L10-ordered high coercivity (FePt)Ag–C granular thin films for perpendicular recording

Heat-assisted magnetic recording (HAMR) media status, requirements, and challenges to extend the areal density (AD) of magnetic hard disk drives beyond current records of around 1.4 Tb/in.2 are updated. The structural properties of granular high anisotropy chemically ordered L10 FePtX-Y HAMR media by now are similar to perpendicular CoCrPt-based magnetic recording media. Reasonable average grain diameter ⟨D⟩ = 8–10 nm and distributions σD/D ∼ 18% are possible despite elevated growth temperatures TG = 650–670 °C. A 2× reduction of ⟨D⟩ down to 4–5 nm and lowering σD/D < 10%–15% are ongoing efforts to increase AD to ∼4 Tb/in.2. X = Cu ∼ 10 at. % reduces the Curie temperature TC by ∼100 K below TC,bulk = 750 K, thereby lowering the write head heat energy requirement. Multiple FePtX-Y granular layers with Y = 30–35 vol. % grain-to-grain segregants like carbides, oxides, and/or nitrides are used to fully exchange decouple the grains and achieve cylindrical shape. FePt is typically grown on fcc MgO (100) seedlayers to form well oriented FePt (002). A FePt lattice parameter ratio c/a ∼0.96 and high chemical order S > 0.90 result in magnetic anisotropy KU ∼ 4.5 × 107 erg/cm3, and only 25% below the FePt single crystal value KU = 6.6 × 107 erg/cm3 has been achieved in 7–8 nm diameter grains. Switching field distributions depend on anisotropy field (HK) distributions, which are currently of the order of ΔHK/HK ∼ 10% (ΔHK ∼ 10–12 kOe, HK ∼ 10–11 T) at room temperature. High thermal conductivity heat sink layers, including Ag, Au, Cu, and Cr, are used to optimize the cooling rate and maximize the down- and cross-track thermal gradient, which determines the achievable track density.

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“…%) film produces spherical magnetic grains and a bimodal distribution of magnetic grain sizes. 24 Zhang et al 77 and Varaprasad et al…”

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confidence: 99%

Review Article: FePt heat assisted magnetic recording media

Weller¹,

Parker²,

Mosendz³

et al. 2016

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

159

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“…The typical size of grains is around 5 nm wide and 7 nm thick 16 , where grains are separated by a 1 nm thick C matrix 17 . This matrix ensures thermal isolation, as well as magnetic exchange isolation.…”

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confidence: 99%

Model for multishot all-thermal all-optical switching in ferromagnets

2016

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All optical magnetic switching (AOS) is a recently observed rich and puzzling phenomenon that offers promising technological applications. However, fundamental understanding of the underlying mechanisms remains elusive. Here we present a new model for multi-shot helicity-dependent AOS in ferromagnetic materials based on a purely heat-driven mechanism in the presence of Magnetic Circular Dichroism (MCD). We predict that AOS should be possible with as little as 0.5% of MCD, after a minimum number of laser shots. Finally, we reproduce previous AOS results by simulating the sweeping of a laser beam on an FePtC granular ferromagnetic film.

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“…5 Perumal et al reported that the FePt-C system yields a well-isolated FePt granular microstructure with a small size distribution. 6 Thereafter, Zhang et al optimized both the microstructure and magnetic properties of the (FePt) 0.9 Ag 0.1 -40vol.%C granular films, 7 where Ag enhances the kinetics of L1 0 ordering as it is ejected from the FePt particles during growth. 8 One drawback of the FePt(Ag)-C system is its inability of columnar grain growth; i.e., when the overall thickness of the FePt(Ag)-C layer becomes greater than 6 nm, a second layer appears on the top of the initially grown FePt(Ag)-C granular layer.…”

Section: Introductionmentioning

confidence: 99%

“…1 Hence, for practical use of FePt-C granular films as HAMR media, their microstructure must be further optimized on the basis of the following aspects: columnar growth of FePt grains with an aspect ratio larger than 1.5, excellent c-axis alignment of the grains normal to the film plane, and a grain size of less than 6 nm with a size distribution less than 15%. 1,5 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 L1 0 -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 (Mg 0.2 Ti 0.8 )O, 12 and TiON. 13,14 However, growth of well-isolated FePt columnar grains in thicknesses larger than 6 nm has so far been difficult on these underlayers.…”

Section: Introductionmentioning

confidence: 99%

Influence of MgO underlayers on the structure and magnetic properties of FePt-C nanogranular films for heat-assisted magnetic recording media

et al. 2016

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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.

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L10-ordered high coercivity (FePt)Ag–C granular thin films for perpendicular recording

Cited by 179 publications

References 34 publications

Review Article: FePt heat assisted magnetic recording media

Review Article: FePt heat assisted magnetic recording media

Model for multishot all-thermal all-optical switching in ferromagnets

Influence of MgO underlayers on the structure and magnetic properties of FePt-C nanogranular films for heat-assisted magnetic recording media

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