ABSTRACT
Perpendicularmagnetic recording (PMR) in hard disk drives (HDDs)
for computer and consumer electronic applications has been a long-
awaited technology. It was first proposed by S. Iwasaki in 1975
[1] but commercialized in 2005 by Toshiba [2] with 40 GB/1.8-
inch platter (133 Gbits/in2). Implementation of PMR technology has
almost taken three decades due to many challenges and making it
competitive over well-established longitudinal magnetic recording
(LMR) technology. In LMR, a continuous reduction of grain size in
metallic CoCrPt-based alloys is themajor contribution for improving
areal densities. A further increase in the recording density of
≥100 Gbits/in2 needed a grain size smaller than 9 nm and a narrower grain size distribution; this grain size was approaching the
fundamental superparamagnetic limit [3], which leads to thermal
instability in the recording medium. A combination of oriented LMR
media with antiferromagnetically coupled longitudinal magnetic
layers [4] allowed improving thermal stability caused by Mrt (a product of remanent magnetization and thickness) cancellation,
thus partially extending the limit of LMR. A significant increase
of areal density was obtained by introducing PMR technology
with a thicker magnetic recording layer, which provides sufficient
thermal stability and high Mrt as well as high head field strength and gradient. The possibility of PMR to achieve 1 Tbit/in2 was
speculated around 2000 [5, 6]. PMR has made remarkable progress
in the past one decade and the areal density is now approaching
∼920 Gbits/in2. After analyzing different generations of PMR media, significant reduction of magnetic cluster size is highlighted,
while keeping similar structural grain size [7]. Shingled magnetic
recording (SMR) [8] is considered a possible extension of current
PMR technology for areal densities >1 Tbit/in2. SMR media with
track density benefit are developing with similar PMR materials but
advanced head and media design concepts for further improving
areal densities.
