Abstract
In order to optimize the nanogranular structure of FePt-C for heat-assisted magnetic recording media, we investigated the influence of MgO underlayers on the growth of FePt grains in the FePt-C layer. The FePt-C layer was deposited by using the alternating sputtering method, by which FePt and FePt-C layers were alternately deposited. To understand the growth mechanism of the FePt-C layer on the MgO underlayers deposited under various conditions, detailed plan-view and cross sectional transmission electron microscopy observations were made for different film thicknesses. We found that columnar FePt grains grow only when the deposition conditions of the MgO underlayer are optimal. Direct TEM observation of the growth process of the FePt-C layer revealed that the number density of nuclei is sufficient in the initial stage of the film deposition; however, coarsening of the grains after grain impingement causes a substantial decrease in the number density of the FePt grains.
Highlights
IntroductionA lot of effort has been devoted to fabricating L10-ordered FePt-C films on glass substrates through underlayers for c-axis alignment of FePt grains to the normal direction of the films, e.g., by using MgO,[4,10,11] (Mg0.2Ti0.8)O,12 and TiON.[13,14] growth of well-isolated FePt columnar grains in thicknesses larger than 6 nm has so far been difficult on these underlayers.[1,12,13,14] Recently, Hellwig et al reported columnar grain growth by modifying the
L10-FePt films with carbon as a segregant to isolate nano-sized ferromagnetic grains are the most promising material for next-generation heat-assisted magnetic recording (HAMR) media that will have recording densities exceeding 1 Tb/in2.1,2 Since the high magnetocrystalline anisotropy (Ku = 6.6 MJ/m3) of the L10-FePt phase gives sufficient thermal stability to the magnetization even for 4-nm grain sizes,[2,3,4] FePt-based media may have recording densities as high as 4 Tbit/in2.5 Perumal et al reported that the FePt-C system yields a well-isolated FePt granular microstructure with a small size distribution.[6]
In order to understand the difference in the microstructure of the FePt-C (12 nm) layers grown on the MgO underlayer deposited at 0.67 and 5.2 Pa Ar, i.e., formation of the second layer and columnar growth of grains, we studied the relationship between the FePt-C layer and MgO underlayer in more detail
Summary
A lot of effort has been devoted to fabricating L10-ordered FePt-C films on glass substrates through underlayers for c-axis alignment of FePt grains to the normal direction of the films, e.g., by using MgO,[4,10,11] (Mg0.2Ti0.8)O,12 and TiON.[13,14] growth of well-isolated FePt columnar grains in thicknesses larger than 6 nm has so far been difficult on these underlayers.[1,12,13,14] Recently, Hellwig et al reported columnar grain growth by modifying the The grain size of the FePt-C films can be controlled by varying the substrate temperature and the volume fraction of C.7,9 A lot of effort has been devoted to fabricating L10-ordered FePt-C films on glass substrates through underlayers for c-axis alignment of FePt grains to the normal direction of the films, e.g., by using MgO,[4,10,11] (Mg0.2Ti0.8)O,12 and TiON.[13,14] growth of well-isolated FePt columnar grains in thicknesses larger than 6 nm has so far been difficult on these underlayers.[1,12,13,14] Recently, Hellwig et al reported columnar grain growth by modifying the
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