Samuel Dacke Harkness

Microstructure and Exchange Coupling of Segregated Oxide Perpendicular Recording Media

The magnetic properties and corresponding microstructure of (Co ₈₀Pt₂₀)_x (metal oxide)_1-x perpendicular recording media have been studied as a function of the volume percentage (vol%) of metal oxide sputtering into the magnetic film. The exchange coupling field (Hex) estimated from the coercivity (H _c) and nucleation field (H_n) decreases rapidly between 0-20 vol% of metal oxide. The analytical transmission electron microscope composition analysis of (Co₈₀Pt₂₀)_x(TiO₂)_1-x media confirms that the microstructure includes crystalline grain cores in an apparently amorphous oxide matrix. The grain cores comprise only Co and Pt in a nearly constant ratio independent of the vol% of oxide addition. The amorphous matrix contains Co, Ti, and O, but no Pt. The Co concentration is nearly constant in grain boundary and core regions, unlike high-temperature longitudinal recording media wherein Co segregates to form a concentration gradient in the grain core. Perpendicular media thus maintain fairly high anisotropy of the grain core phase, even for very high-oxide concentrations that significantly decrease remanant magnetization (Mrt), Hc, and thermal stability (K_uV/kT)

Exchange-coupling effects in perpendicular composite materials

The effect of interlayer thickness on the magnetic properties of exchange-coupled composite media has been studied. Films consisting of a CoPtO hard magnetic layer and a CoCrPt soft layer separated by a Pt interlayer with a thickness varying from 0to40A have been fabricated. At low Pt thicknesses (⩽16A) the exchange coupling forces the layers to switch as a single unit with a reduction in the hard magnetic layer coercivity of >2.5kOe. Thicker Pt layers induce sufficient decoupling to permit each layer to reverse separately. The variation of the coercivity with Pt thickness is complex and suggests that the coupling between the layers is a combination of dipolar and exchange effects.

Influence of oxide on the structural and magnetic properties of CoPt alloy

Perpendicular recording media consisting of isolated CoPt magnetic grains separated with a nonmagnetic oxide grain boundary can be prepared by sputtering a Ru interlayer and then cosputtering CoPt with an oxide material, with low adatom mobility. The oxide material moves into the grain boundaries and isolates the magnetic grains. An increase in the oxide volume fraction in the magnetic layer does not affect the saturation magnetization but significantly reduces the magnetocrystalline anisotropy of magnetic grains. This may impose a limit on the areal density capability of this media design since media with smaller grains will require a larger oxide volume fraction that will reduce magnetocrystalline anisotropy of the CoPt based magnetic grains.

Quantitative measurement of Cr segregation in Co0.8−xCrxPt0.1B0.1 recording media by scatter diagram analysis

We describe the scatter diagram analysis of chemically resolved energy-filtered transmission electron microscopy (EFTEM) images and demonstrate its application in obtaining quantitative information about the segregation of Cr on the nanometer scale. The recording performance of Co–Cr based magnetic media depends critically on the microstructure of the thin film alloy, i.e., the degree of segregation of Cr to the grain boundaries determines the extent of magnetic isolation that can be achieved. Magnetic isolation of the grains reduces transition widths and thereby allows increased recording densities. The EFTEM results obtained correlate well with both the magnetic properties and recording performance of the media; i.e., a higher Cr content of 16 at. % (compared with a 10 at. % sample) shows substantial segregation of Cr with about 8% (0.06%) of the image area, most of it at the grain boundaries, having a Cr concentration which is higher than 24 at. %, and a medium signal to noise ratio of 17.8 dB (15.3 dB).

Different designs and limits of longitudinal magnetic recording media

Combining antiferromagnetically coupled (AFC) and laminated media (LM), we were able to incorporate the stability of AFC media with the signal-to-noise ratio (SNR) of LM. This improvement is directly related to the decrease of the demagnetization field which is calculated to be up to 50% of the LM case for some configurations of AFC+LM that were experimentally realized. The stabilization layer also increases the magnetic energy barrier of the recording layers in the AFC+LM structure, which further improves the stability of this media. An improvement of ∼1 dB in SNR was observed in AFC+LM in comparison to single layer media.

17 Gb/in/sup 2/ areal density demonstration at 214 Mb/s

We have simultaneously demonstrated high areal density and high data rate, in an experiment that closely mimics the operation of disc drive products. The system involves thin-film media, GMR merged heads, broad bandwidth electronics, and an EPR4 channel with post-processing. The results presented reflect a statistical sample of components, rather than one-of-a-kind devices. In order to determine the areal density accomplished, we demanded that the bit error rate performance be insensitive to significant deviations of the head position from the recorded track center. We present a thorough description of the components and the SNR budget. The areal density accomplished varies between 15.1 Gb/in/sup 2/ at 193 Mb/s, and 17.1 Gb/in/sup 2/ at 214 Mb/s. A series of areal density capability assessments was obtained by applying various margin conditions. This was done to demonstrate robust experimental results. The outcome of this work may be applied to product development.

23.8 Gb/in.2 areal density demonstration

We have demonstrated 23.8 Gb/in.2 areal density using a merged read-write grant magnetoresistive head, with an oriented thin film medium tested with broadband electronics and enhanced EPR4 channels. The medium had high signal to noise ratio metrics that was robust unto temperatures as high as 75 °C. A unique aspect of the head design at such a narrow track width is the simultaneous enhancement of the transducer sensitivity while keeping product and system manufacturability in the forefront. The areal density was demonstrated at a track density of 45.8 k tracks/in., using photolithographically defined poles and linear density of 520 k bits/in.

Crystallographic stacking faults in antiferromagnetically coupled media

Synchrotron x-ray scattering has been used to examine stacking faults in the constituent layers of an antiferromagnetically coupled (AFC) media film. By varying the x-ray incident angle, we have varied the x-ray penetration depth and, hence, the layer under examination. Three films were studied, one consisting of a full AFC media structure and the other two consisting of a single magnetic layer with the thicknesses of the constituent layers in the AFC medium. The stacking faults in the bottom magnetic layer were investigated using the single layer film. The stacking fault density in the top AFC media layer was measured using careful depth profiling to ensure that the penetration depth of the x rays remained within the top layer. We were unable to estimate the stacking faults in the bottom layer film but the stacking fault densities are constant at approximately 5% for the top layer of the AFC media and the top layer single film within a relatively large error of 3%.

Effect of Ru interlayer on the crystallographic texture of AFC media

In this paper explained about the effect of the Ru interlayer on the quality of the crystallographic texture of the top magnetic layer in a series of AFC by comparing them to conventional single layer disks.

Recording performance enhancement via in-situ annealing of multilayer media structures

A novel technique for incorporating rapid thermal annealing into media sputter fabrication has facilitated the production of flyable media samples. Discs are fabricated with standard processing techniques to control physical grain size and crystallite texture. A CrMn caplayer ranging in thickness between 0.5 and 5 nm is subsequently deposited to provide the Mn-diffusant necessary to achieve post-treatment exchange decoupling. While still in-situ and before application of protective overcoats, the discs are exposed to temperatures between 200/spl deg/C and 350/spl deg/C compatible with most media production processes. A threefold increase in coercive force (peak reaching /spl sim/3800 Oe) and 10 dB improvement in medium signal-to-noise ratio is observed for the optimized process.