A simplified exchange coupled composite (ECC) dot structure with a reduced switching field and small applied field angle dependence in the switching field is proposed. It was found from a spin model analysis that a reduced switching field as well as a small applied field angle dependence of the field is obtainable even for two-layer ECC dot when the anisotropy axis is weakly inclined with an increased anisotropy for the soft layer. The switching properties of the two-layer ECC dots were confirmed using a micromagnetic simulation. A minimum normalized switching field of 0.51 was obtained for a two-layer ECC dot model of stacked cubes with a size of 5 nm and an anisotropy inclination angle of 10°. Recording simulation on a bit-pattered medium of the two-layer ECC dot array suggested the possibility of a high areal density recording beyond 4 Tdot/in2 by shingled recording. It was also confirmed by simulation that the proposed inclined anisotropy ECC dot could be applicable to granular media for narrow track recoding.

Dot arrays of Co-Pt with a dot density of 1 Tdot/in2 were fabricated using electron beam writing. Low-energy ion etching was used to prevent the dots from deteriorating the magnetic properties. We found from the magnetic properties measured using x-ray magnetic circular dichroism that etching with low-energy ions not only caused little damage to the magnetization but also that the anisotropy field of the dots resulted in high coercivity. These results demonstrate the effectiveness of etching with low-energy ions to achieve bit-patterned media with an areal density of 1 Tbit/in2. Furthermore, the magnetic dot array with a dot period of 25 and 30 nm was fabricated by electron beam writing and etching with low-energy ion. Coercivity of these dot arrays was found to be more than 5kOe.

Exchange coupled composite media Co–TiO2/Pt/CoPt–TiO2 were studied in terms of structures and magnetic properties. In these media exchange coupled grains with soft-grain/interlayer/hard-grain structure are successfully formed although the Pt interlayers were undoped. Based on that ECC structure, Co–TiO2 soft layers with higher saturation magnetization were found to be more useful to reduce the interlayer thickness for the optimal exchange coupling state and also the total thickness of the medium. Meanwhile, the sensitivity of coercivity on the interlayer thickness can also be decreased. On the other hand, the Pt interlayer induced interface anisotropy and strengthend intergranular exchange coupling; therefore, improved coercivities (Pt thickness less than 0.5 nm) and thermal stability were observed.

Field calculation with a finite-element method was performed for optimization of the shielded planar head composed of a tapered pole in both down and cross track directions and a wrap-around shield. Especially, effect of the taper angle of the main pole and the gap length and the height of the shield on head field was investigated to obtain a strong head field with a sharp distribution. In order to explore potential of the planar head, comparison with a conventional head with a normal main pole with a short throat was made and feasibility of 1Tbit/in2 recording with patterned media was discussed in terms of magnetization reversals of aimed track and thermal stability of magnetization on adjacent tracks.

We developed a micro-magnetometry with a 2.5μm spatial resolution based on micro X-ray magnetic circular dichroism (XMCD) technique in order to study magnetic properties of dot arrays for bit-patterned media. This micro-magnetometer was applied to the magnetic characterization of Co–Pt dot arrays fabricated by ion beam etching. As the dot size became small, the intensity of XMCD drastically decreased for dots fabricated by Ga-focused ion beam. This suggested that the dot edges were damaged magnetically by implantation of Ga ions. The damaged width of the dot edge was estimated to be about 13nm from the decrease in XMCD intensities. This damaged edge width agreed with the ion-implanted area estimated by Monte-Carlo simulation. The less-damaged effect of Ar ion etching was verified by the XMCD measurement of Co–Pt dots with diameter of 20 and 70nm. It was concluded that ions with inertness, lower energy and smaller atomic number should be used to fabricate dot arrays with an areal density of 1Tbit/in2.

An in-field magnetic force microscopy (MFM) observation technology was introduced to study media noise in perpendicular recording medium. Magnetization reversal field (HR) distribution of the recording medium could be mapped by this technology. We have extracted media noise signal image from recording pattern. The noise signal image was converted to a contour image, in which peak areas represented high-noise areas. To clarify the relationship between HR distribution and the media noise, we novelly combined the contour with the HR-map. The results show that the media noise mostly gets generated in the lower-HR areas, which indicates the lower-HR area is one of the important origins of the media noise. For comparison, a simulation work was also performed by introducing a model based on experimental parameters. The simulation agreed with experimental results very well.

Magnetic properties of soft/hard stacked perpendicular magnetic recording media were investigated using a two-moment model with taking account of demagnetizing energy. Demagnetizing energy of the soft layer may improve the uniformity of magnetic properties of the composite media and also decrease the interlayer thickness, although weaken the thermal stability a little. The application of high saturation magnetization (Ms) soft magnetic material as the soft layer may compensate for the undesirable contribution while maintaining its benefits.

A new type of oxide composite film was proposed as perpendicular magnetic recording medium. The storage layer is composed of Co-Pt and Ti-oxide. By transmission electron microscopy (TEM) observation, the film exhibited a well isolated fine granular structure with small and uniform Co-Pt grains surrounded by TiO/sub 2/. More sufficient segregation by TiO/sub 2/ was realized from the beginning of the layer growth compared with other oxide addition film, resulting in a magnetically weak coupled structure. This film has a relatively large magnetic anisotropy constant (K/sub u/) and saturation magnetization (M/sub s/) of more than 5/spl times/10/sup 6/ erg/cm/sup 3/ and about 800 emu/cm/sup 3/, respectively. The structure was brought about by a high sputtering gas pressure of Co-Pt-TiO/sub 2/ film deposition.

Ultra-thin Fe-Pt films of perpendicular composite media were studied, It was found that a preparation condition at a temperature of 375 degrees C and introduction of an exchange-decoupling layer between the Fe-Pt layer and the soft-magnetic underlayer led to reduction of the initial growth layer of the Fe-Pt film. A 5 nm thick Fe-Pt medium exhibited a high SNR and a high recording resolution with high thermal stability.

Co–Pt–Ta2O5 film was investigated for perpendicular magnetic recording media. Perpendicular coercivity of over 3kOe was obtained when the film was deposited at high Ar gas pressure of 7Pa, where Ta existed in a state of metal–oxide mixture in the film. It was indicated that grain isolation was obtained in the film. On the other hand, no increase in the coercivity was obtained by deposition introducing oxygen gas into Ar gas, although a fraction of oxidized Ta increased.

In this report, we propose a new oxide added granular medium with a Co-Pt film which exhibits developed magnetic decoupling. The film was sputter-deposited on glass disks at room temperature and its magnetic properties such as magnetic anisotropy and coercivity were measured with a Kerr effect magnetometer. Film thickness of the storage layers was fixed at 15 nm. Compositional analysis was carried out by an Auger electron spectroscopy.

The increase in nonlinear transition shift (NLTS) for double-layered perpendicular magnetic recording media with increased M–H loop slopes was studied using micromagnetic simulation. The simulation indicated increased NLTS for the media, but NLTS was reduced for a medium with a higher coercivity. It was concluded that increased NLTS of the media is mainly caused by the decreased write head field gradient corresponding to the decreased write field due to the increased recording sensitivity of the media. It was indicated that use of media with a higher coercivity could reduce NLTS, and an increased write head field gradient directly reduces NLTS of the media.

Preparation conditions of Co–Pt–Cr–SiO2 granular type films for perpendicular recording media were studied. Crystal orientation of the Co–Pt–Cr–SiO2 film directly depended on that of the Ru underlayer. Films with smaller grain size and grain size distribution tended to exhibit higher perpendicular coercivities. The Ar pressure during sputtering of Co–Pt–Cr–SiO2 films and Ru underlayers was found to be an important factor for controlling the surface morphology. A Ta pre-coat layer could improve the crystal orientation of the Ru underlayer and the surface smoothness so that it increased the coercivity of the Co–Pt–Cr–SiO2 films.

A Co–Pt film with large magnetic anisotropy at room temperature deposition was studied in terms of magnetic and structural properties. A high Ar gas pressure deposition of the Co–Pt film with a high crystal orientation could realize excellent magnetic properties such as a high perpendicular coercivity and a large magnetic anisotropy. This deposition technique of the Co–Pt film could form physically isolated and magnetically weak coupled grains. Magnetization reversal mechanism of the Co–Pt film deposited at a high Ar gas pressure was revealed to be a rotational mode, while the Co–Pt film deposited at low gas pressure seemed to be a magnetic domain wall motion.

In this report, the new head structure and its writing performance are discussed based on fabricated real single-pole heads.

The effect of oxygen on magnetic properties of Co–Pt–Cr–SiO2 films deposited with various sputtering conditions of Ar gas pressure and deposition speed was investigated. It was suggested that optimum oxygen composition in the film for obtaining large Hc was to have the oxygen/silicon ratio of 2 in Co–Pt–Cr–Si–O films. No X-ray photoelectron spectroscopy spectrum of Co–O or Cr–O was observed in this film, while the Si spectrum shifted to higher energy indicating Si–O bonding. The film exhibited a well-isolated fine grain structure, and the oxygen/silicon ratio was almost constant throughout the depth. It is suggested that the granular structure with SiO2 grain boundaries is formed from the initial deposition stage.

In perpendicular magnetic recording, improvement of recording resolution of single-pole (SPT) head is considered to be one of the future subjects. In a cusp-field single-pole (CF-SPT) head, it is useful to narrow the trailing gap for improving the recording resolution and also overwrite performance. Furthermore, the CF-SPT head, which has double return-yokes on both sides of the main-pole, is expected to show excellent writability even with a thin soft underlayer (SUL). It is experimentally confirmed that the head with double return-yokes shows high writability combined with a thin SUL medium compared to a head with a single return-yoke. It is concluded that the CF-SPT head with a narrow trailing gap shows a high recording resolution together with a high writability so as to allow the use of a thin SUL productively.

In the overwrite process, overwrite noise is caused by both incomplete erasure of the old magnetization data (non-saturated overwrite recording) and the modulation of the write magnetic field by the old magnetization. The overwrite modulation of the post-recording signal is caused by easy/hard transition shifts on the pre-recorded signal. From theoretical analysis, it was indicated that the frequency components generated from easy/hard transitions appear only around the even harmonics of the post-recording signal as the sideband having odd harmonics of the pre-recorded signal, while non-saturated overwrite spectrum is characterized by the sideband around the odd harmonics of the post-recording signal. The dominant source of overwrite noise was experimentally distinguished by the locations of the frequency components of the reproduced overwriting signal. The change from non-saturated overwrite to a modulated one was observed with increasing the overwrite head current.