Magnetic Properties of Hard/Soft-Stacked Perpendicular Media Having Very Thin Soft Layers with a High Saturation Magnetization

Abstract

The magnetic properties and recording performance of hard/soft-stacked media consisting of a magnetically hard layer (9-10 nm) underneath a very thin soft layer (2 nm) with a large saturation magnetization were investigated. Magnetic energy calculations revealed that reducing the strength of the interfacial exchange coupling between the hard and soft layers reduces the remanence coercivity, Hr. Moreover, an increase in the saturation magnetization of the soft layer <Ms soft > significantly enhances the Hr reduction. It is theoretically predicted that the grain volume of hard (10 nm)/soft (2 nm) stacked media having <Ms soft > of 1000 emu/cm 3 could be reduced to about 1/3 that of conventional media whilst maintaining good recording writability and thermal stability. An experimental study of stacked media revealed that the magnetization reversal mechanism changed systematically as a function of the strength of the interfacial exchange coupling, as predicted theoretically. The Hr reduction on adjusting the interfacial coupling reached 22% of that of media consisting of directly coupled hard/soft grains. It was successfully demonstrated that hard/soft-stacked media having thin soft layers with a large <Ms soft > showed better recording writability without degradation of SNmR, recording resolution, or thermal stability.

Effect of interlayer exchange coupling on magnetization reversal process in ECC media with high coercivity

“…Magnetization of the soft and hard layers is simultaneously reversed due to the strong interlayer exchange coupling between two layers when A interlayer is 10.0×10 7 erg/cm. Such a magnetization reversal process is hereafter denoted as coherent rotation [4]. Magnetization reversal in the soft layer occurs faster compared to the hard layer when A interlayer is 5.0×10 7 erg/cm.…”

“…Berger et al investigated the effect of interlayer exchange coupling on the recording performance in the ECC media by experiments [3]. Moreover, Inaba et al reported that the interlayer exchange coupling is closely related to magnetization reversal process in the ECC media, and that the magnetization reversal process is divided into three modes, which are spinflop, incoherent, coherent rotation modes [4]. However, although the magnetization reversed process in the ECC media is one of important issues in order to achieve further ultrahigh recording density, the timeevolutional magnetization process in the ECC media with high coercivity has not been sufficiently discussed yet.…”

Effect of layer thickness ratio on magnetization reversal process in stacked media with high coercivity

“…It is found that during applying the H a the magnetization of the soft layer is printed first in accordance with the pattern of master, and that magnetization reversal of the hard layer follows slightly behind that of the soft layer. This magnetization reversal process is equivalent to incoherent rotation [3]. of the soft layer is reversed during applying the H a , magnetization in the hard layer hardly changes as shown in Figs.…”

“…Namely the magnetization of each layer is independently reversed. This magnetization reversal process is equivalent to spin-flop rotation [3]. -7 erg/cm.…”

“…It is important to elucidate magnetization change in soft and hard layers of the stacked media at the time of recording, where interlayer exchange coupling between the layers has an essential role for the magnetization change [3] - [6]. The thickness of the soft layer is generally from about 1/5 to 1/3 of the hard layer in stacked media of commercial hard disks.…”