K.E. Johnson

Role of oxygen incorporation in Co-Cr-Pt-Si-O perpendicular magnetic recording media

The effect of oxygen incorporation on the crystallographic, magnetic, and recording performance of perpendicular magnetic recording (PMR) oxide media was investigated. The media were prepared by dc-magnetron sputtering of CoCrPt-SiO/sub 2/ targets in an Ar/O/sub 2/ gas mixture. X-ray photoelectron spectroscopy (XPS) detected Cr-O peaks in the sputtered film, whereas no strong evidence of SiO/sub 2/ is seen. Moderate oxygen incorporation in the film (/spl sim/15 at%) promotes Cr-O formation in the grain boundary and results in a dramatic increase of coercivity H/sub c/ and signal-to-noise ratio (SNR). However, as the O/sub 2/ content is further increased, oxide incorporates into the core of the grains, resulting in decreased H/sub c/, magnetization and SNR.

Anti-parallel coupled soft under layers for high-density perpendicular recording

A promising soft magnetic under layer (SUL) structure consisting of anti-parallel coupled soft layers (APS) is investigated to improve the performance of high-density perpendicular recording media. CoCrPt-O recording media with average grain diameter /spl sim/6 nm, coercivity of 5 kOe and nucleation field of -2 kOe is fabricated on both conventional SUL and APS. Wide-area adjacent track erasure (ATE) is observed for conventional SUL, which increases at lower interlayer spacing (t/sub IL/). APS structure enables the suppression of ATE even up to t/sub IL/=10 nm. Moreover, APS leads to reduced dc erase noise and improved signal to noise ratio particularly for SUL thicknesses <100 nm.

Magnetic materials and structures for thin-film recording media (invited)

There have been three distinct stages in the development of magnetic materials and processes for thin-film media. The first era focused on designs for use with inductive heads. Vacuum sputter deposition techniques were developed to achieve high Hc, with high Ms materials epitaxially grown on Cr underlayers. The second phase of thin-film media development demanded media optimized for the use with MR heads. Noise reduction through the decoupling of grains by chemical segregation of Cr at the grain boundaries proved effective. The introduction of giant magnetoresistance heads required low noise and high Hc but added the necessity of the reduction in the average grain size and grain size distribution width. The next and perhaps final phase of thin-film media development will be focused on the minimization of the magnetization thermal decay by the use of materials and designs that produce high KuV/kBT ratios.

Seedlayer and pre-heatfng effects on crystallography and recording performance of CoCrPtB perpendicular media

Summary form only given. Perpendicular magnetic recording (PMR) media has been considered as a promising candidate in order to achieve over 100 Gbir/in2 recording density. However, thermal stability at low recording densities has been a concern especially for low-noise PMR media. Achieving high perpendicular HC and unity squareness (SQ=Mr/Ms) is necessary to improve thermal stability and has been proposed by using either high substrate temperature or post annealing in CoCr based alloy. However, the influence of high heating on recording performance deserves further investigation. In this work, we studied on the seedlayer and heating effects on the crystallographic, magnetic and recording properties of CoCr18Pt16B4 granular PMR media. The CoCrPtB films were sputtered on preheated glass substrates with a Ru underlayer (UL) or a Ta/Ru UL on top of a 300-nm-thick NiFe17Mo4 soft magnetic underlayer. We report that Ta/Ru UL developed in this study greatly enhances Ru(0002)/Co(0002) crystallography, HC, SQ and thermal stability without degrading media signal-to-noise ratio (So/Nm).

Recording characteristics and thermal stability comparisons between antiferromagnetically coupled and conventional media (invited)

We report on the recording performance and thermal stability of antiferromagnetically coupled (AFC) media with varying top and bottom layer thickness as compared with those of highly oriented conventional longitudinal recording media. AFC media offers the expected merit of low Mrt designs such as narrow pulse width (PW50), while maintaining good thermal stability. However, the magnetostatic field resulting from thicker total magnetic thickness in AFC media results in poor overwrite (OW) and a degradation in nonlinear transition shifts (NLTS). Thermal stability of AFC media is mainly determined by intrinsic coercivity of the top layer plus the AF exchange field and the magnetostatic field acting on the top layer through a Ru layer. Low noise conventional media with high orientation ratio (OR) can be produced with an acceptable thermal decay equivalent to AFC media at Mrt values above 0.25 memu/cm2.

Highly in-plane oriented CoCrPtB longitudinal media for 130-Gb/in/sup 2/ recording

A recording density of 130 Gb/in/sup 2/ was achieved using thermally stable conventional CoCrPtB longitudinal media. The high in-plane orientation ratio (OR) of the media resulted in an excellent recording performance due to a narrow switching field distribution as well as a high thermal stability caused by narrow energy barrier distribution. The low noise is attributed to the fully isolated fine grains with a narrow size distribution. A good in-plane c axis crystallographic texture was achieved by using an optimum multilayered structure of underlayer and magnetic layers. A detailed study of high OR media is reported by characterizing the magnetic, microstructural, and read/write properties.

Seedlayer and underlayer effects on the crystallographic orientation and magnetic recording performance of glass media

Seedlayer and underlayer effects on crystallographic orientation and recording performance were studied for CoCrPtB media sputtered on glass substrates. For this study, the seedlayers are XAl (X=Ni, Co, Ti, and Ru) and the underlayers are CrY (Y=V, Mo, W, and Ti). It was found that not only different seedlayers, but also different combinations of seedlayer and underlayer, led to different magnetic performance. NiAl and CoAl seedlayers orient the Co c axis to (10.0) and TiAl and RuAl seedlayers produce (11.0) Co orientation. For the NiAl and CoAl seedlayer, CrV and CrW underlayers develop less out-of-plane c-axis orientation and higher coercivity and coercive squareness while CrTi and CrMo underlayers work better for TiAl and RuAl seedlayers, respectively. Media with RuAl seedlayers have better parametric performance than media with NiAl and CoAl seedlayers. The detailed relationship between seedlayer and underlayer types and crystal orientation and recording performance is discussed.

Systematic study of in-plane magnetic anisotropy in CoCrPtB/Cr media

Circumferential texturing in longitudinal recording media induces in-plane magnetic anisotropy. It is characterized by orientation ratio (OR), which is an important parameter affecting media performance. Our work shows that among the media with different OR values (including isotropic media with OR=1), the ones with higher OR have both better thermal stability and better recording performance. Therefore, it is important to have a better understanding of the mechanism for in-plane anisotropy so that OR can be further increased. Several mechanisms for in-plane anisotropy have been proposed through micromagnetic analysis or empirical methods. A systematic study of OR in CoCrPtB/Cr media was performed to explore the mechanism of in-plane magnetic anisotropy. Circumferential texture roughness has the most effect on OR, but OR is also strongly affected by magnetic alloy composition and sputtering process parameters such as substrate temperature, underlayer thickness, and magnetic-layer thickness. Higher substrate temperature, thinner underlayer thickness, and thinner magnetic-layer thickness all lead to higher OR. These results suggest that the in-plane magnetic anisotropy comes from stress anisotropy via the inverse magnetostrictioneffect. The stress is induced at the magnetic-layer/underlayer and underlayer/substrate interfaces, while the anisotropy is suggested to arise from the topology of the circumferential texture lines.

Transition and DC noise characteristics of longitudinal oriented media

Transition and DC noise characteristics of longitudinal recording media were studied as a function of orientation ratio (OR). With increasing OR, a substantial decrease of DC noise is observed against the gradually increasing transition noise, resulting in the reduced media total noise. The increase in the media transition noise with OR is attributed to the increase in the cross-track correlation length s. The experimentally estimated s for the media with OR=1.8 is significantly larger than that of the media with OR=1.25, possibly resulting from the difference in magnetostatically coupled Co grains aligned to the track direction. For high-density low M/sub r/t designs, reducing DC noise by increasing OR, in spite of an increase in transition noise, becomes an effective means to increasing areal density.

Ultrathin carbon overcoats: processing, characterization and tribological performance

The thickness of carbon overcoats has been reduced to 30 /spl Aring/ or less to achieve high areal density in magnetic media. Presently, technologies such as ion beam deposition and plasma enhanced chemical vapor deposition (PECVD) produce thin carbon overcoats with a high fraction of sp/sup 3/ bonding. These hard and dense overcoats exhibit good wear durability and corrosion resistance. This paper discusses processing, characterization, and tribological and corrosion performance of ultrathin overcoats (30 /spl Aring/ or less) produced by PECVD. The physical and chemical properties of the carbon overcoat affect the carbon-lubricant bonding, which subsequently determines the head-disk interaction. Since optimal properties of the carbon vary at the lubricant and magnetic layer interfaces, an interfacial functionality approach is needed for the design of thin overcoats. Functionalized carbon overcoat is a design that consists of a PECVD carbon layer with a sputtered functional layer on top. Characterization and tribological performance and comparison of functionalized carbon overcoat with PECVD carbon is also presented.