GRADED MEDIA: Towards to more than 1 Tbit/in 2 magnetic recording. Dr. D. Niarchos. Th. Speliotis V. Alexandrakis G. Giannopoulos

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1 IMS, NCSR Demokritos Athens, Greece GRADED MEDIA: Towards to more than 1 Tbit/in 2 magnetic recording Dr. D. Niarchos Th. Speliotis V. Alexandrakis G. Giannopoulos

2 CAN YOU IMAGINE ~7 Billion People on 2.5 Hard DISK!!!!

3 TOWARDS MULTITERABITS Fig. 3. Various array of bit patterned media J.Fidler and W. Lee-TUW

4 Longitudinal vs perpendicular recording Max ~ 200 Gbits/in 2 Max ~ 2-3 Tbits/in 2

5 TOMORROW S SITUATION

7 ISCHULLERFEST-MADRID-OCT-2011

8 ISCHULLERFEST-MADRID-OCT-2011

9 MEDIA DESIGN CONSTRAINT-TRILEMMA SYMPOSIUM

10 OVERCOMING THE SUPERPARAMAGNETIC LIMIT

11 OUR GRAND CHALLENGES Material of Choice: FePt -Time - Temperature ISCHULLERFEST-MADRID-OCT-2011

12 EXCHANGED COUPLED MEDIA (ECM) LOWER THE H sf Single Phase Graded Media ISCHULLERFEST-MADRID-OCT-2011

13 EXCHANGE SPRING MEDIA Graded exchange spring media Bilayer Graded SOFT SOFT K U K U(z) HARD K U HARD

EXCHANGE SPRING MEDIA Graded exchange spring media: Tailoring the K u Graded Methods for anisotropy tailoring SOFT HARD K U(z) -Co-deposition of Hard/Soft phases (FePt/Fe) -Co-Deposition

14 EXCHANGE SPRING MEDIA Graded exchange spring media: Tailoring the K u Graded Methods for anisotropy tailoring SOFT HARD K U(z) -Co-deposition of Hard/Soft phases (FePt/Fe) -Co-Deposition of Hard /non magnetic (dilution) (FePt/Al 2 O 3 ) - Deposition by selecting the same hardphase (FePt) and varying the temperature (OUR METHOD) -Benefits -No interfaces, uniform structure

$diffraction SOFT K U(z) HARD FIG.2. (002) Rocking curves of hard(11.$ 5nm)fept(l10)/graded(30 nm)fept(l10 to A1) Composite (solid squares) and 5 nm

450 0C (open triangles) and (200) rocking curves of 5 nm single layers

15 PART II- a: FePt fct / fcc ESM Experiment-Quality of films raded X-ray diffraction SOFT K U(z) HARD FIG.2. (002) Rocking curves of hard(11.5nm)fept(l10)/graded(30 nm)fept(l10 to A1) Composite (solid squares) and 5 nm single layers deposited at different temperatures C (open squares), C (open triangles) and (200) rocking curves of 5 nm single layers deposited at 300 0C (solid triangles) and RT (solid circles). The scale of intensity axis is logarithmic.

16 FePt fct / fcc Magnetic properties m (memu/cm 2 ) H c (koe) Single Hard 11.5nm Hc ~ 34 koe Hc vs thickness of graded layer H film H_ _film H (koe) Hc C Hc C Hc C Thickness t g (nm) Reduction of Hc Graded Hard 11.5nm / Graded 16 nm Hc ~ 2kOe SOFT HARD Switching mechanism Domain wall motion m (memu/cm 2 ) K U(z) H sw /H sw,0 H film H_ _film z EA θ H (koe) Hc vs theta H Film plane Domain wall theory 1/cosθ θ [deg] Hard 11.5nm / graded 12.5nm Hard 11.5nm / graded 9nm

17 MODEL of L1 0 /A1 FePt/FePt GRADED MEDIA Selective samples

18 MODEL of L1 0 /A1 FePt/FePt GRADED MEDIA TEM STUDIES

19 MODEL of L1 0 /A1 FePt/FePt GRADED MEDIA FIG. 1. (Color online) (a) The phase graded media model for the case of the linear phase transformations with 15 nm thick graded layer. (b) Phase profile comparison between the linearly, logistically graded media and bilayer. The bilayer consists of only hard and soft layers.

MODEL of L1 0 /A1 FePt/FePt GRADED MEDIA Switching fields and Energy Barrier FIG. 2. (Color online) (a) Schematic structure of the phase graded media and averaged stacked graded media.

20 MODEL of L1 0 /A1 FePt/FePt GRADED MEDIA Switching fields and Energy Barrier FIG. 2. (Color online) (a) Schematic structure of the phase graded media and averaged stacked graded media. (b)comparison of the switching field between the graded media and the bilayer. (c) Minimum Comparison of the energy barrier as a function of the graded layer thickness. For the bilayer, the x axis in (b) and (c) describes the thickness of the soft layer.

21 MEDIA DESIGN CONSTRAINT-TRILEMMA

22 FePt-C Deposition 1. Why FePt-C? --- Another way to tune the anisotropy --- Reduce size of grains --- Media with lower noise SNR~ SQRT(N)!

23 FePt & C Co-Sputtering Exchange coupling reduction and Hc increment Drastic changes in microstructure isolated grains formation Not affect significantly L10 formation Grain size reduction ( FePt grains <10nm )

C percentage in FePt-C films <30% Hc reduction due interconnected particles Max Hc @30 % vol C isolated grains formation >30% Hc reduction due to FePt grain size reduction &L10 poor transformation

24 C percentage in FePt-C films <30% Hc reduction due interconnected particles Max % vol C isolated grains formation >30% Hc reduction due to FePt grain size reduction &L10 poor transformation SiO 2 /Mgo(10nm)/FePt-C x vol o C[Co- Sputtering ] Perumal et al, J. Appl Phys. 105, 07B732 (2009) Uniformly isolated grains ~10 nm &1 nm grain boundary of C~30 vol. %. Huang et al, J. Appl Phys. 109, (2011)

Maximum Hc (19kOe) @ 15% vol C Similar results 2 layers

25 C percentage in FePt-C films Glass/CrRu(25nm)/Mgo(2nm)/FePt-C(12nm) [ Co- Sputtering ] Maximum Hc 15% vol C Similar results 2 layers structure formation Chen et al, J. Appl Phys.103, 07F517 (2008) Chen et al, Appl Phys Lett. 91, (2007)

26 PAR III: FePt on glass Substrate MgO substrates will never make the future HDs FePt Intermediate layer CrRu Glass Substrate FePt on glass structure - Optimization of : CrRu texture - Growth of the MgO on CrRu - Growth of Single FePt on top Intermediate layer thickness (MgO,Pt) FePt layer temperature and magnetic properties

27 PAR III:CrRu on glass Substrate Optimization of Deposition Temperature for CrRu on Hoya Glass Rocking Curves vs Temperature for CrRu on Hoya Glass

28 PAR III: Intermediate layers X-ray reflectivity CR58: HOYA GLASS/CrRu/MgO(1 nm)/fept FePt Reflectivity Intermediate layer CrRu Glass Substrate Layer Thickness (nm) 2Θ Roughness (nm) Density (g/cm 3 ) FePt MgO CrRu The enhanced density of MgO (4.28 g/cm 3 vs 3.58 g/cm 3 nominal) indicates a degree of mixing either with FePt or with CrRu. This has to be further investigated.

29 PART III-b: Intermediate layers X-ray reflectivity Mass density profile CR58: HOYA GLASS/CrRu/MgO/FePt Blue line: density profile CrRu FePt Depth (nm) MgO

30 PART III-b: Intermediate layers X-ray reflectivity Mass density profile CR57: Si/SiO 2 /CrRu(2 nm)/mgo/fept Blue line: density profile CrRu MgO FePt Depth (nm)

31 Low temperature growth of FePt films On Glass substrates Intensity (arb unit) (001) (111) (002) CrRu(200) CR55HOYA CrRu o C MgO 6nm@33 o C FePt 10nm@350 o C 1,0 CR55HOYA CrRu o C (30nm) MgO o C (6nm) 500 Intensity (arb unit) θ (degree) θ (degree) Magnetization normalized (M/M max ) CR55HOYA CrRu 30nm@150 o C MgO 6nm@32 o C -1,0 Fept 10nm@350 o C ,5 0,0-0,5 FePt o C (10nm) Coercive Field 0.92T Magnetic Field(Oe)

32 Low temperature growth of FePt films On Glass substrates- REPLACE MgO with TiN! MgO Finally we succeeded to deposit FePt(001) on glass With DSI- Singapore DSI-2011

33 MEDIA DESIGN CONSTRAINT-TRILEMMA SYMPOSIUM IC4N-KRITI

34 SYMPOSIUM

Figure 2 SEM images of (a) 15 nm dots of HSQ with a

Figure 5 SEM image of HSQ dots with 30 nm pitch (830

35 Figure 2 SEM images of (a) 15 nm dots of HSQ with a pitch of 38 nm in closed-packed configuration (520 Gbit/in 2 ) with perfect displacement of the dots obtained by multiexposure strategy. Figure 5 SEM image of HSQ dots with 30 nm pitch (830 Gbit/in 2 ). Figure 6 SEM image of HSQ dots with 28 nm pitch (950 Gbit/in 2 ).

36 Unpublished Data-TERAMAGSTOR

37 So, is there life after 10 (or 20,30 ) Tb/in 2? There are clearly limits to conventional HDD technology somewhere in the 1-5 Tbit/in 2 regime, but there are multiple paths forward to around 10 Tbit/in 2 Can we imagine making 4 nm period bits to achieve 40 Tbits/in 2? Density of 2-dimensional storage of all forms (magnetic and semiconductors is approaching limits A 3-D technology breakthrough would seem to be required thereafter, but there is nothing in the horizon(?) DNA-recording would be the ultimate limit of Multi-Multi-TB/in 2

High Anisotropy L1 0 FePt Media for Perpendicular Magnetic Recording Applications

DISKCON 2008 High Anisotropy L1 0 FePt Media for Perpendicular Magnetic Recording Applications Boon Chow LIM Agency for Science Technology & Research (A*STAR) DATA STORAGE INSTITUTE 5 Engineering Drive