K. Kawanishi

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 A. 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.

Temperature dependence of perpendicular magnetic anisotropy in Co/Au and Co/Pt multilayers

Abstract Temperature dependences of perpendicular magnetic anisotropy and saturation magnetization in Co/Au and Co/Pt multilayer films prepared by rf sputtering method were investigated. The saturation magnetization, M s of the Co/Pt multilayer films is larger than M s of bulk Co at low temperatures. Enhancement of M s is not observed in Co/Au multilayer films. The magnetic anisotropy energy, K ⊥eff , of Co/Au multilayer films increases greatly with decreasing temperature. The K ⊥eff at 5 K is four times as large as that at room temperature in the Co(4 A)/Au(29.5 A) multilayer film. While K ⊥eff in the Co/Pt multilayer films decreases with decreasing temperature.

Magnetostriction of 3d‐transition metal/noble metal compositionally modulated multilayer films

Young’s modulus (Ef), magnetostriction (λf), stress (σ), and stress‐induced anisotropy (Ks) were measured in Co/Cu, Fe/Cu, Co/Ag, Co/Pd, and Co/Au compositionally modulated multilayer films (CMF) prepared by rf sputtering method. The measured values of Ef are almost equivalent to those of noble metals of Cu, Ag, Pd, and Au, respectively. The values of λf have an order of 10−5–10−6 which is the same order of the values in Co and Fe films. The calculated values of Ks from these results are about 10 to 100 times smaller than the measured values of perpendicular anisotropy (Ku) in the CMFs. Consequently, these results suggest that Ku of transition metal/noble metal CMFs cannot be explained only in terms of the stress‐induced anisotropy.

Magnetostriction and internal stress in GdFe amorphous films with perpendicular anisotropy prepared by RF diode sputtering

Abstract The influence of the substrate bias voltage (Vb) on the saturation magnetostriction (λs) and the internal stress (σ) were measured for rf sputter-deposited Gd-Fe films. The Vb dependence of the stress induced anisotropy Ks ( = -3/2λsσ) is similar to that of Ku in the lower Vb region.

Growth induced magnetic anisotropy in Co-doped garnet and its capability of application to magneto-optical memory materials

Growth-induced magnetic anisotropy (Kug) normal to the film surface in Co-doped iron garnet films grown on GGG substrates by the LPE method has been quantitatively discussed. Kug is increased with increasing Co content and growth rate (Vg). From the measurement of temperature dependence of magnetocrystalline anisotropy K 1 , the parameter αλ is evaluated to be 80 cm-1through a curve fitting procedure using Slonczewskis theory of Co single-ion model for the anisotropy. After the annealing at temperatures above 900°C, Kug is disappeared and K 1 is increased: These changes are successfully interpreted by the theory using the above value αλ. Also shown is the magnetic field effect on the perpendicular anisotropy of poly-crystalline Co-doped BiDyGeIG films prepared by the pyrolysis method on glass substrates for the purpose of application to magneto-optical memory materials. In these films, (Ge(CH 2 ) 2 COOH) 2 O 3 is found to be a suitable solute for adding tetravalent Ge ions. In this method, an increase of Co amount raises the crystallization temperature, while doping of Ge lowers it. A magnetic field perpendicularly applied to the film during the heat treatment for crystallization enhances the anisotropy, whereby Ku is increased to about 170% of those of films prepared with no field.

Guided-wave properties and mode conversions in (BiNdLu) 3 (FeAlLu) 5 O 12 films

The guided-wave properties and TE-TM mode conversions for LPE-grown (BiNdLu) 3 (FeAlLu) 5 O 12 films were studied. A complete (100%) TE-TM mode conversion efficiency was attained by controlling the stress- and growth-induced optical birefringences which seriously influence the phase matching between the TE and TM modes. The mode conversion saturated under an external magnetic field at less than 8 Oe parallel to the light propagation direction. The correlation between growth-induced birefringence and growth-induced uniaxial magnetic anisotropy is discussed. It was found that the magnetooptical figure of merit |θ F |/α reached more than 160 deg/dB at wavelength λ=1.15μm. These results show that (BiNdLu) 3 (FeAlLu) 5 O 12 films are promising materials for waveguide-type magneto-optical application.

Optical and magneto-optical characteristics at 1.54µm of Co, Ge doped YNdIG LPE garnet films

Contribution of the Co ion to the growth-induced uniaxial magnetic anisotropy (Kug) has been observed in Co,Ge substituted yttrium-neodymium-iron garnet films grown on GGG substrates by the LPE method. Kug of the films on

The medium noise reduction by intensity dividing readout in the magneto-optical memories

Medium noises in a magneto-optical memory are analytically discussed on an experimental basis. We propose the intensity dividing readout (IDR) method for the reduction of medium noise. The IDR method has the following merits: (1) Noises caused by intensity fluctuation can be cancelled out, (2) the carrier-to-noise ratio (C/N) becomes insensitive to an analyzer angle (φ) and reaches a maximum when φ is 45°, (3) in addition, the current gain (M) of the avalanche photo diode (APD) can be lowered, because it receives a maximum light intensity when φ=45°. Consequently, IDR method does not need any fine adjustment of sensitivity, input power and φ of detectors.

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

Abstract 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 .

Design and Computer Simulation of Magnetic Bubble Domain Current-Access Major/Minor Loop Organization

A major/minor loop organization has been designed by using dual-conductor sheet devices. The design was carried out by consulting the drive-field distribution obtained on scaled-up models of the conductor sheets and the results of computer simulation. A device configuration has been obtained which has a fairly good operating margin for all of the necessary operations, including propagations along the minor loop and major line, minor-loop cornering, and transfer-in/out operations. This paper describes the method of drive-field measurement, the process of device improvement, an outline of the simulation method and the results of performance evaluation by computer simulation.