Multilayer Perpendicular Magnetic Recording Media Research Articles

Cross-Sectional Control of Boron Contents and the Microstructures of Co/Pd Multilayer Perpendicular Magnetic Recording Media

The effects of cross-sectional modulated boron segregation on Co/PdB multilayer perpendicular magnetic recording media have been studied. Gradually reduced boron contents from thin PdB seed layer (33 at.%) to the top of the Co(0.2 nm)/PdB (0.8-nm) multilayer (12.5 at.% at the center of the multilayer) were successively achieved and confirmed by the depth-profile of X-ray photoelectron spectroscopy (XPS). Observed magnetic properties and magnetic force microscopy images suggested that this gradient diffusion supports reduction of intergrain exchange coupling and improvement of the magnetic properties. The signal-to-noise ratio over 22 dB was obtained at 450 kFCI in playback tests, in combination with amorphous cobalt boron soft-magnetic underlayer (SUL). It is suggested that these properties are brought by a combination of the dispersed nucleation sites with rich boron content in the initial layer and decreasing boron content during the growth of the multilayer. In addition, this simple medium, which consists of only three elements, Co, Pd, B, for the SUL, the seed layer, and the magnetic layer, has a very unique feature of the dull interfaces, observed by a transmission electron microscope.

Introduction of NiAl as seed layer and domain wall pinning layer for Co-Pd multilayer perpendicular magnetic recording media

The grain size of the Co-Pd multilayer perpendicular magnetic recording media was reduced significantly with the introduction of a NiAl seed layer. The angular dependence of the coercivity data indicated a domain wall pinning effect of the introduced NiAl layer. Improvements were observed in read/write tests on a Co-Pd multilayer medium with a NiAl pinning layer.

Development of CoX/Pd multilayer perpendicular magnetic recording media with granular seed layers

CoCrRu-based granular seed layers are studied to control the hysteresis properties of CoX/Pd multilayer based perpendicular magnetic recording media. Proper choice of the CoCrRu growth conditions is found to reduce the hysteresis slope parameter α and to improve the switching field distribution, suggesting that this granular seed layer is effective in producing exchange decoupled columnar structures. The results are confirmed by magnetic force microscopy studies of recorded patterns as well as by DC/AC-erase noise measurements, remanent coercivity studies and microstructural observations by transmission electron microscopy.

Effect of underlayers on magnetic properties of Co/Pd multilayer perpendicular magnetic recording media

Amorphous C and Si films were sputter-deposited as underlayers of Co/Pd multilayer perpendicular magnetic recording media. The magnetic properties of the media were significantly affected by the underlayer thickness; namely, the values of coercivity H c and nucleation field − H n increased and the value of α decreased with merely increasing the thickness of C or Si underlayer, where α is the derivative of M– H loop at the value of coercivity. The coercivity was not always affected by magnetic anisotropy constant K u for the Co/Pd media. In read–write experiments, the higher S/N ratio was obtained for the media with the thicker C or Si underlayer, which exhibited low α and high H c. In the time decay experiments of magnetization, the Co/Pd multilayer media with C or Si underlayer possessed good thermal stability. This study demonstrated that the introduction of C or Si underlayer greatly improves magnetic properties, read–write characteristics, and thermal stability of Co/Pd multilayer perpendicular magnetic recording media.

Improvement of signal to noise ratio for Co/Pd multilayer perpendicular magnetic recording media by the addition of an underlayer

Signal and noise characteristics of Co/Pd multilayer perpendicular magnetic recording media are discussed based upon MFM analysis. The noise of the Co/Pd multilayer media is originated mainly from irregularities in the magnetic transition regions, and can be drastically suppressed by increasing the thickness of the carbon underlayer although a large number of reversed magnetic domains between the magnetic transitions still exist. The fine magnetic clusters formed in the medium with a thick carbon underlayer result in clear magnetic transition boundaries of recorded bits in the high recording density region. By examining the profile of the M– H loops, the decrement in the α value, which is defined as the slope of M– H loop at the value of coercivity, improves the signal to noise ( S/ N) ratio for the Co/Pd multilayer media.

Magnetic properties and noise characteristics of Co/Pd multilayer perpendicular magnetic recording media

In Co/Pd multilayer perpendicular magnetic recording media, a granular seed layer and the addition of boron and oxygen are effective for reducing medium noise. In a recording system using a conventional ring-shaped head and a perpendicular medium without a soft magnetic underlayer, precise control of the write-current waveform is important to minimize medium noise. Low noise, low non-linear transition and no signal decay are observed for the Co–B–O/Pd–B–O multilayer with an Au–SiO 2 seedlayer.

Analysis of microstructures for Co/Pd multilayer perpendicular magnetic recording media with carbon underlayer

The effect of amorphous carbon underlayer thickness on the microstructure of the Co/Pd multilayer perpendicular magnetic recording media was investigated. From the magnetic force microscopy observation in the AC-demagnetized state of the Co/Pd multilayer media, the magnetic cluster size was observed to effectively decrease with an increase in carbon underlayer thickness, where the higher coercivity and the higher S/ N ratio of the Co/Pd multilayer media were obtained with the thicker underlayer. Furthermore, the distribution of [1 1 1] orientation of FCC-Pd became broader, and the grain size decreased with an increase in the carbon underlayer thickness. These effects caused the magnetic exchange decoupling of Co/Pd multilayer media. We suggested that the change of microstructure was directly related to the surface roughness of the amorphous carbon underlayer.

CoCrPtTa and Co/Pd perpendicular magnetic recording media with amorphous underlayers

The effect of amorphous carbon underlayers on magnetic properties and read-write characteristics of Co/sub 73/Cr/sub 18/Pt/sub 6/Ta/sub 3/ single layer and Co/Pd multilayer perpendicular magnetic recording media were investigated. The increase in H/sub c/ and decrease in /spl alpha/, defined as 4/spl pi/(dM/dH)/sub H=Hc/, were observed by increasing the underlayer thickness for both Co/sub 73/Cr/sub 18/Pt/sub 6/Ta/sub 3/ and Co/Pd media. The media with a low /spl alpha/ value, suggesting a decrease in the exchange coupling, exhibited the higher coercivity and the improvement of S/N ratio. In read-write experiments, the improvement of S/N ratio for the Co/Pd media was achieved up to 400 kFRPI or even higher in the recording density by increasing carbon underlayer thickness, while that for the Co/sub 73/Cr/sub 18/Pt/sub 6/Ta/sub 3/ media was obtained up to ca. 250 kFRPI.

Effect of recording layer thickness on read/write performances of Co/Pd multilayer perpendicular magnetic recording media

Effect of recording layer thickness on read/write performances of Co/Pd multilayer perpendicular magnetic recording media

Low noise Co/Pd multilayer media for perpendicular magnetic recording

Read-write tests and magnetic force microscopy (MFM) observations have been performed for Co/Pd multilayer perpendicular magnetic recording media. For a Co/Pd multilayer medium with a nucleation field (H/sub n/) of/spl sim/1.5 kOe and a small slope at coercivity (Hc), no reversed magnetic domains between the transitions were observed and a low medium noise was also obtained. Moreover, a negligible time decay in magnetization was detected at the remanent state as well as in signals at both low and high recording densities.