COPTB(O) ALLOY-FILMS AS NEW PERPENDICULAR RECORDING MEDIA

In search of new hard magnetic materials with high saturation magnetization and large coercivity, a comprehensive study was made on numerous Co- and CoPt-base crystalline alloys by means of sputtering techniques. It revealed that a newly found CoPtB(O) alloy system possessed excellent hard magnetic properties with remarkably large perpendicular coercivity and high saturation magnetization. This new alloy film, deposited onto room temperature substrates, shows the magnetic properties of 4πMs=12 kG, H ⊥c=4000 Oe, and perpendicular anisotropy field H k=22 kOe. These values are superior to those of prevailing materials such as CoCr perpendicular and CoPt or CoNi longitudinal recording media. The typical composition is Co69Pt20B6O5 (at. %), and oxygen plays a momentous role on the coercivity in this alloy film. As a magnetic recording medium, a write/read experiment of this film shows that the readout signal has a +9 dB peak-to-peak amplitude compared with that of metal particle tape at 1 μm wavelength and has +10 dB compared with that of a CoCr perpendicular medium at 0.5 μm wavelength.