Development of high density magnetic recording media for hard disk drives: materials science issues and challenges

Abstract

The tremendous increase in areal density of hard disk drives is mainly ascribed to harmonic development between magnetic recording media and heads in their scaling, especially allowing a commercial transition from the longitudinal to perpendicular recording system. This paper reviews the main features, recent breakthroughs and future potentials of both the longitudinal and the perpendicular media from a viewpoint of materials science. Special attention is firstly paid to the 'trilemma' problem for the media, i.e. the compromise among writability, thermal stability and signal to noise ratio (SNR). The evolution of media materials these years are then addressed with emphasis on the thermodynamic origin of magnetically induced phase separation of Co-Cr based alloys, which governs media noise and coercivity, and its applications to the current longitudinal media. The materials challenges for media to achieve 500 Gb in. 22 and above are further predicted from the viewpoints of thermal stability improvement and microstructure control of media materials, and their engineering issues have been discussed for the current Co-Cr based alloys, potential FePt and CoPt ordered, phase separated Co-W based alloys and magnetic rare earth compounds. Finally, the future media approaching 1 Tb in. 22 and beyond are addressed with respect to the principles, progress, engineering challenges and future directions.

Sputtered amorphous Co–Pt–P thin films for soft underlayer of perpendicular magnetic recording

“…The presence of SUL supplies a return flux path from the main pole of the head to the return pole and enables to obtain higher writing fields [4][5][6][7]. If higher writing fields are achieved, materials with higher magnetocrystalline anisotropy energy can be used as recording media, and smaller sized grains can be obtained against superparamagnetic limit and thus higher SNR and areal density can be achieved [8]. The SUL acts also as a magnetic mirror for recording layer, which facilitates the recording layer to generate substantially stronger read-back signals and further improves the thermal stability [9,10].…”

Effect of boron addition on the structure and magnetic properties of CoPt nanoparticles

“…Nanoparticles with strong magnetic anisotropy energy, such as CoPt with the fct L1 0 structure, have been continuously studied as potential candidates for replacement of the current recording media materials. [1][2][3] There remain two problems to be resolved before these materials can be used practically.…”

Energy barriers in patterned media

“…The energy barrier in current hard disk technology is chosen to ensure a data stability for at least 10 years (Qin et al, 2009). This means that a hard disk left for a (much) longer time will not be readable anymore, even if the data format in which the information is stored is still supported.…”

“…This means that the energy barrier needs to be sufficiently high to store information on a hard disk and keep the information for at least 10 years, which is the acceptable storage time for hard disks (Qin et al, 2009). This energy barrier is directly related to the storage density as the height of the energy barrier is the product of the magnetic anisotropy and the magnetic volume.…”

“…Since the write field of magnetic recording heads is limited, at one point the medium becomes unwritable. These problems (stability, SNR and writability) form a trilemma and solutions which keep a high SNR while ensuring thermal stability and which can be written by a magnetic head, need to be found (Qin et al, 2009). …”