Hiroaki Nemoto

NEW RECORDING METHOD COMBINING THERMO-MAGNETIC WRITING AND FLUX DETECTION

We have developed a new perpendicular thermo-magnetic recording method coupled with magnetic flux detection. The resolution is substantially improved by flux detection. Compared to the latest magneto-optical disk drives, the carrier-to-noise ratio of a reproduced signal is 5 dB higher, and the recording density reaches 8.3 Gbit/inch2. Moreover, this recording method has a good affinity to near-field optics, and it is an effective technique for attaining a higher density beyond the super-paramagnetic limitation in longitudinal magnetic recording.

Thermally assisted magnetic recording on flux-detectable RE-TM media

We studied a thermally assisted magnetic recording on flux-detectable RE-TM media. This recording scheme has a close affinity with near-field optics such as solid immersion lens (SIL) optics and scanning near-field optical microscope (SNOM)-type optics. The requirements for high-density thermo-magnetic recording and a novel near-field optical head were discussed.

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.

Exchange-Coupled Magnetic Bilayer Media for Thermomagnetic Writing and Flux Detection

We have newly developed a perpendicular thermomagnetic recording coupled with magnetic flux detection. Conventional magneto-optical thin films with TbFeCo compensation compositions are advantageous for thermomagnetic writing, but insufficient for magnetic flux detection due to low flux density at room temperature. We therefore designed magnetically exchange-coupled bilayer media suitable for flux detection by adding a magnetic layer with high flux density to a conventional TbFeCo magnetic recording layer.

Dual Segregant Perpendicular Recording Media With Graded Properties

We have introduced structural and magnetic gradations into the granular layer in capped media to promote incoherent switching and hence reduce the contribution of the cap layer to writeability improvement. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the granular layer was composed of two different microstructures: a well-isolated structure with Si-oxide and Cr-oxide at the bottom portion and a less isolated structure with Si-oxide at the top portion. We found that the graded media exhibit better adjacent track interference (ATI) performance than the conventional media in similar overwrite, magnetic core width, and bit error rate conditions. The graded media have shallower angular dependence of remanent coercivity while maintaining small magnetic cluster size, which is probably the main reason for the improved ATI performance.

Analysis of interfacial magnetic anisotropy in Co/Pt and Co/Pd multilayer films

Analysis of Co∕Pt and Co∕Pd multilayer films was performed to investigate the dependence of interfacial magnetic anisotropy (IMA) and induced magnetization on the thickness of the laminated Pd or Pt layers. For the Co∕Pd films, the IMA energy increased as the thickness of the laminated Pd layer was increased up to ∼0.8nm and depended proportionally on the amount of the induced magnetization. This suggests that the whole magnetic moment induced in a few Pd atomic layers contributed to the IMA. In contrast, for the Co∕Pt films, this proportional relationship only held when the thickness of the Pt layer was less than ∼0.2nm. Since one Pt monolayer is 0.225nm thick, the amount of the IMA energy in the Co∕Pt films is proportional to the number of Pt–Co atomic contacts. This difference between Co∕Pt and Co∕Pd multilayer films is attributed to the difference in the latent ferromagnetism between Pt and Pd.

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.

Dependence of Co/Pd superlattice properties on Pd layer thickness

Palladium (Pd) layers in contact with Co layers can be magnetically polarized. By examining the thickness dependence of this magnetization, we determined the induced magnetization distribution in Pd layers in sputtered Co/Pd superlattice films. The perpendicular anisotropy energy was strongly related to the induced magnetization, which was considerably sensitive to the sputtering conditions, particularly the deposition rate and Ar pressure.

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.

Incoherent Switching Amount Analysis of Exchange Spring Media by Using Initial Minor Loop Slope Measurement

We describe a newly developed initial minor loop slope (IMLS) experimental method capable of measuring reversal switching in exchange spring perpendicular media. The slope peak height is centered near the mediums coercivity Hc. The magnitude of the peak signal is correlated with the soft top (cap) layers moment, Mst, and the exchange coupling strength between the cap and hard magnetic oxide layers. The peak position was correlated to the media Hc for media that is thermally stable and migrates to smaller fields in less stable media. The IMLS results are compared with both remanent angular dependence coercivity, Hcr, measurements and micro-magnetic simulations. This technique provides a simple method of characterizing incoherent switching behavior in different types of exchange spring media.