H. Matsuda

Recording experiments in magneto‐optical disks using ultrathin Co/Pt and Co/Pd media

Magneto‐optical media using ultrathin Co/Pt and Co/Pd films were prepared on 2P (photopolymer) glass substrates with a double‐layer disk structure. Thermomagnetic writing was successfully made in the magneto‐optical disks by the relatively low laser power above 3 mW. The values of the C/N ratio were 50 dB for the Co/Pt disk and 45 dB for the Co/Pd disk at a bit length of 5 μm. Clear and regular bit domains were observed even in the shorter recorded bit length.

Magnetic and other properties and sputtering behavior of Co‐base amorphous alloy films

Magnetic and other properties of Co‐base amorphous alloy films prepared by sputtering are investigated. A detailed magnetic phase diagram with saturation magnetic flux density, crystallization temperature, and zero‐magnetostrictive line on Co‐Ta‐Zr amorphous alloys were obtained, and the technical knowhow to make a film with well‐reproducible characteristics by widely changing the sputtering conditions was related with these physical properties. Especially on alloy sputtering, a phenomenological model for elucidating a composition difference between film and target is presented. After these studies, the film characteristics of Bs=12 kG, Tx=450u2009°C, ‖λs‖<10−8, Hc<10 mOe, and permeabilities of μ(1 MHz)=7000, μ(100 MHz)=2000 for the single film of 2 μm in thickness and of μ(1 MHz)=4000, μ(100 MHz)=800 for the insulator‐sandwiched multilayered film of 10 μm are obtained, and these well‐balanced values enable us to apply the materials for high‐frequency recording head.

New crystalline soft magnetic alloy with high saturation magnetization (invited)

Extensive study was made on Fe‐base crystalline alloys in search for new soft magnetic materials with high saturation magnetization by means of sputtering technique. It revealed that newly found FeGaSi and FeAlGe alloy systems possessed excellent soft magnetic properties with remarkably higher saturation magnetization. These new alloy films, annealed in vacuum at 500u2009°C for 1 h, show the magnetic properties of Bs=13 and 15 kG, Hc=0.09 and 0.20 Oe, and μ1 MHz=2000 and 1800 for the FeGaSi and FeAlGe alloy films of 2 μm in thickness, respectively. These values are superior to those of FeAlSi (sendust) alloy which is a typical soft magnetic material with high saturation magnetization. Results of the Co‐added systems of FeCoGaSi and FeCoAlGe alloys are also presented. Discussions are given on various systems of Fe base crystalline alloy films studied, which are classified into four types of groups with respect to magnetic softness.

Stress‐induced anisotropy and permeability of magnetostrictive Co‐based amorphous alloys

Effects of stress‐induced uniaxial anisotropy Ku on initial permeability μ of magnetostrictive Co‐based amorphous alloys were investigated over a wide frequency region by potting ribbons of the material in epoxy resin. Anisotropy in plane caused the low frequency (kHz) permeability to change as μ∝K−l/2u due to domain wall displacements and, therefore, resulted in large eddy current losses due to wall movements which decreased the permeability in the high frequency (MHz) region. Anisotropy normal to the plane caused the low frequency permeability to change as μ∝K−1u due to magnetization rotation and the permeability in the high frequency region took higher values than for the case of in‐planed anisotropy because the eddy current losses were smaller.

High Frequency Permeability Measurement of Magnetic Thin Films

A device for automated measurement of the permeability of thin films is described. Specimens are placed in a high frequency band magnetic field, and the induced emf measured using a differential detection coil, with a damping resistance inserted to prevent resonance. The frequency is varied to find the ¿-f characteristic. The device was used to measure the characteristic of a sputtered Sendust film 4 mm by 4 ¿m up to 100 MHz; measurements required only a few minutes time.

Magnetostriction of transition metal substituted Co-based amorphous alloys

Abstract The effects of the substitutions of 3d-, 4d- and 5d-transition metals for silicon on magnetostriction of Co-based amorphous alloys have been investigated by measuring the tension dependence of anisotropy field in magnetic hysteresis loop. Fractional changes of the magnetostriction with transition metal solutes in Co-based amorphous alloys are qualitatively discussed in terms of the magnetic moment and coordination number, and classified into 3 types, i.e., positive, negative and complicated types, from a viewpoint of the contribution to magnetostriction.

Effects of transition metal substitutions on magnetic properties of Co-based amorphous alloys

Abstract The effects of dilute concentrations of 3d-, 4d-, and 5d-transition metal solutes on magnetic moment and Curie temperature of Co-based amorphous alloys have been investigated. The changes of magnetic properties with transition metal substitutions are similar to those observed for corresponding crystalline Ni-based dilute alloys except thermo-magnetic properties. The effects of transition metal substitutions on magnetic moment in Co-based amorphous alloys are well described in terms of the relative position of the Fermi level and the virtual bound state introduced in the 3d-band of the matrix by the transition metal atoms.

Studies on positive ion behavior in reactive sputtering of yttria-stabilized zirconia (YSZ)

Yttria-stabilized zirconia (YSZ) thin films were deposited by reactive sputtering. Various hysteresis curves, such as those in deposition rate and discharge voltage, were observed as functions of oxygen flow rate: The O2+, Zr+, Y+, YO+, ZrO+, ZrO2+ ions incident on the substrate were analyzed by a quadrupole mass spectrometer (QMS) and their behavior during the course of deposition was observed in detail. It is concluded that the Y/Zr ratio in the metallic film is exactly estimated as the arrival ratio of Y+/Zr+.

Ultrathin Co/Pt and Co/Pd new magneto-optical recording media

Co/Pt and Co/Pd multilayers were prepared by two source dc-magnetron sputtering. Magneto-optical properties of these multilayers were affected by total film thickness, and a perfect squareness of Kerr loop and an enhancement of Kerr rotation angle weresimultaneously achieved when the film thickness was below several hundred angstroms. The improvement of Kerr remanence ratio can be explained by the change in domain structure from a stripe domain to a single domain, d the enhancement of Kerr rotation is due to the optical interference effect with the multiple reflection. The ultrathin films have high corrosion resistance, large Kerr rotation and strong perpendicular magnetic anisotropy even in very thin film thickness. A hermomagnetic writing was successfully made in the magneto-optical disks using these ultrathin media,and the C/N ratio showed 53 dB and 46 dB for Co/Pt and Co/Pd disks,respectively.The figure of merit becomes larger at shorter wavelength, and thus the ultrathin multilayers can be new promising magneto-optical recording media, especially for higher density recording using a shorter wavelength laser.

Density of CoFeTaB amorphous alloys

Abstract Density of Co base Coue5f8Feue5f8Taue5f8B amorphous alloys prepared by the melt quenching technique was measured by pycnometer method. The mean atomic volume of each constituent element estimated from the measured density was found to be independent of concentration of the constituent elements. An empirical relation between the mean atomic volume Vi and atomic radius Ri of the element i was obtained as V i = 1.22 × 4 3 πR i 3 + 1.30 = 4 3 πR i 3 + (1.30 + 0.22 × 4 3 πR i 3 ) for Ta, Co, Fe, Ni and B atoms, with values of Vi estimated from reported density data as well as the present results. A discussion is given on the glass forming maximum concentration for binary metal-metal and metal-metalloid systems using the above relation.