Storage Density Beyond 10Tb/in² Possible for HAMR

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Heat-assisted magnetic recording of bit-patterned media beyond 10Tb/in²
Christoph Vogler, Claas Abert, Florian Bruckner, Dieter Suess2 and Dirk Praetorius

Abstract
The limits of areal storage density that is achievable with heat-assisted magnetic recording are unknown. We addressed this central question and investigated the areal density of bit-patterned media. We analyzed the detailed switching behavior of a recording bit under various external conditions, allowing us to compute the bit error rate of a write process (shingled and conventional) for various grain spacings, write head positions, and write temperatures. Hence, we were able to optimize the areal density yielding values beyond 10Tb/in². Our model is based on the Landau-Lifshitz-Bloch equation and uses hard magnetic recording grains with a 5-nm diameter and 10-nm height. It assumes a realistic distribution of the Curie temperature of the underlying material, grain size, as well as grain and head position.
 
Although the basic concept of heat-assisted magnetic recording (HAMR) dates back nearly 60 years, only very recently was the first fully functional drive with more than 1000 write power on hours and a 1.4Tb/in² device demonstrated. To keep up with the continuous increase in areal storage density (AD), one must provide (i) small magnetic grains and (ii) a recording scheme with a high effective write field and temperature gradient in order to allow for small bit transitions. To realize small magnetic grains, high magnetic anisotropy must be used to ensure that the stored binary information is thermally stable. The limited maximum magnetic field of write heads results in the so-called magnetic recording trilemma.

HAMR can help overcome this trilemma. One uses a laser spot to locally heat the selected recording bit near or above the Curie temperature (TC). Hence, even the magnetization of very hard magnetic (HM) materials can be reversed with the available write fields. Nevertheless, thermally written-in errors are a serious problem of HAMR.

In this paper, we demonstrate under which circumstances a bit-patterned recording medium, consisting of hard magnetic single-phase grains with a realistic distribution of the Curie temperature, can have an areal storage density of 10Tb/in², despite thermal fluctuations at high temperatures during writing, which deteriorates the bit transition.