Physik: Magnetische Funktionsmaterialien
HAMR

Heat Assisted Magnetic Recording (HAMR)

Heat Assisted Magnetic Recording (HAMR) is expected to be the next technology for increasing the areal density in Hard Disk Drive (HDD) systems [1-2]. In order to shrink bits and magnetic media grains further, currently used CoCrPt media layers in Perpendicular Magnetic Recording (PMR) will be replaced by very high anisotropy FePt L10 granular layers. In order to write such high anisotropy media an additional laser with plasmonic Near Field Transducer (NFT) is used to heat the media locally close to or above its Curie temperature TC during the nanosecond time scale write process, while long term media storage as well as read back occurs at room temperature.

 
Figure 1: Left side: HAMR writing scheme with laser integrated into the write pole. Right side: Close up schematics of the NFT coupling to the granular media layer. The plasmonic energy from the NFT is absorbed in the media grains to heat them up to TC. The thermal energy has to be transported quickly (on the nanosecond time scale) into the heat sink layer below the media in order to achieve narrow bit transitions that support the target densities of 1.5 Tbit/in2 and beyond.
Besides the NFT design with sharp thermal gradients and long life time the small grain FePt L10 media layer structure with columnar grain growth and a grain size below 7 nm is most critical. Obtaining overall thermally and magnetically uniform media with tight distributions in grains size, switching field, and Curie temperature distributions remains very challenging [2-4]. Especially non or only partially ordered as well as mis-oriented grains at a percentage above 5% are not tolerable. In this context a better basic understanding of small grain FePt L10 media growth and viable media optimization procedures is still needed [5-6].

References:

[1] B. C. Stipe, et al., Nature Photonics 4, (2010) 484 – 488.

[2] D. Weller, O. Mosendz, G. Parker, S. Pisana, and T. S. Santos, Phys. Status Solidi A 210, 1245 (2013).

[3] S. Pisana, S. Jain, J. W. Reiner, G. J. Parker, C. C. Poon, O. Hellwig, and B. C. Stipe, Appl. Phys. Lett. 104 (2014) 162407.

[4] S. Pisana, S. Jain, J. W. Reiner, O. Mosendz, G. J. Parker, M. Staffaroni, O. Hellwig, and B. C. Stipe, IEEE Trans. Magn. 51 (2015) 3200205.

[5] S. Wicht, V. Neu, L. Schultz, V. Mehta, S. Jain, J. Reiner, O. Mosendz,  O. Hellwig, D. Weller, and B. Rellinghaus, J. Appl. Phys. 117 (2015) 013907.

[6] S. Wicht, S. H. Wee, O. Hellwig, V. Mehta, S. Jain, D. Weller, and B. Rellinghaus J. Appl. Phys. 119 (2016) 115301.

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