Time Dependence in Perpendicular Media With a Soft Underlayer

Abstract

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract-In this paper we describe measurements of magnetic viscosity or time dependence in magnetic thin films suitable for use as perpendicular recording media. Generally, such effects cannot be measured using conventional magnetometry techniques due to the presence of a thin (0.1 m) soft underlayer (SUL) in the media necessary to focus the head field. To achieve our results we have developed an ultrastable MOKE magnetometer, the construction of which is described. This has enabled us to measure nominally identical films with and without the presence of the SUL. We find that the presence of the SUL narrows the energy barrier distribution in the perpendicular film increasing the nucleation field ( ),reducing the coercivity ( ) and results in an increase in the squareness of the loop. This in turn results in an increase in the magnitude of the viscosity in the region of the but that the range of fields over which the viscosity occurs is reduced.

Anisotropy dispersion in (CoCrPt)1−x(SiO2)x perpendicular recording media

“…In this case the 20 nm SUL of high-magnetisation material generates a magnetic moment, which swamps that from the recording layer. The solution to these difficulties is the application of polar MOKE magnetrometry, but unfortunately rotational experiments are not possible [2]. This means that measurements of the anisotropy axis dispersion in the medium cannot be made using standard techniques such as the variation of remanence with angle [3].…”

Magnetisation reversal in media with perpendicular anisotropy

“…In previous work, we have described our MOKE system that has been specifically designed to enable these measurements to be made at room temperature [8]. A schematic of the MOKE system is shown in Fig.…”

“…Importantly, the apparatus described in Ref. [8] is sufficiently stable to measure time-dependence measurements over a minimum period of 5 min to enable the use of the waiting-time method on samples with an SUL. Hence, it is now possible to characterize magnetisation reversal over the full switching field distribution without the need to correct for the demagnetizing field even when an SUL is present.…”

Activation volumes in CoPtCr-SiO/sub 2/ perpendicular recording media

“…In this paper, was measured by two methods for CoPtCr-SiO media with varying levels of SiO . The first method is based on the sweep-rate dependence of the remanent coercivity using Sharrock's equation [1], [2], and the second is from the measurement of the fluctuation field [3] determined from time-dependence data measured using a highly stable magneto-optic Kerr effect (MOKE) magnetometer [4]. A comparison is made of the values of obtained from the two techniques.…”

“…Volume Fig. 6 shows the time dependence of magnetization in different applied fields for the 8.4 at% SiO sample measured by the highly stable MOKE magnetometer [4]. The fluctuation field can be calculated from these results using the waiting time method [3] and (1) (1) where is the difference in the applied field between two time-dependence measurements, and and are the times at which the data reaches a constant value of magnetization .To reduce experimental error, a number of points are measured in preference to the two points described by (1).…”