Brij B. Lal

A new series of quaternary Co-alloys for high density rigid-disk applications

Quaternary media CoCrPtTa(Q) with Hc up to 2400 Oe and Mrt greater than 1.3 memu/cm/sup 2/ have been investigated for longitudinal magnetic recording. Magnetic properties and microstructure of the films were compared with CoCrTa(T) media. The coercivity decreases monotonically with temperature, and the magnetization has a very small dependence on temperature. The differential remanence measurements of Q and T media indicate fairly strong interactions among the crystallites. The Q media with 5-10% Pt exhibit 25-75% higher coercivity than the ternary media T with same atomic percentage of Cr and Ta. The media Q, containing 9.5% less Co produce the same remanence magnetization and slightly higher signal amplitudes. X-ray diffraction and transmission electron microscopy (TEM) data show larger grain-size and more grains with c-axis in-plane orientation in the Q media which can account for the higher coercivity. >

Preferred orientation in Cr‐ and Co‐based thin films and its effects on the read/write performance of the media

This work investigates the formation of preferred crystallographic orientation (PO) in Cr underlayer as well as CoCrTa and CoCrPtTa thin films and its effects on the recording performance of longitudinal media. The results show that the thin‐film media with comparable coercivity but different crystalline PO as measured by x‐ray diffraction exhibit significant difference in high‐frequency signal amplitude, pulse width, and signal‐to‐noise ratio. To illustrate the effect of PO on parametric performance, CoCrTa/Cr and CoCrPtTa/Cr media were sputtered on different substrates and/or using special sputtering processes to achieve comparable coercivity but different PO in the films. A PO of Cr(200), which normally occurs on the NiP/Al substrates under adequate sputtering conditions, is found to be the key to obtaining a PO of Co(11.0) in Co‐alloy media. The consequence of preferred in‐plane c‐axis orientation is a higher coercivity and better parametric performance of the medium. The formation of PO in the Cr und...

Grain size analysis of longitudinal thin film media

Magnetic layer grain size plays an important role in determining the materials properties of longitudinal magnetic thin film media. Therefore, accurate and appropriate microstructural analysis is crucial to understanding the effects of changes in sputtering parameters. In this work we introduce a cumulative percentage frequency plot that is superior in representing and comparing grain size distributions. The advantages of the cumulative method are demonstrated by discussing the outcome of applying a CoCr interlayer between the magnetic layer and the underlayer. Cumulative percentage frequency plots show that a log-normal distribution fits the grain size data best. In addition, applying an interlayer was found to result in improved magnetic properties.

Demonstration and characterization of greater than 60 Gb/in/sup 2/ recording systems

We have successfully demonstrated longitudinal recording at areal densities greater than 60 Gb/in/sup 2/ at data rates as high as 160 Mbps (20 MB/s) and at a Bit-Aspect-Ratio (BAR) of 5.7, using merged inductive-write/spin-valve-read heads with microactuators on low noise thin film disks. The heads were fabricated with standard photolithography and wafer pole trimming used in currently available commercial products. At track densities of 60 KTPI and higher, traditional servoing mechanisms are not adequate. With the use of a microactuator, we can further improve the track density by 15%, the linear density by 10% and the areal density by more than 20%. Thus, using a microactuator with the 50 Gb/in/sup 2/ head/media combination, we have increased our areal density achievement up to 63.2 Gb/in/sup 2/.

Demonstration and characterization of 36 Gb/in/sup 2/ recording systems

We have successfully demonstrated recording at areal densities as high as 36 Gb/in/sup 2/ at data rates as high as 173 Mbits/s (21.6 MB/s) and at a Bit-Aspect-Ratio (BAR) of 7.3, using merged inductive-write/spin-valve-read heads on low noise thin film disks. Recording at a data rate of 590 Mbits/s (73.8 MB/s) has also been achieved at the corresponding linear density of 231 KBPI. Comparisons with previous areal density demonstrations have also been summarized.

Magnetic and recording properties of CoCrPtTa thin film media with CrW underlayer

CoCrPtTa thin film media using Cr as an underlayer has been developed as a candidate for future high density longitudinal recording. In an effort to reduce the lattice mismatch between the Cr underlayer and the magnetic layer, the Cr underlayer has been doped with various elements. In this work the effect of adding Wx (x=10 and 15 at. %) to the Cr underlayer on the magnetic, crystallographic, and recording properties are reported. CrW10(Cr90W10) underlayer produced about 400 Oe higher coercivity and higher S* at Mrt≈0.60 memu/cm2 compared to the Cr underlayer. Also at 240 kfci recording density for CoCrPtTa/CrW10 media the normalized media noise was similar and signal-to-noise ratio was about 2 dB higher compared to the CoCrPtTa/Cr media. For the CrW15(Cr85W15) underlayer at Mrt≈0.60 memu/cm2 the coercivity was about 300 Oe higher with S*=0.88, but the normalized media noise was also higher than the CoCrPtTa/Cr media. The x-ray diffraction data suggest better lattice match between the CoCrPtTa/CrW10 media...

Effect Of Track Edge Erasure And On-track Percolation On Media Noise At High Recording Density In Longitudinal Thin Film Media

In this work the experimental evidence of the effect of track edge erasure and on-track percolation on media noise is investigated using Magnetic Force Microscopy (MFM) for CoCrTaPt/Cr thin films deposited at different substrate temperatures (T/sub s/). As the recording density increases from 60 to 146 kfci, the track edges begin to erase and the effective track width reduces, causing a subsequent drop in the read back signal and increase in media noise. Also with the increase in recording density the bit length reduces and the transition boundaries get closer to each other. As a result, the transition boundaries are no longer sharp and show onset of percolation. The onset of on-track percolation for films deposited at 160/spl deg/C with higher exchange interaction occurs at lower recording density compared to the film deposited at 235/spl deg/C. The track edge percolation occurs at lower recording density than the on-track percolation for both samples.

Effect of very thin Cr-underlayer on the magnetic and recording properties of CoCrTa thin-film media

A process has been developed which uses very thin Cr-underlayer for CoCrTa-media for high-density recording. The media sputtered using this technique revealed that by decreasing Cr-underlayer thickness from 2000 /spl Aring/ to 200 /spl Aring/, orientation-ratio increased from 1.27 to 1.6, squareness-ratio increased from 0.81 to 0.86, and Mrt increased from 3.25 to 3.97 memu/cm/sup 2/. The Mr value is increased because of the higher squareness. The higher Mr gives a higher Mrt product which produced higher signal output by about 10%. Also, the noise performance was comparable for the media with thin and thick Cr-underlayers. X-ray diffraction patterns showed strong in-plane preferred orientations, Cr(200) and Co(112~0) textures as a function of Cr-underlayer thickness. >

26.5 Gb/in/sup 2/ areal-density longitudinal thin film media

A 26.5 Gb/in/sup 2/ areal-density demonstration was made using low-noise, thermally stable media and advanced dual-spin-valve heads. The demonstration was achieved at a linear density of 504 kbpi, a track density of 52.6 ktpi, and a data transfer rate of 230 Mb/s. The media had M/sub r/t of 0.40 memu/cm/sup 2/ and coercivity of 2500 Oe, and were composed of a dual-magnetic-layer structure with a five-element magnetic alloy. It was observed that smaller, uniform and isolated magnetic grains are critical to reducing the media noise and for designing ultra-high areal-density recording media that are thermally stable.

Coercivity-gradient bi-layered thin-film media for longitudinal recording

A new coercivity-structure was proposed, and a new process technique was developed for controlling the Hc of second and subsequent magnetic-layers in multi-layer media. A narrow slit cathode was used to sputter Cr-interlayer. Conventional and new Hc-gradient CoCrTa-bi-layer media were sputtered by varying Cr-interlayer thickness 0-25 /spl Aring/ with fixed Cr-underlayer and magnetic layers. In one case, to achieve higher Hc for the top-magnetic layer, Hc gradient bilayer media of Mrt:3.6 memu/cm/sup 2/ were sputtered by using 250 V DC-bias during second magnetic-layer deposition which produced about 300 Oe higher Hc for the top-layer. The bi-layer media reduced media-noise about 30% and increased SNR about 5 dB in comparison to mono-layer media at 66.3 KFCI recording-density. However, conventional bi-layer media produced about 6-7 dB lower overwrite (OW) in comparison to mono-layer media, whereas the new Hc-gradient bi-layer media with higher Hc showed about 5 dB higher OW and 5-12% higher HF-amplitude in comparison to conventional bi-layer media. >