fringes, whereas it is necessary to suppress the merging of fringes owing to heat diffusion near the medium surface. In this work, we investigated the recording process of magnetic holograms in detail with experiments and numerical simulations, and developed a multilayer media with transparent heat dissipation layers to record deep and clear magnetic holograms by controlling the heat diffusion generated during the thermomagnetic recording process. To suppress lateral heat diffusion near the medium surface, we designed and fabricated a multilayer magnetic medium in which the recording magnetic layers are discrete in a film, approximately 12-µm thick. This medium exhibited diffraction efficiency higher than that of the single-layer medium, and error-free recording and reconstruction were achieved using the magnetic assist technique.

Morphology of garnet films for thermo-magnetic recording

The work deals with the investigation of sensitivity of epitaxial garnet films for thermo-magnetic recording. The spatial resolution of replicas of inhomogeneous fields was associated with the morphological features of the films. Surface morphology of the intense epitaxial films was studied by optical methods and atomic force microscopy. It was shown that the changes in the block structure with an increase in the mismatch between the film-substrate constants occur.

Scanning probe microscopy of high-coercive iron garnet films

Mono-crystalline uniaxial anisotropy high-coercive garnet films are used for thermo-magnetic recording by laser beams or contact printing. High-coercive properties of garnet films are due to a significant mismatch between the lattice parameters of the film and the substrate. The mismatch leads to appearance of facet crystal structure in these films. In the work, the facet crystal and domain structures of high-coercive garnet films were established by methods of scanning probe microscopy.

High-coercive garnet films for thermo-magnetic recording

The possibility of using high-coercive of garnet films for thermo-magnetic recording is related with the presence of the metastable domain structure, which arises due to a significant mismatch of the lattice parameters of the film and the substrate. In the work the connection between facet crystal structure of elastically strained ferrite garnets films and the domain structure in them is established by methods of phase contrast and polarization microscopy.

Compensation behavior of a ferrimagnetic nanoparticle system with binary alloy shell

Abstract The phase diagrams and the magnetic properties of a spherical ferrimagnetic nanoparticle, consisting of a ferromagnetic core of atoms A with spin-1/2 ( S A = 1 / 2 ) surrounded by a disordered ferrimagnetic binary alloy shell of two kinds of atoms (A and B) with different spins ( S A = 1 / 2 and S B = 3 / 2 ) are studied by using Monte Carlo simulation based on the Metropolis algorithm. Depending on the values of the Hamiltonian parameters, the system presents a number of outstanding phenomena, such as the possibility of one, two or even three compensation point(s). The existence of a compensation temperature is an interesting phenomenon with important technological applications in the field of thermomagnetic recording.

Thermomagnetic writing into magnetophotonic microcavities controlling thermal diffusion for volumetric magnetic holography.

Holographic memory is expected to become a high-capacity data storage. Magnetic volumetric holograms are rewritable holograms that are recorded as magnetization directions through thermomagnetic recording. However, the effective depth of magnetic holograms is limited by thermal diffusion that causes merging of magnetic fringes. In this study, we propose the insertion of heat-sink layers (HSLs) for retaining well-defined magnetic fringes during volumetric writing. Magnetophotonic microcavity media were used for demonstrating the HSL effect, and the structural design principle was established in numerical calculations. The results indicate that deep and clear magnetic fringes and an improvement in the diffraction efficiency can be achieved by the insertion of HSLs.

Switching time in laser pulse heat-assisted magnetic recording using L1-FePt nanoparticles

Atomistic spin model simulations using Langevin dynamics are performed to study the factors that determine the thermomagnetic recording time window in FePt media. The onset of thermomagnetic writing occurs at a temperature To larger than the Curie temperature Tc as a result of the finite time of relaxation of the magnetization by the linear reversal mode. The Bloch relaxation rate of magnetization growth during cooling below Tc is independent on the write field, provided the field is stronger than some threshold value. Application of a strong write field reduces switching time through better spin alignment in the paramagnetic regime. Finite size effects on the probability distribution of freezing temperatures Tf and the free energy provide insight on the thermomagnetic reversal mechanism. Constraints on the “pulse-mode” of recording when the head field reverses direction during cooling are also considered.

Some methods of inducing high–coercivity state in epitaxial magnetic garnet films for thermomagnetic recording

Results of studying coercive force, optical absorption and lattice mismatch in single−crystal epitaxial magnetic garnet films are presented. It is shown that the reason of high values of both coercivity and optical absorption are the oxygen vacancies compensating Ca2+ ions and lattice mismatch stress. Methods of inducing high−coercivity state in Bi−containing garnet films through doping by bivalent impurity ions, through mismatch stress or through treatment in negative corona discharge are proposed. Merits and demerits of these methods are discussed and their comparison is carried out.

Colorization of Magnetic Hologram Images With Optical Space Division Method

We have developed magneto-optic spatial light modulators (MOSLMs) with submicrometer-size magnetic pixels for wide-viewing-angle holographic displays (3-D-MOSLM) that are driven by the thermomagnetic recording. The holographic images were reconstructed by the magnetic hologram pattern on the MOSLM. In this paper, we have studied colorization of reconstruction images of the MOSLMs using optical space division method. This method used some 3-D-MOSLMs to represent intermediate colors. The magnetic films were polycrystalline bismuth, dysprosium, and aluminum substituted yttrium iron garnet (BiDyYFeAlG) films with perpendicular magnetization. The thickness of BiDyYFeAlG films was designed for each wavelength. The MOSLM represented (3-D) images with intermediate colors that were synthesized 3-D images with red and green colors. In addition, tones of intermediate colors were represented by controlling intensity of each reference light. These results demonstrated that 3-D-MOSLMs have promise for full-colorized holographic 3-D displays.

Paleomagnetic recording fidelity of nonideal magnetic systems.

A suite of near-identical magnetite nanodot samples produced by electron-beam lithography have been used to test the thermomagnetic recording fidelity of particles in the 74–333 nm size range; the grain size range most commonly found in rocks. In addition to controlled grain size, the samples had identical particle spacings, meaning that intergrain magnetostatic interactions could be controlled. Their magnetic hysteresis parameters were indicative of particles thought not to be ideal magnetic recorders; however, the samples were found to be excellent thermomagnetic recorders of the magnetic field direction. They were also found to be relatively good recorders of the field intensity in a standard paleointensity experiment. The samples' intensities were all within ∼15% of the expected answer and the mean of the samples within 3% of the actual field. These nonideal magnetic systems have been shown to be reliable records of the geomagnetic field in terms of both direction and intensity even though their magnetic hysteresis characteristics indicate less than ideal magnetic grains.Key PointsNonideal magnetic systems accurately record field directionWeak-field remanences more stable than strong-field remanences