L1 0 -ordered FePtAg-C granular thin films for theramlly-assisted magnetic recording media

Transcription

1 L1 -ordered FePtAg-C granular thin films for theramlly-assisted magnetic recording media L. Zhang, Y.K. Takahashi, K. Hono Magnetic Materials Center, National Institute for Materials Science (NIMS) Tsukuba 35-47, Japan B.C. Stipe, J.-Y. Juang, and M. Grobis Hitachi Global Storage Technologies, San Jose Research Center San Jose, CA 95135, USA

2 Goal of Project: FePt HAMR media > 4 Tbits/in 2 Requirement: High K u (>1 7 erg/cc) - L1 -ordered FePt thin film D~4nm with uniform size distribution (1) alignment on commercially viable substrates Our previous work : FePtAg- C granular film Gb/in 2! 1nm Degree of L1 Order:.99 Grain size: 6.1±1.8nm Center to center: 9.6nm C spacing: 3.5nm Thickness : 6.4nm Ra:.45 nm, PV: 5.84 nm H k 65 koe H C.perp = 37kOe H C.inp = 5kOe K u = erg/cc M s =74 emu/cc E b = 7.6eV K u V/k B T = 3 H C =43.6kOe ΔH c /H c =.27

3 Optimized FePtAg-C Granular Film (2) (111) MgO() 8 () (1) θ (degree) (1) alignment is excellent S =.9 8 perp inp M (emu/cc) Intensity (a.u.) H (koe) HC = 35kOe, Ku = 4.3x17erg/cc 6.2±1.4nm

4 HREM image (1)FePt (2)MgO MgO GB There is no one to one correspondence between the FePt particles and MgO grains

5 Energy filted TEM images Zero-loss Ag Fe Pt C O

6 Energy filtered TEM images Zero-loss Ag is dissolved in FePt grains. C falls outside FePt grains, as spacer.

7 Temperature dependence of remanence (M r ) Sample degradation (Ms reduction) suspected Low temperature measurement also supported small J value of.5. T c was estimated to be C. H. Nemoto and I. Takekuma, Hitachi

8 TAR static tester results 92 nm track width 81 nm track width 5 nm 5 nm 45 nm 45 nm 4 nm 4 nm 35 nm 35 nm 3 nm 3 nm 25 nm 25 nm 2 nm 2 nm 15 nm 15 nm 81nm track x 15nm bit ~ 53 Gb/ in2.

9 Op:mized FePtAg- C film 53 Gb/in2! 1 (2) (111) MgO() 8 () (1) Intensity (a.u.) θ (degree) 8 perp inp H (koe) 2 4 Hk HC.perp HC.inp Ku Degree of L1 Order:.9 Ms Eb Grain size: 6.2±1.4nm KuV/kBT Center to center: 9.6nm Hc C spacing: 3.5nm Tc Thickness : 6.4nm 65 koe = 35kOe = 7kOe = erg/cc =74 emu/cc = 5.1 ev = = 37.5 koe = 46-48C

10 Future project directions recommended by ASTC 1. Well segregated and uniform single-column grains!!selection of the matrix!! 2. Reduce the process temperature: for NiP/Al substrate!!addition of the forth element!! 3. ECC and HAMR!! 4. Origin of the in-plane hysteresis loop.!! 5. Use single composite target.!

11 FePt-SiO 2 granular films 8 FePt(4,6)-SiO 2 MgO (1) Oxidized Si. Substrate M (emu/cc) T s = 5 o C H (koe) Intensity (a.u.) (1) FePt(6nm)-5% SiO 2 FePt(4nm)-5% SiO 2 early optimized FePtAgC (111) MgO() () (2) θ (degree)

12 Other spacer material: FePt-B FePt(4)-Bx% MgO (1) FePt-B4% (5.6nm) Oxidized Si. Substrate Intensity (a.u.) (1) Optimized Ag1%-C5% FePt-B% FePt-B2% FePt-B4% (111) MgO() (2) () θ (degree)

13 FePtX-C films (x = Ag, Cu) Fe 49 Pt 41 -X 1-5%C Intensity (a.u.) (1) Cu1% Au1% Ag1% early optimized FePtAgC (111) MgO() () (2) FePtX-C5% (6) MgO (1) Oxidized Si. Substrate θ (degree)

14 FePtX-C films (x = Ag, Cu) Fe 49 Pt 41 Ag 55 o C! 8 perp inp Ag! Fe 49 Pt 41 Cu 1 55 o C! 8 perp inp Cu! M (emu/cc) - - M (emu/cc) H (koe) H (koe)

15 Sputtering using an alloy target (Fe 47.5 Pt 47.5 Ag 5 )-5vol%C ICP:(Fe 56.6 Pt 41. Ag 2.5 )-C Cosputtering (FePt).9 Ag.1 -C5% d=6.1±1.8nm d=6.4 nm d=6.1nm

16 Summary FePtAg-C granular film with H c =35 koe and good squarness was obtained.(d 6.2±1.4 nm) Few FePtAg particles grow on one MgO grain. No 1:1 correlation. Ag dissolved in the FePt particle. T c of FePtAg-C is C. TAR static test at HGST demostrated 53 Gbit/in 2 Similar microstructure can be produced by sputtering alloy targets

17 Future Direction More effort in optimizing the nanogranular structure in a laboratory scale D~4 nm, δ<1%, better SFD Better choice for spacer materials for columnar growth Metallic interlayer instead of MgO Effect of thermal conductance of substrate and interlayer on TAR density Effect of exchange coupling on SFD Y. K. Takahashi et al. Appl. Phys. 1, 7435 (6). Y. K. Takahashi et al. Appl. Phys. Lett. 84, 383 (). suggest parameter choice in industrial production of FePt granular media using alloy targets