Transition curvature is a significant factor in limiting the densities that can be achieved using perpendicular recording. In this report, the transition curvature of a written track is extracted solely from measurements on a spin-stand. Both signals waveforms and background media noise waveforms were captured. By numerical post-processing, the transition shape can be determined by referencing it against the media noise.

The role of intergranular exchange coupling was experimentally investigated in a coupled granular/continuous (CGC) perpendicular medium structure. By changing the number of Co/Pt bilayers in the continuous layer, the degree of exchange coupling can be systematically controlled. The switching field distribution (SFD) was roughly estimated from Kerr loops. The SFD became narrower for media with a thicker continuous layer. Using a head with a single-pole writer and an 80 nm gap giant magnetoresistance reader, reverse dc erase noise was measured as a function of the reverse dc erase current. The media showed a clear positive noise peak with an increase in reverse erase current. Narrowing of the SFD was reflected by narrowing of the noise peak width. However, the peak value of the medium’s noise also increased with an increase in the thickness of the continuous layer. Although exchange coupling increases the average magnetic cluster size in the demagnetization condition, CGC media with moderate exchange coupling showed no degradation of the signal to noise ratio compared to the base granular medium.

Summary form only given. We recently proposed a novel perpendicular medium structure that consisted of a continuous layer and a granular layer, referred to as coupled granular continuous (CGC) media, to optimize the medium noise and thermal stability. These media used Co/Pt multilayers as the continuous layer. In this study, a Pt-rich CoPt/sub 22/Cr/sub 22/ alloy film with poor Co-Cr phase segregation is employed as the continuous layer instead of the multilayers, to demonstrate the general concept of the CGC structure. All CGC media had a continuous layer, a Pt buffer layer, and a common 12.5-nm-thick granular layer (CoCr/sub 18/Pt/sub 12/) on a soft magnetic underlayer.

A lithographically patterned magnetic medium is one of the proposed routes to magnetic recording at a density beyond that thought to be possible using conventional recording media due to thermal instability caused by superparamagnetism. Using a focused ion beam to pattern a granular Co/sub 70/Cr/sub 18/Pt/sub 12/ film, we have fabricated sub-80-nm size islands that are single domain and with a narrowed switching field distribution and an enhanced thermal stability. Magnetic isolation of the islands is shown to be a result of vanishing of magnetic remanence and coercivity in the irradiated region and not a result of sputtering. Recording measurements using a quasi-static giant magnetoresistive head demonstrate the sensitivity to detect single 80-nm islands. The readback jitter from the patterned region is dramatically reduced compared to that measured for continuous media at the same linear density.

Fabrication, magnetic properties, and read/write characteristics of coupled granular/continuous (CGC) perpendicular media are described. The media consist of continuous Co/Pt multilayers, which have a strong in-plane exchange coupling, and a granular CoCrPt layer on top of a soft magnetic underlayer. These continuous and granular layers are magnetically coupled, thus the switching field distribution becomes effectively narrower. Recording measurements using a single-pole writer and a giant magnetoresistive reader show substantial improvement in the head output and resolution of the CGC medium, compared to the plain granular medium. Transition jitter and medium noise are reduced in the CGC media. As a result, the CGC media have 3–5 dB higher signal-to-noise ratio (SNR) and better thermal stability than the plain granular medium. The concept of CGC perpendicular media is a viable way to achieve both the thermal stability and medium SNR requirements for high-density recording.

We investigated coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer for high thermal stability and a granular host layer to reduce noise. The addition of Co/Pt multilayers increased the nucleation field of the CoCr18Pt 12 medium from 0 to -2000 Oe. Moreover, the moment decay was reduced from 4.8% to 0.1% per decade. Compared to Co/Pd multilayer media, the CGC medium had a 10 dB higher signal-to-noise ratio (SNR). The granular host layer significantly improved the SNR in the high-density region over 10 kfc/mm. Compared to the CoCr20Pt 10 medium, the CGC medium had a 3 dB higher SNR in the low-density region. The medium noise for the CGC medium increased with the recording density, while the noise for the CoCr20Pt10 medium remained constant from 10 to 20 kfc/mm. The approach using CGC medium improves both the SNR and the thermal stability

Perpendicular medium with an average grain size of 8.2nm with 20nm thickness has been produced by using a-CoCrPt/Ti/NiAl tri-layer structure. The signal-to-noise ratio improves with the addition of a NiAl seed layer. From the TEM image analysis, the introduction of the NiAl seed layer may enhance the separation between the CoCrPt grains. The ultra-small grain size will improve the performance of perpendicular media for future high-density recording applications.

We studied coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer structure and a granular layer. The addition of Co/Pt multilayers decreased the nucleation field from 200 to −1800 Oe and increased the squareness from 0.9 to 1.0. The moment decay at room temperature was significantly reduced from −4.8% to −0.05% per decade. At elevated temperatures, strong exchange coupling between a granular layer and a continuous layer is needed for thermal stability. The exchange-coupled continuous layer reduces thermal demagnetization as it effectively increases the grain size, tightens the grain distribution, and prevents the reversal of individual grains. Magnetic Force Microscope image showed a larger magnetic cluster size for the CGC structure. Compared to the CoCr18Pt12 medium, the CGC medium had 2.3 dB higher output. However, the noise for the CGC medium increased with the recording density, while the noise for the CoCr18Pt12 medium remained constant from 4 to 15 kfc/mm. Further optimization and noise reduction are still required for future high density recording.

Perpendicular medium with an average grain size of 8.2 nm have been produced by using a-CoCrPt/Ti/NiAl tri-layer structure. The signal-to-noise ratio for the tri-layer medium is 2-7 dB higher than CoCrPt/Ti bi-layer medium at low deposition temperatures. The medium noise is dominated by dc noise and exhibits little transition noise for densities less than 500 kFCI. The ultra-small grain size will improve the performance of perpendicular media for future high-density recording applications.