Abstract
Investigation of magnetic properties and microstructure of granular media with various multiple oxides as the grain boundary material is reported. Saturation magnetization (Ms), uniaxial magnetocrystalline anisotropy (Ku), and magnetic grain diameter (GD) of the granular media show linear correlation with volume weighted average for melting point (Tm) of each oxides (Tmave). Ku of magnetic grains (Kugrain) shows a trade-off relation with GD that it is a big challenge to satisfy both high Kugrain and small GD by only controlling Tmave. To obtain a granular medium with appropriate Kugrain, GD, and low degree of intergranular exchange coupling, the combination of Tmave control of grain boundary material by mixing oxides and employment of a buffer layer are required. Here the degree of intergranular exchange coupling is estimated from the slope of M-H loop at around coercivity (α). By applying this technique, a typical granular medium with Kugrain of 1.0×107 erg/cm3, GD of 5.1 nm, and α of 1.2 is realized.
Highlights
Since the first hard disk drive with perpendicular magnetic recording was launched into the market, CoPt-oxide granular media have been utilized for the recording media
We have found that the application of oxide with low melting point (T m): B2O3, is effective to obtain columnar growth grains with high Ku and magnetic properties of the granular media with single oxide have linear relationship with T m of the oxide.[8,9]
It is shown that the introduction of a buffer layer (BL) underneath the granular media has a great impact on promoting the intergranular exchange decoupling of the media.[11]
Summary
Reduction of intergranular exchange coupling and grain size for high K u CoPt-based granular media: Metal-oxide buffer layer and multiple oxide boundary materials. Investigation of magnetic properties and microstructure of granular media with various multiple oxides as the grain boundary material is reported. Saturation magnetization (Ms), uniaxial magnetocrystalline anisotropy (Ku), and magnetic grain diameter (GD) of the granular media show linear correlation with volume weighted average for melting point (T m) of each oxides
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