Magneto-optical Recording Materials Research Articles

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.

ChemInform Abstract: Corrosion Mechanism of Sputter-Deposited TbFe Thin Films in Aqueous Environment.

This paper reports on the corrosion mechanism of sputter-deposited TbFe thin films for magneto-optical recording material that was investigated using electrochemical methods in aqueous environment with and without Cl{sup {minus}} ions. TbFe thin films with varying composition prepared by an ion beam sputtering method were used as specimens. TbFe tape alloys made by the rapid quench method of melting alloys were also used for comparison. In an acid buffer solution without Cl{sup {minus}} ions, the corrosion rate of the TbFe thin films and tape alloys decreased with increasing Tb content. In this solution, passive films composed of Tb oxide or hydroxide were formed on both the TbFe thin films and tapes and the selective dissolution of Fe through the passive films occurred. In neutral solutions with Cl{sup {minus}} ions, pitting corrosion occurred on both the TbFe thin films and tapes. The stoichiometric dissolution of the substrate at pitted sites and the selective dissolution through the passive films at nonpitted sites take place in these solutions.

The effect of boron on the uniaxial magnetic anisotropy energy and the polar Kerr rotation in amorphous NdFe films

Amorphous light rare earth–transition metal alloys are candidates for magneto-optical recording materials in the wavelength region of a blue laser beam (λ≈400 nm) due to the large Kerr rotation angle θK. However, the large demagnetizing energy (shape anisotropy) prevents the films from developing an effective perpendicular anisotropy. The addition of boron to the amorphous Nd Fe matrix reduces the magnetization, enhances the effective perpendicular anisotropy, and enhances the Kerr rotation angle θK.

Thermal Stability of Domains in Magneto-Optic Recording Materials

Thermal Stability of Domains in Magneto-Optic Recording Materials

Present and future of magnetooptical recording materials and technology

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.

The creation of nanometer magnetic domain structure in 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.

Time-dependent effects in materials with two-stage reversal processes

We have measured the magnetic viscosity in materials which undertake magnetisation reversal by two distinct processes. The materials examined were Pt/Co multilayer systems which have potential as magneto-optic recording materials. In these systems magnetisation reversal proceeds first by the nucleation of a reverse domain followed by the propagation of the domain wall. Thus, in materials where the domain wall pinning is strong two distinct regions of reversal occur. In consequence, we observe two different forms of variation of magnetisation with time and additionally different values for derived parameters such as the fluctuation field.

MAGNETO-OPTICAL PROPERTIES OF Co-AND Ti-SUBSTITUTED BARIUM HEXAFERRITE FILMS PREPARED BY THE SOL-GEL METHOD

Optical and magneto-optical properties of several single and layered Co-, Ti- and Al-substituted hexaferrite thin films prepared by the sol-gel method were investigated. The Faraday coefficient exhibits pronounced extrema in the infrared and visible part of the spectra. Broad maxima of the figure of merit at 700 to 900 and 1400 to 1800 nm regions show that some of the materials could be considered as the candidates for magneto-optical recording materials at interesting laser wavelngths of 800 and 1500 nm.

Thin Films for Secondary Data Storage

This paper reviews the evolution of magnetic thin films and their processing for use in secondary data storage devices like hard disks, floppy disks, CD-ROM and magneto-optic disks. High recording density and low cost in commercially available high capacity hard disks and CD-ROM's have been made possible due to use of thin film materials in these devices. The work on magneto-optic recording materials based on amorphous Tb-Fe-Co alloy thin films leading to its recent commercialization is discussed. To overcome the shortcomings of Tb-Fe-Co like poor oxidation resistance and no direct rewrite capability, efforts to use newer materials like garnet thin films and multi-layer thin films are also described.

Magnetic and magneto-optical properties of CoPtM (M = Re, Ru) alloy films for a new magneto-optical recording material

CoPtM (M = Re, Ru) ternary alloy films have been investigated as new magneto-optical materials for blue laser recording. The CoPtRe and CoPtRu alloy films were prepared by sputtering without a heating process, and exhibited good perpendicular magnetic anisotropy and magnetic hysteresis loop squareness. For the magneto-optical properties, the figure of merit for the CoPtRe alloy film with less than 15 at% Re at λ < 530nm is shown to be superior to that for TbFeCo amorphous film and inferior 0–4 dB to that of Co/Pt multilayers.

Examination of magneto-optic transverse Kerr effect measurements in thin magnetic films exhibiting perpendicular anisotropy

A uniaxial perpendicular magnetic anisotropy is perhaps one of the most important properties exhibited by thin film materials suitable for high-density magneto-optic recording disks. Previous works report studies of this anisotropy in amorphous rare earth-transition metal (RE-TM) alloys using measurements of the polar Kerr magneto-optic effect to provide the basic data. The experimental data so obtained is complementary to that usually provided by torque and VSM magnetometry but are sometimes difficult to analyse and not always unambiguous. The authors describe an examination of the data provided by the transverse Kerr magneto-optic effect in an attempt to provide further useful information concerning the nature of the anisotropy in magneto-optic recording materials.

NdFeCo TRILAYER AMORPHOUS FILMS WITH HIGH KERR ROTATION AT SHORT WAVELENGTHS

Magneto-optical recording materials with high remanent Kerr rotation at short wavelengths were successfully obtained in a trilayer form. A NdFeCo amorphous film with in-plane magnetization, but with a large saturation Kerr rotation angle at short wavelengths, was sandwiched between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The trilayer film, Tb20Fe74Co6 (10 nm)/Nd16Fe57Co27 (7.5 nm)/Tb20Fe74Co6 (100 nm), shows a remanent Kerr rotation angle θKr = 0.32° at a wavelength of 400 nm, coercivity Hc = 2.4kOe, and a good square loop (θKr/θKs ∼ 1).

Ultrathin Co/Pt and Co/Pd Multilayers as Magneto-Optical Recording Materials

Ultrathin Co/Pt and Co/Pd Multilayers as Magneto-Optical Recording Materials

Evalution of Practical Application Characteristics for New Magneto-Optical Recording Medium MnBiAlSi

Quasi-dynamic thermomagnetic write/read/erase and lifetime experiments on new magneto-optical recording material MnBiAlSi film which has a singnificant Kerr rotation angle have been achieved for the first time and the characteristics with practical application worth have been also initially obtained. As a result, it is a promising material for the magneto-optical disc use.

Novel magneto-optical recording materials: Bi-substituted garnet films

For future high density magneto-optical recording materials, a Bi-substituted garnet film ((BiDy)3(FeGa)5O12) is an attractive candidate since it has strong magneto-optic effect at short wavelengths less than 600 nm. The signal in read back performance at 500 nm using a garnet film can be an order of magnitude higher than a current rare earth-transition metal amorphous film. However, the granularity and surface roughness of such crystalline garnet films are the key to control for minimizing media noise.We have demonstrated a new technique to fabricate a garnet film which has much smaller grain size and smoother surfaces than those annealed in a conventional oven. This method employs a high ramp-up rate annealing (Γ = 50 ~ 100 C/s) in nitrogen atmosphere. Fig.1 shows a typical microstruture of a Bi-susbtituted garnet film deposited by r.f. sputtering and then subsequently crystallized by a rapid thermal annealing technique at Γ = 50 C/s at 650 °C for 2 min. The structure is a single phase of garnet, and a grain size is about 300A.

Japan, magnetism, and technological competition (invited) (abstract)

Magnetism has been the fountainhead of ideas for understanding cooperative phenomena and magnetics is at the foundation of $60 billion of annual trade (Mallinson). And yet, led by the National Science Foundation, the federal science contracting agencies years ago dropped support of magnetism and magnetics. A few months ago I returned from 3 years in Tokyo as an ONR scientific cooperation and exchange officer, monitoring magnetism and superconductivity. Unlike the Americans, the Japanese, traditionally very strong in magnetics, continue to concentrate resources there. World-wide sales of magnetically soft electrical steels come to $5 billion/year. The US is now the largest external buyer of Japanese electrical steel. One million tons (over $1 billion) of top grade, grain oriented (GO) silicon steel are shipped annually. Half the world’s GO steel is produced by Nippon Steel (25 000 tons/month) and Kawasaki Steel (15 000 tons/month). In perpendicular magnetic recording (PMR) the Japanese are pre-eminent. Of the 342 attendees at the first Conference on PMR last year, less than 50 were Westerners. Co-Cr and Ba ferrite are now Japanese stories. In magneto-optics the Japanese are dominant. Twenty-five universities have had Monbusho-funded programs in magneto-optical recording materials, and MITI is building industry/university cooperative R&amp;D laboratories on the campuses. The U.S. can and has to learn some things from Japan. I will offer a number of suggestions in the talk.

Triple-layered NdCo amorphous-alloy films for magneto-optical media

Magneto-optical recording materials with high remanent Kerr rotation at a short wavelength were successfully obtained in a trilayer form. NdCo amorphous films with an in-plane magnetization were sandwiched between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The thickness of the top layer of the TbFeCo film facing an incident laser beam is less than the light-penetration depth. Triple-layered films [Tb18Fe49Co33 (5 nm thickness)/Nd18Co82(10 nm)/Tb18Fe49Co33(200 nm)] thus obtained show a remanent Kerr rotation angle θKr = 0.37°–0.46° at wavelength λ=400–850 nm, coercivity Hc = 2 kOe, and good square loop (Mr/Ms = 1). The figure of merit √R̄θK, where R is reflectivity, is 0.24–0.31 at λ=400–850 nm, which is higher than that of conventional TbFeCo amorphous films (√R̄θK = 0.12–0.27 at λ=400–850 nm).

MAGNETO-OPTICAL MEDIA WITH HIGH KERR ROTATION AT SHORT WAVELENGTHS

Magneto-optical recording materials with high remanent Kerr rotation at short wavelengths were successfully obtained in a trilayer form by sandwiching NdCo amorphous films with an in-plane magnetization between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The effect of the NdCo thickness on the magnetic and magneto-optical properties of the trilayer medium was investigated systematically. The distribution of the magnetization direction in a trilayer NdCo amorphous alloy film was calculated to manifest the reorientation of the magnetization inside the NdCo layer through magnetic exchange coupling.

磁気・光磁気記録材料への誘い

This is to introduce physical backgrounds on magnetic and magneto-optical recording materials. Firstly, for each theme, fundamental configuration and its function is given. For magnetic recording, the single magnetic domain model, i.e., coherent rotation of magnetization is based on magnetic media and heads, which are applicable for recent items. It is presented that a high coercivity is required for the media from a viewpoint of high density magnetic recording. Special attention is put on a correlation between switching field distribution, SFD in the magnetization reversal and magnetic transition region between recorded domains, which leads to a development principle on materials of recording media. For magnetic heads with magnetic thin film, it is introduced that a decrease in local fluctuation of magnetic anisotropy due to grain size and its distribution is essential function for obtaining a high permeability at 10MHz range. For magneto-optical recording materials, an emphasis is in magnetic multilayer configuration in the recording media for realizing high access time in a disk operation which results in direct overwriting methods. Magnetic field- and light-modulation methods for overwriting are introduced. These contribution due to the film configurations is briefly described.

Domain erasure and formation in direct overwrite magneto-optic recording

The erase and write processes in single layer direct-overwrite magneto-optic recording materials were investigated utilizing a stroboscopic microscope system with 10-nsec time resolution. The effects of thermal magnetization reduction are addressed and limited by image subtraction techniques. With this technique the erase process is shown to be a collapse process which occurs during heating, rather than cooling. Galvanometer driven beam scanning is utilized to write and erase ‘‘stripe’’ domains at velocities up to 5 m/s. Scanning write and scanning continuous beam erase are investigated stroboscopically, providing surprising new data on these processes. The erase process for a ‘‘stripe’’ domain is shown to proceed from the end of the domain, and in front of the approaching erase laser beam. Jitter in the leading edge of the written domain is observed, and may be responsible for the noise levels observed in these materials. The data indicate that the erase process is driven by a combination of temperature and temperature gradient. The write behavior can be explained by either a post-laser pulse nucleation or by movement of the trailing domain wall.