Magneto-optical Recording Research Articles

The structural, morphological, optical, thermal and magnetic properties of MnFe2O4 nanoparticles

In this study manganese ferrite (MnFe2O4) nanoparticles were synthesized using a simple co-precipitation method. The nanocomposite was designed to achieve a cubic spinel structure with particle sizes between 21-35 nm, confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM). The magnetic properties, investigated using a vibrating sample magnetometer (VSM), shows the superparamagnetic behavior. The optical band gap was found by quantum size effects, by UV-Vis spectroscopy. This nanocomposite shows potential applications in magnetic and magneto-optical recording devices because of its optimized magnetic and optical properties.

Magneto–Optical Properties and Applications of Magnetic Garnet

The interaction between light and the magnetization of a material is called the magneto–optical effect. It was used in magneto–optical recording such as MO disks and has been applied to optical isolators etc. with the development of optical communications. The magneto–optical properties of magnetic garnets and their applications are briefly reviewed in this article. In the first half, after a brief overview of the phenomenology of the magneto–optical effect, the effects of element substitution on properties such as Faraday rotation and optical absorbance of magnetic garnets are shown. In the second half, some interesting applications such as imaging technologies and other novel applications using the magneto–optical effect of magnetic garnets are also introduced.

Development of Fabrication Techniques for Magneto-Optical Diffractive Deep Neural Networks

Magneto-optical diffractive deep neural network (MO-D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> NN) is a type of diffractive deep neural network that utilizes the magneto-optical effect of magnetic materials. MO-D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> NN is composed of magnetic material, which is non-volatile and allows neurons to be rewritten. In our work, we fabricated and evaluated MO-D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> NN with 2 layers containing 100 × 100 magnetic domains with a domain size of 1 μm. Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> GaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> thin films were prepared on the both sides of a Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> substrate and magnetic domain patterns were recorded using the magneto-optical recording technique. The recording accuracies of first and second layer were 79% and 70%, respectively. We believed that magneto-optical recording technology can achieve a recording accuracy of over 90% by optimizing the fabrication and recording conditions. The optical setup was built and handwritten digit classification was carried out using fabricated MO-D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> NN, but the number of classifications was lower than in the case of simulation. We considered that recording errors were responsible for the low number of classifications and assessed the effect of recording errors on accuracy by simulation. When the recording error was lower than 10%, the loss in classification accuracy was found to be only ~3%. Therefore, we are convinced that MO-D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> NN has high physical implementation potential.

Effect of ZnO on the Structural and Magnetodielectric Properties of MgFe2O4 Nanocomposite Prepared by Sol-Gel Method

Zinc oxide doped magnesium ferrite (Mg1-xZnxFe2O4) nanocomposite was synthesized using sol-gel method and demonstrated to have a cubic spinel structure, with a range of crystallite sizes (19-40 nm) and lattice constants (8.432-8.399 Å). The material was found to have two prominent vibrational modes for tetrahedral (446 cm–1) and octahedral (584 cm–1). The dielectric constant was higher at low frequencies and decreased at higher frequencies, while the saturation magnetization decreased (16 to 6 emu/g) gradually with an increase in Zn2+, likely due to the presence of non-magnetic Zn2+. The magneto-dielectric constant was found to increase with the magnetic field for MgFe2O4 and up to a magnetic field of 2000 Oe for the zinc magnesium nanocomposites, after which it decreased for higher magnetic fields. A positive and negative change in magneto-capacitance as a function of the magnetic field was also observed. The antibacterial activity suggests that the substitution of Zn2+ into magnesium ferrite can be an effective method for improving antibacterial activity, with the potential to damage the bacterial membrane and other components through positively charged ions and ROS generated by nanoparticles. Potential uses for this synthetic material include magneto-optical recording and magnetic biosensors.

Photo-switching of magnetoresistance in p-Co3O4/n-WS2 heterojunction

Tuning and controlling magnetic states by light is of great interest for applications such as magneto-optical recording and sensing devices. In this research, the change of sign and adjustability of magnetoresistance by light is shown experimentally. In a simple device, a p-n junction is created at the interface of a thin layer of n-type WS2 and p-type Co3O4. The device displays positive magnetoresistance in the dark, while under light illumination, it displays negative magnetoresistance. We suggest that this effect may be due to the suppression of photogenerated electron-hole recombination under the Zeeman effect. The findings of this research can lead to the development of practical fields such as light sensor systems or magnetoresistance memory devices of the new generation.

Comparative study of femtosecond laser-induced ultrafast magnetization dynamics in soft ferromagnetic ultra-thin alloy

The typical demagnetization mechanism is applicable in magneto-optic recording systems on a nanoseconds timescale. Interest in this area has expanded rapidly since understanding the physics of ultrafast magnetization processes by experiment are an acutely challenging task. As a result, in order to explain the quenching of magnetization by laser heating in ferromagnetic alloys such as permalloy, we executed a new theoretical study on permalloy, as well as Ni and Fe ultra-thin films with thickness varying from 1 nm to 5 nm. In particular, we demonstrate that the magnetization decays in a timescale of about 0.1 picosecond by the microscopic three-temperature model. Our free electron model-based theoretical model represents that electron–phonon coupling coefficient and demagnetization time in the thin-films are strongly sensitive to film thickness, pulse duration and laser fluence, respectively. In particular, we show that the rapid demagnetization (100 fs) is due to electron-magnon excitation. This feature improves data processing speed in communication systems and the recording industry.

Reflecting upon some electromagnetic waves in a ferromagnetic film via a variable-coefficient modified Kadomtsev-Petviashvili system

Kadomtsev-Petviashvili-type models are employed in magneto-optics, ferromagnetism, plasma physics, fluid mechanics, etc. For a variable-coefficient modified Kadomtsev-Petviashvili system modelling the electromagnetic waves in an isotropic charge-free infinite ferromagnetic thin film, exciting the magnetization and with the potential application in magneto-optic recording, we symbolically compute out two sets of the similarity reductions, each of which can be from that system to a known ordinary differential equation. Both sets rely on the constant/variable coefficients for that system.

Field-Free Magnetoplasmon-Induced Ultraviolet Circular Dichroism Switching in Premagnetized Magnetic Nanowires.

Broadband modulation of magnetic circular dichroism (MCD) using a relatively low magnetic field or by producing a field-free magnetoplasmonic effect in the remnant magnetic state was achieved by the integration of the noble metals (NMs) Au and Ag and the perpendicular magnetic anisotropy of Co with ZnO nanowires (NWs) used as the template. The samples containing NMs revealed MCD sign reversals and enhancements when compared with the original Co/ZnO NWs. The magnetoplasmonic effect of Au close to the visible light spectrum could induce the CD change in the visible region. Notably, the ultraviolet (UV) CD in Ag/Co/ZnO NWs is 12.5 times larger under a magnetic field (∼0.2 T) and 10 times greater in the remnant state (field-free) than those of the original Co/ZnO NWs because of the magnetoplasmonic effect of Ag in the UV spectrum. These results are attributable to the coupling of the remnant magnetic state of Co magnetization, the magnetoplasmons of the NMs, and the excitons of the ZnO NWs. The findings are potentially applicable in magneto-optical recording, biosensing, and energy contexts involving magnetoplasmonic functionalization.

Certain electromagnetic waves in a ferromagnetic film

Electromagnetic-wave/ferromagnetic-material investigations with magneto-optics are carried out in magneto-optic recording, computer data-storage, waveguides, etc. In this paper, we investigate a variable-coefficient modified Kadomtsev–Petviashvili system for certain electromagnetic waves in an isotropic charge-free infinite ferromagnetic thin film with the potential application in magneto-optic recording. With respect to the electromagnetic waves in the ferromagnetic film, symbolic computation helps us work out (1) two sets of the variable-coefficient-dependent auto-Bäcklund transformations via the generalized Laurent series, along with some solitonic features, (2) one set of the variable-coefficient-dependent bilinear forms and (3) two sets of the variable-coefficient-dependent N-solitonic solutions with N being a positive integer. We note that the electromagnetic field can excite the magnetization of a ferromagnetic medium in the form of solitons with the applications in magneto-optic recording. Relevant constraints on the variable coefficients are presented. We hope that the results could help the studies on magneto-optic recording, computer data-storage and waveguides.

Spin compensation, critical and discontinuous transitions behaviors in a ferrimagnet of spins 5/2 and 7/2

We apply Monte Carlo simulation techniques to study the magnetic behavior of a mixed ferrimagnetic Ising model on sites of a square lattice of LxL size, with L = 120, where 5/2 spins are alternated with 7/2 spins. We consider an antiferromagnetic interaction next-neighbor, ferromagnetic interactions next-nearest-neighbor, and an external magnetic field in the Hamiltonian that defines the model. We characterize the effects of an external magnetic field on the behavior of the system through the analysis of spin compensation points, discontinuous transitions, and hysteresis loops at various temperatures in the total magnetization and magnetic susceptibility. At the end, we study the phase diagrams of the critical, compensation and discontinuous transition temperatures. The physical phenomena experienced by the system under study are relevant to the application in magneto-optical recordings, in the synthesis and construction of molecular-based magnets and have technological applications in the manipulation and storage of magnetic information. We found some phenomena not reported in previous works on the same system.

Magneto-optical design of anomalous Nernst thermopile

The introduction of spin caloritronics into thermoelectric conversion has paved a new path for versatile energy harvesting and heat sensing technologies. In particular, thermoelectric generation based on the anomalous Nernst effect (ANE) is an appealing approach as it shows considerable potential to realize efficient, large-area, and flexible use of heat energy. To make ANE applications viable, not only the improvement of thermoelectric performance but also the simplification of device structures is essential. Here, we demonstrate the construction of an anomalous Nernst thermopile with a substantially enhanced thermoelectric output and simple structure comprising a single ferromagnetic material. These improvements are achieved by combining the ANE with the magneto-optical recording technique called all-optical helicity-dependent switching of magnetization. Our thermopile consists only of Co/Pt multilayer wires arranged in a zigzag configuration, which simplifies microfabrication processes. When the out-of-plane magnetization of the neighboring wires is reversed alternately by local illumination with circularly polarized light, the ANE-induced voltage in the thermopile shows an order of magnitude enhancement, confirming the concept of a magneto-optically designed anomalous Nernst thermopile. The sign of the enhanced ANE-induced voltage can be controlled reversibly by changing the light polarization. The engineering concept demonstrated here promotes effective utilization of the characteristics of the ANE and will contribute to realizing its thermoelectric applications.

Light-induced radially polarized magnetic fields

Many ferromagnets exhibit the inverse Faraday effect (IFE), and based on the IFE, magnetic fields with different distributions can be induced conveniently in these ferromagnets by tailoring the laser fields. Besides, the magnetic field induced by IFE has been conceived as a far-field and non-invasive method to manipulate the magnetization. Up to now longitudinal magnetic fields, transverse magnetic fields and even a vector magnetic field, where its polarization is along the azimuthal direction, have been generated. However, another vector magnetic field, where its polarization along the radial direction has not been reported yet. In this paper, by focusing two counter-propagating cylindrical vector beams (CVBs) in a 4Pi tightly focusing system, we theoretically tailor the polarization and distribution of the highly confined focused electric field, and a radially polarized magnetic field (RPMF) is generated in the focal plane through the IFE. This RPMF can facilitate the development of the technology of magneto-optical recording. The distribution of induced magnetization in the defocus plane of the 4pi tightly focusing system is also surveyed in this paper.

Synthesis of Vanadium Ferrite Nanoparticles By Microwave Assisted Technique

Among the magnetic materials ferrites are of great interest due to its distinctive properties. Ferrites exhibit a spontaneous magnetic moment below a Curie temperature and act as insulators at low temperature. Sincethey have been used in number of technological applications like microwave devices, magnetic and magneto optic recording, data storage etc. The incredible magnetic, electric and dielectric properties of ferrites make them more attractive and applicable in the current field of science and technology. In the present study vanadium ferrite nanoparticles were synthesized by microwave assisted method. The structural properties of synthesized nanoparticles are carried out from X-ray diffraction technique. The presence of peaks confirms the crystalline nature of the vanadium ferrite nanoparticles. The crystal structure, crystalline size (D), Dislocation density (8) is determined from XRD data. Also using Williamson-Hall plot micro strain value is calculated.The different molecular vibrations are confirmed through Fourier Transformed Infrared Spectroscopy (FTIR) vibration spectra. From the Ultra Violet Spectroscopicdata using the Tauc relation, the energy gap (Eg) at the edge of absorbance band is calculated as 4.28eV for direct and 4.84 eV for indirect transition. The morphological studies are done through Scanning Electron Microscope (SEM). From the SEM micrographs we confirm the presence of spherical nanoparticles and they are arranged uniformly. From VSM analysis, we calculated the saturation magnetization as 20.00 emu, coercivity as 125.96 g, and retentivity is 130.45 emu.

Magneto-optical/ferromagnetic-material computation: Bäcklund transformations, bilinear forms and [formula omitted] solitons for a generalized (3+1)-dimensional variable-coefficient modified Kadomtsev–Petviashvili system

Of current interest, magneto-optics deals with the phenomena associated with magnetic effects on matter as it emits light, having the potential applications in computer data-storage and waveguides, while ferromagnetic materials are the ones displaying ferromagnetism, such as the various forms of iron, steel, cobalt, nickel, and their alloys. In this paper, in magneto-optics, ferromagnetism, fluid mechanics and plasma physics, we investigate a generalized (3+1)-dimensional variable-coefficient modified Kadomtsev–Petviashvili system for the electromagnetic waves in a ferromagnetic material, or water waves, or dust-acoustic/ion-acoustic/dust–ion-acoustic waves in a plasma. Special cases of the system in those fields are listed out, such as one special case in magneto-optics, which describes the electromagnetic waves in an isotropic charge-free ferromagnetic thin film with the potential application in magneto-optic recording. With symbolic computation, we work out (1) two sets of the variable-coefficient-dependent auto-Bäcklund transformations along with some solitonic features, (2) the variable-coefficient-dependent bilinear forms with the Hirota method and (3) two branches of the variable-coefficient-dependent N-soliton solutions with N being a positive integer. Relevant constraints on the variable coefficients are presented.

Impact of Different Set of Precipitants on the Formation of BaFe12O19 Phase Nanomaterials.

This work deals with the preparation of BaFe12O19 materials by soft chemical co-precipitation method using a different set of precipitants namely, (i) NaOH and Na₂CO₃, (ii) NH₂CONH₂ and NH₄OH, and (iii) NH₄HCO₃ and NH₄OH. The influence of these precipitants on the different properties is also investigated by various characterizations. The precipitants used in this work considerably affected the phase formation of BaFe12O19 materials. The thermal analyses reveal the thermal decomposition of the intermediate phase as well as the crystallization of BaFe12O19 phase. Due to the amorphous nature, all the co-precipitated products were annealed for 2 h at 1000 °C. Among the different annealed samples, the NaOH and Na₂CO₃ set of precipitant derived materials exhibit nearly single hexagonal phase of crystalline BaFe12O19 nanomaterials with an average crystalline size of ˜48 nm with a = 0.5888(4) nm and c = 2.320(2) nm. The particle size observed in micrograph was rather much higher than the average crystalline size obtained from XRD for the best sample. The BaFe12O19 nanomaterials studied in the present work have been found potential applications in magneto-optic recording media, biomolecular separations, magnetic carriers for drug targeting, permanent magnet, chip inductors, microwave absorbers, and hyperthermia cancer treatment.

Effect of Zinc Content on Structural, Functional, Morphological, Resonance, Thermal and Magnetic Properties of Co1−xZnxFe2O4/PVP Nanocomposites

Integrate Zinc substituted cobalt ferrites have incorporated by the Co-precipitation technique. The XRD pattern shows the formation and microstructure evolutions of nanocomposites. Cationic coordination, exchange interactions raised between the tetrahedral site in high frequency and octahedral site in the lower frequency described FTIR results. The SEM images showed that the spongy morphology with PVP matrix and fewer agglomerated grains. It exposes the grains and the range of grains recovered from 1μ to 400 nm, which is in compromise with the test of grain size of XRD. VSM study reveals that the magnetization of substances raises by incrementing the non-magnetic (Zn) material incorporated cobalt ferrite. EPR confirmed that synthesized materials exhibited ferromagnetic properties from Lande g-factor. TGA/DSC curve reports the weight loss and heat flow by endothermic absorption through exothermic emission in the ferrite. It used these materials for the potential effort like magneto-optical recording media and magnetic sensors.

Characterizing magnetization reversal processes of GdFeCo film in the vicinity of the spin reorientation transition temperature

An amorphous GdFeCo film has a spin reorientation transition (SRT) with the temperature varying from 230 K to 300 K. Its magnetization reversal processes have been characterized by the hysteresis loops and first-order reversal curve (FORC) in the vicinity of the SRT temperature. Along with the SRT from out-of-plane to in-plane, the total irreversible components decrease with increasing temperature from 84% (250 K) to 13% (300 K) and the reversal process gradually changes from the pinning-type dominated reversal (250 K) to the nucleation type reversal (270 K), and then to the uniform rotation (300 K). The identification of the magnetization reversal process nearby SRT is important to understand the magnetic properties in the magneto-optical recording materials GdFeCo.

Tailoring of Perpendicular Magnetic Anisotropy in Dy13Fe87 Thin Films with Hexagonal Antidot Lattice Nanostructure.

In this article, the magnetic properties of hexagonally ordered antidot arrays made of Dy13Fe87 alloy are studied and compared with corresponding ones of continuous thin films with the same compositions and thicknesses, varying between 20 nm and 50 nm. Both samples, the continuous thin films and antidot arrays, were prepared by high vacuum e-beam evaporation of the alloy on the top-surface of glass and hexagonally self-ordered nanoporous alumina templates, which serve as substrates, respectively. By using a highly sensitive magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements an interesting phenomenon has been observed, consisting in the easy magnetization axis transfer from a purely in-plane (INP) magnetic anisotropy to out-of-plane (OOP) magnetization. For the 30 nm film thickness we have measured the volume hysteresis loops by VSM with the easy magnetization axis lying along the OOP direction. Using magnetic force microscopy measurements (MFM), there is strong evidence to suggest that the formation of magnetic domains with OOP magnetization occurs in this sample. This phenomenon can be of high interest for the development of novel magnetic and magneto-optic perpendicular recording patterned media based on template-assisted deposition techniques.

Theoretical investigation of the structural, optical and magnetic properties of Mn doped and (Mn, Cr) co-doped CdS in its cubic structure

The electronic, magnetic and optical properties of doped CdS:Mn and co-doped CdS:Mn, Cr cubic structures were studied via Density Functional Theory and subsequently compared with the properties of undoped CdS. The doped compound presents semiconducting character similar to the undoped CdS, while the co-doped compound exhibits half metallic properties with a high spin polarization at the Fermi energy. The magnetic moments as well as the trend of magnetic exchange parameters of CdS:Mn and CdS:Mn,Cr, have been analyzed, in addition to the dielectric functions, by starting from calculated density of states for spin polarized configurations. The calculated absorption coefficients lead to direct information on the spectral energy distribution in the range of optoelectronic applications. The optical band gaps of doped and co-doped compounds are higher as compared to the undoped CdS, making the first compounds more interesting for possible technological applications for high density magneto-optical recording.

光磁気記録における新たな(1,7)RLL符号化PRML方式

光磁気記録における新たな(1,7)RLL符号化PRML方式