Thermomagnetic Recording Research Articles

Thermomagnetic recording characteristics of amorphous Tb-Fe /(BiY)<inf>3</inf>(FeGa)<inf>5</inf>O<inf>12</inf>

An amorphous Tb-Fe film of Fe-rich composition was directly overlayered to Bi substituted iron garnet films, (BiY) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeGa) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> and (BiYbSm) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeGa) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> to make a composite film for recording medium in thermomagnetic recording and magneto-optical read out system. In the optimum combination of a 1.2 μm thick Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">82</inf> film of 110 G in magnetization on a 0.85 μm thick (BiYbSm) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeGa) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> film, thermally recorded area as small as 1.5 μmφ in the former was exactly transcribed into the latter, and it still stayed stably under the magnetic field of 400 Oe with the opposite polarity. The reflectivity and poler Kerr rotation of the same film showed marked wavelength dependence accompanying large enhancement of polar Kerr rotation due to multiple reflection of incident light between the both interfaces, garnet film-GGG and garnet film-Tb-Fe film. Consequently, magneto-optical figure of merit was enhanced up to 1.2 deg. at λ=600 nm and 0.75 deg. at λ=700 nm which were ten and eight times larger than those of a Tb-Fe film, respectively.

Transmission electron microscopy of amorphous Fe-Tb thin films irradiated by pulsed laser beam

Amorphous Tb-Fe films were prepared on thin carbon films and glass substrates by r.f. sputtering method. They were irradiated by pulsed laser beams, the energy range of which was that commonly adopted for thermo-magnetic recording. Thermal effects were studied mainly by transmission electron microscopy. Structure of the irradiated areas changed from amorphous to crystalline, while magnetization of the corresponding area turned from perpendicular to in-plane orientation. Degree and diameter of a thermally influenced area depended largely on the film thickness over the range from 200 to 2000 Å. In a 500 Å Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</inf> film on a thin carbon substrate a circular area of 0.8 μm in diameter was crystallized by one 1 μs pulse of 2 mW. The damage was more evident in thinner films.

Energetics of domain formation in thermomagnetic recording

A new model for the distribution of perpendicular magnetization in thin magnetic films supporting a circular domain is proposed. The contributions of various sources to the magnetic energy are determined and the demagnetizing effect in particular is discussed at length. It is shown that a demagnetizing energy density per unit area of the domain wall can be defined which, unlike the domain wall energy density arising from exchange and anisotropy contributions, is a function of film thickness h. For domains of large radius and small wall thickness (compared with h), the demagnetizing energy density is found to be linearly increasing with h. A typical cycle of thermomagnetic recording on a thin ferrimagnetic film with room temperature compensation point is then studied, and the effect of various parameters on the formation process and stability of reverse magnetized domains is discussed.

熱磁気記録したＴｂ‐Ｆｅ膜の透過電子顕微鏡観察

Amorphous Tb-Fe films were prepared on thin carbon film and glass substrates by RF sputtering method. The films were irradiated with pulsed Ar laser beam, the energy range of which was that commonly adopted for thermo-magnetic recording. Thermal effects were studied mainly by transmission electron microscopy. The thermally influenced area depended largely on the film thickness over the range from 200 to 2000 Å. he structure of the irradiated areas changed from amorphous to crystalline, while magnetization of the corresponding areas turned from perpendicular to in-plane orientation. In a 500 Å Tb30Fe70 film on a carbon film substrate a circular area of 2.5 μm in diameter was crystallized by one 4 mW pulse of 1 μs. The damage was more evident in thinner films.

A new type of thermomagnetic recording on LPE garnet film

A new type of thermomagnetic recording using low coercivity LPE garnet film used as a bubble memory device and an Ar ion laser has been developed. The film has a logic capability which is, together with writing, readout and erasure, operated by the usual optical technique.

Thermomagnetic recording and reproducing apparatus

A heat magnetic recording and reproducing apparatus is disclosed. The apparatus comprises a record medium running in a predetermined direction, a means for generating a laser light beam for locally heating the medium, a magnetic field generating device for generating a magnetic field at the heated portion, an information recording means provided in opposition to the magnetic field generating device and having an auxiliary magnetic pole piece for focusing a magnetic flux from the magnetic field generating device into at least the heated portion, a means provided at a front stage of the information recording means to the running of the medium for generating a laser light beam for locally heating the medium, a magnetic field generating device for generating a magnetic field at the heated portion, and an information erasing means having an auxiliary magnetic pole piece for focusing a magnetic flux from the magnetic field generating device into the heated portion.

Garnet film with rectangular hysteresis loop and its application to thermomagnetic recording medium

Direct stacking of amorphous Dy-Fe and magnetic garnet layers resulted in a good medium for a thermomagnetic recording system. The composite film showed ten times larger optical rotation than the Dy-Fe film at λ = 550 nm. The minimum diameter of the transcribed domain from Dy-Fe layer into the garnet layer was 4 μ m.

Magnetic and optical properties of Co, Bi substituted garnet films prepared by the LPE method and its application to thermomagnetic recording

Co, Bi doped garnet films have a large Faraday rotation angle θ F in the visible region, and the uniaxial anisotropy K u and absorption coefficient α increases with Co substitution. Thermomagnetic recording threshold power is 4 mW for λ = 514.5 nm and irradiation time t = 10 μs, and 7.4 mW by coating of the Cr layer for λ = 632.8 nm and t = 2 μs.

Amorphous GdCo disk for thermomagnetic recording

Thermomagnetic recording was carried out on 150-mm-diam amorphous GdCo disks rotated at a speed of 1800 rpm. GdCo films showing good uniformity were deposited on glass disks by rf sputtering technique. Bits as small as 1 μm in width were recorded, making use of compensation temperature with a laser power of 5.6 mW and were read out with a laser power of about 2 mW. Thermal stability and dependence of the Kerr rotation angle on wavelength were also measured. It was confirmed that GdCo film is a most promising material for thermomagnetic recording.

A diffractometer with thermomagnetic recording for monitoring distortions of the wave front of the radiation of pulsed lasers

A diffractometer with thermomagnetic recording for monitoring distortions of the wave front of the radiation of pulsed lasers

Thermomagnetic Writing in Magnetic Garnet Films

The authors have succeeded in the development of rare-earth iron garnet (RIG) films whose magnetic coercivity is high enough to be used for Curie point writing. Specimens were prepared by means of liquid-phase epitaxial growth, where the lattice constant mismatch was set to be ∼0.04 Å. Sm and Er were used as rare-earth components to increase the coercivity through the enhancement of uniaxial anisotropy, while some amount of Bi was substitutes for them to strengthen the Faraday rotation. Optical and magnetic properties as well as thermomagnetic recording characteristics in the visible region have extensively been investigated. The writing threshold powers of a 0.55 µm thick film were found to be 51, 32 and 24 mW for wavelengths λ=514.5, 488.0 and 457.9 nm respectively, under laser irradiation for 10 µs with a spot radius of 2.5 µm. Analytical discussions are made based on the heat conduction in the recording medium.

Thermomagnetic video recording

Thermomagnetic recording of analog information on chromium dioxide tape has been investigated using apparatus consisting of a magnetic head and a laser as the heating source for writing and an inductive magnetic head for reproduction. A preliminary experiment indicated that the minimum recorded wavelength obtainable was about 3 μm and that a track width of less than 5 μm was possible. Another experiment, in which the tape was transported at a speed of about 10 m/s, showed the possibility of using thermoremanent techniques for real-time recording of video signals. Also it was demonstrated that magnetic printing techniques could be used to allow a magnetooptical readout of information recorded on the tape.

Properties of amorphous rare earth-transition metal thin films relevant to thermomagnetic recording

Properties of amorphous rare earth-transition metal thin films relevant to thermomagnetic recording

Amorphous GdCo Thin Films for High Density Thermomagnetic Recording

Experiments on the stability of small bits written in amorphous GdCo thin films were performed. It was confirmed that the bits written in films which are inhomogeneous along their thickness are stable and this stability did not decrease after many write-erase cycles with a laser beam. It can be concluded that amorphous GdCo thin films which are inhomogeneous along their thickness and have a compensation temperature near ambient are suitable for the high-density thermomagnetic recording application.

Thermomagnetic recording of data by an electron beam

An experimental investigation was made of the possibility of the thermomagnetie recording of data by means of an electron beam incident on epitaxial iron garnet films. Isolated points, 20 μ in diameter, as well as continuous lines were recorded.

Holographic storage of information in EuO films

An investigation was made of the use of thin EuO films as a medium for reversible optical storage of information. Very simple holograms, as well as images of a transparency containing 103 elements, were stored and reconstructed. The energy density of light pulses used in thermomagnetic recording was 5×10–5–5×10–6 J/mm2. Reconstruction (reading), performed with an He-Ne laser (λ = 0.63 μ), was characterized by an efficiency of 10–4 and the maximum spatial frequency exceeded 500 mm–1. An analysis was made of the possibility of improving the diffraction efficiency of reconstruction by means of radiation of 1150 nm wavelength.

Magnetic properties of amorphous Tb-Fe thin films prepared by rf sputtering

The magnetic properties of amorphous TbxFe1−x films prepared by rf cosputtering were studied. For 0.15&amp;lt;x&amp;lt;0.28, the films have uniaxial magnetic anisotropy normal to the film plane sufficient to stabilize cylindrical domains. The Curie temperature Tc and the coercivity Hc were measured as a function of composition. Tc increases monotonically with increasing Tb content in the alloy films in the region 0.1 &amp;lt; x&amp;lt;0.5. Hc is about one order of magnitude large, in contrast with amorphous Gd-Fe films at room temperature, and it increases further at low temperatures. Amorphous Tb-Fe films have a high potential for thermomagnetic recording using the Curie temperature because of the large Hc (1–5 kOe) and the low Curie temperature (∼120°C).

Thermomagnetic recording: Physics and materials

Thermomagnetic recording is the production of a remanent magnetization in a material by cooling it from a critical temperature in a small magnetic field. The most prominent applications for thermomagnetic recording presently under consideration are high density information storage and tape copying; other applications, e.g., display and magnetic printing, can also be envisioned. In this review of the field, we discuss the proposed applications of thermomagnetic recording, the physical principles of the various magnetic phenomena that can be used for this purpose, and the degree to which specific materials meet the requirements for thermomagnetic recording.

Stabilization of the high−temperature phase of MnBi by the addition of rhodium or ruthenium

It has been found that adding Rh or Ru to MnBi is effective in stabilizing the high−temperature β phase (distorted NiAs structure) relative to the low−temperature α phase (undistorted NiAs structure). This effect has been observed in both evaporated thin films and bulk samples. Addition of 1 at.% Rh to bulk MnBi increases the minimum time constant for the β→α transformation by 5 orders of magnitude. Stabilization is important in the use of MnBi for thermomagnetic recording.

Apparatus for measuring transient processes during thermomagnetic recording

An apparatus is described for measuring thermal and magnetization dynamics during thermomagnetic writing of information onto magneto-optic films. By probing various regions of the reversed spot, the spatial dynamics of bit formation can be reconstructed. The spatial resolution of the measurement is better than 1 μ and the intrinsic temporal resolution is 10 nsec. Representative results obtained with a ferrimagnetic and a ferromagnetic sample are included.