Kim Kong Tham

Approach to High-Density Recording Using CGC Structure

Coupled granular/continuous (CGC) perpendicular media with two different continuous layers, a Co/Pd multilayer and a CoCrPtB cap layer, were compared. It was confirmed that both thickness optimized layers functioned well as exchange coupled continuous layers. A Landau-Lifshitz-Gilbert simulation was performed for various grain boundary thicknesses, and the signal-to-noise ratio improvement predicted by the simulation was in good agreement with experiments. The CGC structure was susceptible to side erasure on account of its Stoner-Wohlfarth type magnetic switching, and the recording performance was dominated by the granular layer. Controlling this behavior would enable further improvement in recording density. The benefits of discrete-track media with the CGC structure are discussed. We found that ion irradiation of the CGC media could be effective to create soft magnetic regions in between recorded tracks, which act as guard bands, improving the recording performance.

Successful fabrication of high Ku columnar CoPt-SiO2 granular film sputtered under high substrate temperature

High substrate temperature sputtered CoPt-SiO2 granular films with columnar grain structure, high perpendicular uniaxial magnetic anisotropy (Ku⊥), and low stacking faults (SFs) are reported. By introducing a CoCr-SiO2 buffer layer onto a Ru layer, SiO2 segregates to Ru grains boundaries and CoCr grains grow epitaxially onto Ru grains. Consequently, the bumpy surface morphology of the underlayer is maintained even though the temperature of the substrate heating is subsequently elevated to around 400 °C. Therefore, the CoPtCr magnetic grains of the CoPtCr-SiO2 granular recording layer can grow epitaxially with columnar structure upon the CoCr grains of the CoCr-SiO2 buffer layer. For deposition of CoPt-SiO2 (no Cr) granular films at the substrate temperature below 400 °C, the increase of SFs can be suppressed such that Ku⊥ can be kept high at around 6.5 × 106 ergs/cm3 (Kugrain of around 9.0 × 106 ergs/cm3, where Kugrain is referred to uniaxial magneto-crystalline anisotropy of the magnetic grains when oxid...

High

Magnetic properties and microstructure of Co₈₀Pt₂₀-30 vol.% (Al₂O₃, TiO₂, WO₃) and Co_82.4Pt_17.6-27.7 vol.% SiO₂ granular films postannealed at various temperatures in a heat-treating furnace were investigated. In this paper, it is found that among these granular films, CoPt-WO₃ granular film shows the highest coercivity (H_c) because of low intergranular exchange coupling of well-isolated magnetic grains. Furthermore, the H_c is enhanced with postannealing because of the increase of the magnetic anisotropy field (H_k^grain) and uniaxial magnetocrystalline anisotropy (K_u^grain) of the columnar growth magnetic grains. The increase of K_u^grain for the postannealed granular film primarily originates from the reduction of the stacking faults as well as the lattice constant ratio.

K_{{{u}}}

The magnetic properties and structures of Co80Pt20–30 vol % oxide (ZrO2, Cr2O3, Y2O3, Al2O3, MnO, TiO2, WO2, SiO2, Mn3O4, WO3, Co3O4, MoO3, and B2O3) granular media deposited at room temperature were investigated. As a result, the following were found. 1) By employing oxides with low melting point temperatures as the granular media, magnetic grains with high saturation magnetization () and perpendicular magnetic anisotropy () are obtained; the increases in and are due to the promotion of the columnar growth of magnetic grains and phase separation or two-phase precipitation between magnetic grains and oxides. 2) The increase in the of the granular media followed by the decrease in the melting point of oxides is due to the reduction in the amount of stacking faults. 3) Among these granular media, the CoPt–B2O3 granular medium has the highest coercivity (H c) and ratio of H c to the magnetic anisotropy field () of 8.0 kOe and 0.4, with and of 1115 emu/cm3 and 1.1 × 107 erg/cm3, respectively. 4) The CoPt–B2O3 granular medium has well-isolated and columnar growth magnetic grains with an average grain size of 6.5 nm.

and Low Intergranular Exchange Coupling of Postannealed CoPt-WO 3 Granular Film

Investigation of surface topography for underlayer with various metal-oxide buffer layer (BL) materials for magnetic recording media is reported. In the previous study, it was found out that the application of a high substrate temperature deposition process to a granular layer with a magnetic alloy and a non-magnetic oxide material, such as CoPtCr-SiO2, will induce lamellar and spherical grains due to the flattening of the underlayer bumpy surface by recrystallization. By depositing a CoCr-SiO2 BL onto the Ru underlayer at room temperature, CoCr grains grow epitaxially onto Ru grains and SiO2 segregates to Ru boundaries. Consequently, bumpy surface morphology of the underlayer is maintained even though heated to around 400 °C before depositing the granular layer. Therefore, CoPt magnetic grains of a Co82.4Pt17.6− 27.7 vol. % SiO2 granular film deposited on the underlayer grow epitaxially on CoCr grains with columnar structure. As a result, high average Ku⊥ of around 6.7 × 106 erg/cm3 can be obtained. Amon...

B2O3: Grain boundary material for high-K u CoPt–oxide granular media with low degree of intergranular exchange coupling

The effect of topological bumpy surface underlayer on compositionally modulated atomic layer stacking in high uniaxial magnetocrystalline anisotropy (Ku) hcp Co80Pt20 film with (00.2) crystallographic texture orientation was investigated. In this paper, the following has been discussed. Concerning preparation of underlayer with various morphologies, an annealing process prior to the deposition of Co80Pt20 film, and introduction of a metal-oxide buffer layer are effective to obtain underlayers with surface roughness ranging from ~0.4 to 2 nm and grain size ranging from ~6.7 to 12.5 nm. To realize a compositionally modulated atomic layer stacking structure, which is confirmed by the high angle annular dark field detector scanning transmission electron microscopy observation, an underlayer with surface roughness less than ~1 nm and/or grain size larger than ~8 nm is required. The compositional modulation shows the same normal direction as substrate normal and the c-axis direction of the hcp grain. To reach Ku of ~1.7 × 107 erg/cm3, surface roughness reduction to ~0.5 nm and grain size increase to ~12 nm are needed.

Metal-oxide buffer layer for maintaining topological bumpy surface underlayer of columnar CoPt-SiO2 granular media deposited at high substrate temperature

The effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media is studied by varying SiO2 content of CoCrPt-SiO2 granular layer. From cross-section and plane-view TEM observation, it can be concluded that each magnetic grain at cap layer (CL) grows on one magnetic grain of granular layer (GL), and inhomogeneous nucleation site at GL leads to inhomogeneous initial growth of continuous layer at CL. This phenomenon leads to the increase of inter granular coupling fluctuation in CL. Evaluation of inter granular coupling between magnetic grains at GL in stacked media with CL deposited directly on GL shows average and fluctuation of exchange coupling constant of around 2.9 erg/cm2 and 0.6 erg/cm2. In order to reduce the inter granular coupling, spacer layer (SL) with Pd material was inserted between GL and CL. As a result, average and fluctuation of exchange coupling constant decrease to 1.4 erg/cm2 and 0.3 erg/cm2 which sugg...

Effect of Topological Bumpy Surface Underlayer on Compositionally Modulated Atomic Layer Stacking in High

Investigation of magnetic properties and microstructure for the Co₈₀Pt₂₀–30vol% B₂O₃ granular medium to clarify the effect of utilizing buffer layer (BL) on intergranular exchange coupling was conducted. It was found that the employment of a Ru₅₀Co₂₅Cr₂₅–30vol% TiO₂ BL with thickness of around 2 nm will avoid physical contact between magnetic grains in the initial growth region, which is effective to intergranular exchange decouple the magnetic grains. On the other hand, for deposition of BL thicker than 2 nm, underlayer will be flatten that brings the possibility of physical contact of magnetic grains and forms a granular film with strong intergranular exchange coupling.

{K}_{u}

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.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.

hcp Co 80 Pt 20 Film With (00.2) Crystallographic Texture Orientation

Recently, closed-packed orientation CoPt-based alloys with oxides granular films have been studied as a candidate for the first generation microwave assisted magnetic recording (MAMR) media. For granular films, it is well known that the CoPt magnetic grains grown on a bumpy surface underlayer have a columnar structure and separated with oxides at the grain boundaries. To increase thermal stability of the grains, the enhancement of uniaxial magneto-crystalline anisotropy (Ku) of the grains is indispensable. In general, to further increase Ku of a CoPt-based alloy grains, increasing the spin-orbital interaction is thought to be effective. One way to achieve this is by forming a compositionally modulated atomic layer stacking structure. In this structure in-plane-disordered atomic layers of each composition are aligned parallelly to the substrate normal. Therefore, the authors consider the realization of such structure on a bumpy surface underlayer will be a big challenge. In this paper, we will discuss about the effect of the bumpy surface including surface roughness and grain size of the underlayer on compositionally modulated atomic layer stacking of overlying Co80Pt20 film in relation with Ku.