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Exchange-modulated patterned/self-assembled magnetic recording media

IP.com Disclosure Number: IPCOM000016666D
Publication Date: 2003-Jul-08
Document File: 6 page(s) / 226K

Publishing Venue

The IP.com Prior Art Database

Abstract

A perpendicular magnetic recording medium has a patterned or self-assembled magnetic layer and a continuous magnetic layer.

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Exchange-modulated patterned/self-assembled magnetic recording media

      In longitudinal magnetic disk recording, scaling to higher areal densities has historically relied on a continuous reduction of the magnetic grain size and the width of the grain size distribution in recording media in order to keep medium noise within acceptable limits. In contrast, the number of magnetic grains per bit cell has been reduced only slowly. The reduction of the average grain size has in turn led to a reduction of the stability factor for thermal magnetization reversal, which is expressed as the ratio of the stored magnetic energy, KUV (KU: magnetocrystalline anisotropy, V: magnetic switching volume), to the thermal energy, kBT. A minimum stability factor of about 65 is needed to avoid thermally driven demagnetization of bit transitions and therefore loss of data within the desired storage period of about 10 years. Accordingly, grain size reductions can be compensated by increases in KU and therefore the coercivity, HC, of the recording medium. However, while potential medium materials with sufficiently high KU are known, this approach is limited to values of HC lower than about half the maximum head write field in order for the head to be able to write the medium. For the best write pole materials known today, e. g. CoNiFe alloys with a saturation field of about 2.4 T, this results in a write field of about 1.2 T for longitudinal recording, allowing a maximum HC of about 6000 Oe. Perpendicular magnetic recording using a single pole head and magnetic media with a soft magnetic underlayer is being investigated as a means to increase the effective head field by about a factor of 2. Beyond this, a number of alternative solutions to extend magnetic recording towards areal densities in the range of 1 Tbit/in2 have been proposed. Among these are ideas that could be realized using current medium materials, but with a significantly reduced number of grains per bit. The extreme case would involve only one "grain" per bit, an approach known as patterned medium. The bit can be defined via either lithography [1, 2] or self-assembly [3]. However, further reduction of the magnetic grain size of patterned media or self-assembled media will ultimately be limited by thermal decay. Furthermore, in order to realize the benefit of patterned/self assembled media, very narrow distributions of grain size and magnetic properties for each grain will be necessary, which in turn will require extremely tight control of the fabrication processes.

    In granular perpendicular recording media it has been shown that optimizing the exchange coupling between grains is an effective method for improving SNR and thermal stability of the written bits [4].

    The invention presented in the following describes a method to achieve improved thermal stability and SNR in patterned/self-assembled media by effectively controlling the exchange coupling between the individual grains/bits.

Description o...