Ultrasmall grain size control in longitudinal recording media for ultrahigh areal densities

Abstract

In this study, we propose a new “atomic wall” approach to underlayer design. In this design, a CrX underlayer is used where X and Cr are not miscible in the bulk phase, resulting in a reduced grain size. We have studied the addition of Zr to Cr layers and found that CrZr gives magnetic properties comparable to those of CrMo underlayers. In addition, a CrZr underlayer gives rise to a smaller grain size of 5.5 nm, in comparison to a grain size of 6.2 nm in the case of CrMo underlayers. To our knowledge, this is the smallest grain size reported for Co-alloy recording media. The recording measurements also show a higher signal to noise ratio for CrZr underlayers than for CrMo underlayers, suggesting that CrZr underlayers have potential for use in ultrahigh areal densities.

Grain Size Reduction by Doping Cr Underlayer with Ru for Longitudinal Magnetic Recording Media

“…2(b). The coercivity increases from 5-30 nm because the Co(11.0) orientation is improved [1]- [4]. When the thickness of the underlayer exceeds 30 nm, the doping of the Cr underlayer with Ru increases the coercivity, by improving the preferential alignment of -axis in the plane [3].…”

“…However, adding these elements does not significantly reduce the grain size. The Cr underlayer was doped with Zr [1], [2], [4], Nb [2] and B atoms [9] to reduce the magnetic grain size, because these elements are insoluble in Cr lattices, and thus segregate in the grain boundaries, preventing further grain growth. Although doping with these elements reduces the magnetic grain size, the Co(11.0) orientation was poor and the coercivity was low [1].…”

Recording media research for future hard disk drives

“…In this case, the small grain size achieved in RuAl underlayers helps to obtain small grain size in the RLs. Therefore, reducing the grain size of the FePt media by controlling the underlayer grains is one possible approach, which is not very different from what has been used in longitudinal and perpendicular recording media of the past [4,40,41]. In addition, attempts have also been made to dope FePt with additives such as C, Ag, Cu, to reduce the grain size and intergranular segregation.…”

“…Because of such randomness in the nature of the grains used for storing the information, a group of grains are used. As the signal-to-noise ratio (SNR) from such a medium depends on the number of grains in a bit, reduction in grain size and grain size distribution are achieved by the use of seedlayers or underlayers with small grain sizes or from the magnetic layer itself [3][4][5][6]. In order to minimize the noise from the randomness, underlayers such as Cr and the concepts such as orientation ratio (OR) were used.…”

High-energy product exchange-spring FePt/Fe cluster nanocomposite permanent magnets

“…Cluster-assembled magnetic materials have received significant attention because of the many potential applications [1,2]. Particularly, cluster assembly offers the opportunity to produce tailored nanostructures with excellent control of scale and phase fraction.…”