Y. Iwasaki

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=450 °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.

Soft magnetic properties of FeRuGaSi alloy films: SOFMAX®

To advance new soft magnetic materials of an FeGaSi alloy into the commercial world, improvements on various properties were designed by introducing additive elements without sacrificing its high saturation magnetic induction. The detailed studies on the diversified properties, such as saturation magnetic induction, film internal stress, wear resistivity, and so on, were performed. High‐frequency permeability of the laminated structure film was also investigated. As a result, the Ru‐added FeRuGaSi alloy films, whose typical compositions are Fe72Ru4Ga7Si17 and Fe68Ru8Ga7Si17 (at. %), prove to be excellent soft magnetic materials especially appropriate for the magnetic recording/playback head core use.

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 500 °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.

Fabricating nanoscale magnetic mounds using a scanning probe microscope

Nanometer‐scale mounds were fabricated by applying voltage pulses between a substrate and an atomic force microscope cantilever coated with magnetic material. Mounds were formed on both insulator and conducting substrates. Magnetic force microscopy (MFM) observations of the fabricated mounds were performed, and the contrast was turned over by reversing the magnetization of the tip, which is convincing proof that the mounds are magnetic. The MFM images also suggest that the mounds are perpendicularly magnetized. These results demonstrate that scanning probe microscope based nanofabrication is a promising method to fabricate nanoscale magnetic dots on any kind of substrates.

Magnetoresistance of Co-X/Cu (X = Fe, Ni) multilayers

Abstract We report the magnetoresistance (MR) of Co-X/Cu (X = Fe, Ni) multilayers prepared by dc magnetron sputtering. The maximum MR ratio was obtained with Co/Cu. The MR ratio of Co-Ni/Cu decreased monotonically with increasing Ni content, while that of Co-Fe/Cu decreased rapidly at the fcc-bcc crystal phase transition point.

Electron microscopy on Co–CoO obliquely evaporated magnetic tapes

Abstract Microstructures of Co–CoO obliquely evaporated tapes were studied by transmission electron microscopy with an energy filter. The structures were the following. The columnar structure consisted of Co-rich regions enclosed by O-rich regions. CoO crystallites were densely packed between Co-rich columns where they had been considered “interstices”. The columnar structure of single layered film was different from that of double layered film.

Nanoscale magnetic mounds fabricated using a scanning probe microscope

Fe, Co, Ni or CoCr mounds of several tens of nanometer scale were fabricated using a scanning probe microscope. Mounds were formed on both insulator and metal substrates. MFM observation of the fabricated mounds were performed, and the contrast was turned over by reversing the magnetization of the tip, which is a convincing proof that the mounds are really magnetic. The magnetic structure inside the Co mound is supposed to be multi-domain, from a semi-quantitative analysis of the magnetic interaction between the mound and the MFM probe.

Soft magnetic properties of crystalline high Bs Fe-Co-Si and Fe-Co-Si-Al sputtered films

Soft magnetic properties of crystalline Fe-Co-Si and Fe-Co-Si-Al sputtered films have been investigated. Fe-Co-Si alloy films show high saturation flux density up to 14 kG with low coercivity of 0.7 Oe around the narrow composition range of Co 11 to 13 at.% and Si 20 to 22 at.%. In Fe-Si-Al the composition with soft magnetism was restricted around the Sendust composition. Fe-Co-Si-Al films which are solid solution of Fe-Co-Si and Fe-Si-Al show high saturation flux density of 12 to 14 kG with low coercive force of about 0.5 Oe. The soft magnetic characteristics in Fe-Co-Si-Al alloy films were comparable to Sendust film. These results suggest the existence of a composition region which possesses both zero-magnetostriction and zero-magnetocrystalline anisotropy constant in Fe-Co-Si and Fe-Co-Si-Al alloy films.

A new apparatus for measuring thermal expansion of thin films

An apparatus for measuring the thermal expansion of thin films has been developed. The film, deposited on a substrate, was heated with hot nitrogen gas and the warp of the substrate was measured by an optical lever method. Films of iron, chromium, vanadium, and cobalt ferrite were deposited by sputtering and their thermal expansions were measured between 25 degrees C and 100 degrees C. The values of the thermal expansion coefficients were in good agreement with reported data for the bulk specimens.

Observation of Magnetization Transition of a Co-CoO Obliquely Evaporated Magnetic Recording Tape

Magnetization transition of a magnetic recording tape can be well understood when the magnetization distribution is precisely estimated. This paper visualizes the magnetic flux distribution in the cross-sectional plane both inside and outside of a tape in the as-recorded state by electron holography. The recorded images are then compared with computer simulation images.