Ikuko Takekuma

Reduction in intermediate layer thickness of CoCrPt–SiO2 perpendicular recording media by using Ru–SiO2

A Ru–SiO2 intermediate layer was introduced between the Ru and recording layers to reduce the intermediate layer thickness of CoCrPt–SiO2 perpendicular recording media. A structural analysis revealed that the Ru–SiO2 intermediate layer enhanced the oxide segregation in the initial growth region of the recording layer. A micromagnetic simulation and magnetic property measurements indicated that the Ru–SiO2 intermediate layer reduced the intergranular exchange coupling in the initial growth region of the recording layer without magnetic anisotropy degradation. We reduced the intermediate layer thickness down to 9.1nm by using the Ru–SiO2 intermediate layer while maintaining the signal-to-noise ratio.

Improved Grain Isolation in [Co/Pd]n Multilayer Media for Thermally Assisted Magnetic Recording

The effect of the magnetic and structural properties on recording performance was investigated. Well grain-isolated media were obtained by adding boron and oxygen into the [Co/Pd]n multilayer and cooling the substrate. We found that the recorded bit size could be decreased by reducing the magnetic cluster size. Twenty-flve-nm bits were successfully recorded on the improved media with a magnetic cluster size of about 30 nm.

CoB/Pd multilayers with PtB/Pd/MgO intermediate layers for perpendicular magnetic recording

CoB/Pd multilayer films with a PtB/Pd/MgO intermediate layer were deposited on a soft-magnetic underlayer or on seeded substrates. A TEM analysis revealed that the multilayer films have a well-separated columnar structure just above an MgO layer. This structure may be initiated by the difference in the wetting nature of nonmetallic MgO and metallic Pd, and may be enhanced by the PtB layer. These boundaries were found to act in reducing the exchange coupling, resulting in an improvement in recording performance.

Ultrahigh-Hc granular media with [CoB∕Pt]n multilayer film sputtered under Ar+O2 atmosphere

We developed a [Co∕Pt]n multilayer film for fabricating a perpendicular recording film with an ultrahigh coercivity (Hc). Adding boron into each Co layer and further introducing O2 during deposition yielded a high Hc of 1200kA∕m. Transmission electron microscopy and magnetic measurements suggested that the intergranular exchange coupling was reduced to the level of conventional CoCrPt-oxide granular films. The [CoB∕Pt]n+O multilayer film is applicable to a hard magnetic layer in exchange-coupled composite media as well as energy-assisted magnetic recording media.

High-Resolution TEM Analysis of Perpendicular CoCrPt-SiO

We investigated the relationship among the grain size, the grain boundary width, and the in-plane crystallographic orientation of CoCrPt-SiO2 perpendicular media using high-resolution transmission electron microscope (HR-TEM). The average grain size in a CoCrPt-SiO2 magnetic layer and its dispersion were 7.5 nm and 18%, respectively. The width of the grain boundary was 0.68 nm in average and increased with grain size. In addition, we found a group of neighboring grains with parallel a-axes of h.c.p.-structure, which is defined as a crystal grain cluster. The grain boundary width tended to decrease as the cluster size increased. The results suggested that the size of the crystal grain cluster should be reduced for controlling the intergranular exchange coupling that presumably depends on the grain boundary width.

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FePtAg-SiO2 granular films were fabricated using an in-line sputtering system with a composite alloy target. Two heating methods were investigated in consideration of practical manufacturing processes. Structural analyses showed that the FePtAg-SiO2 film had better L10 ordered structure and clearer grain boundaries when deposited on the preheated substrate than when annealed after deposition. Adding Ag improved both the L10 ordering and the face centered tetragonal (001) texture. Torque magnetometry indicated that the FePtAg-SiO2 film had a uniaxial perpendicular anisotropy of 1.4 × 107 (erg/cc) at an ordering parameter S of 0.72.

Media

We have investigated the role of the Ru underlayer for the segregated structure formation of CoCrPt-SiO2 granular thin film to improve the recording performance of CoCrPt-SiO2 perpendicular magnetic recording media. The coercivity of the granular film decreases with decreasing Ru layer thickness, which comes from the change in the segregated structure. Formation of an oxide grain boundary is needed to obtain higher coercivity. According to a morphology analysis, the Ru layer roughness is closely related to the coercivity. The results indicate that the oxide grain boundary formation of the granular layer is enhanced by the roughness of the Ru underlayer. The shapes of the Ru grains probably serve as a template in CoCrPt grain growth and oxide grain boundary formation. As one of the methods for enhancing the roughness of the Ru underlayer, an island shape growth on the low surface energy materials is applicable. The roughness of the Ru layer was increased using a Pd/MgO/Pd seed layer and high coercivity was successfully obtained even when the Ru layer thickness was 3 nm.

Fabrication of L10-ordered FePt granular media using an in-line sputtering system

L10-ordered FePtAg-C granular media capped with an FePtAg-SiO2 layer were fabricated in order to obtain stable flyability performance on a spin-stand tester. The post-annealed FePtAg-SiO2 was more suitable for the cap layer than an FePt alloy without segregants, since it formed a continuous structure on the well-isolated FePtAg-C layer. By using the optimized post-annealed FePtAg-SiO2 capped medium, the surface roughness (Ra) was reduced to 0.45 nm, thereby enabling stable flying at a glide height of 6 nm.

Role of underlayer for segregated structure formation of CoCrPt-SiO2 granular thin film

Fe-Pt-Ag-SiO2 and Fe-Pt-Ag-C granular recording media with an L10 ordered structure were fabricated using an in-line sputtering system with full-surface alloy targets. To understand the degree of ordering, the x-ray diffraction intensity ratio of a superlattice peak to a fundamental peak was measured for various samples. Some samples showed large intensity ratios despite having low anisotropy energy. This can be explained by the simple theory that the relative intensity at a low diffraction angle increases for samples with weaker preferred orientation. That is, the intensity ratio is affected not only by the degree of ordering but also by the crystalline texture quality. The larger intensity ratio of Fe-Pt-Ag-C media than that of Fe-Pt-Ag-SiO2 media was interpreted as the degraded Fe-Pt(001) texture of Fe-Pt-Ag-C media. Thus, good Fe-Pt(001) texture needs to be achieved without deteriorating the well-isolated granular structure in Fe-Pt-Ag-C media.

Capped L10-ordered FePt granular media with reduced surface roughness

In this study, we investigated an ultra-thin intermediate template layer for use in low noise perpendicular recording media.