Magnetic Recording. by Gaspare Varvaro. Istituto di Struttura della Materia CNR Nanostructured Magnetic Materials Group

Transcription

1 Magnetic Recording by Gaspare Varvaro Istituto di Struttura della Materia CNR Nanostructured Magnetic Materials Group

2 Outline Brief History of Magnetic Recording Hard Disk Drives General Aspects (Longitudinal Recording) Perpendicular Recording Future Perspectives Final Remarks Slide 2

3 From Telegraphone to Hard Disk Drive 1898 Valdmer Poulsen invented magnetic audio recorder (Telegraphone) ELECTROMAGNET WOUNDED WIRE ANALOG RECORDING WRITING PROCESS M r M r M r3 M r SOUND I(t) H(t) M r (x) M r3 M r2 M r1 H 1 H 2 H 3 H x READING PROCESS M r2 SOUND I(t) B(t) M r (x) I M r1 t Slide 3

4 From Telegraphone to Hard Disk Drive 1898 Valdmer Poulsen invented magnetic audio recorder (Telegraphone) 1930s AEG and BASH developed magnetic audio-tape recorder (Magnetophone) Write/Read Head Ring inductive head Recording Medium Acetate tape coated with a layer of γ-fe 2 O 3 particles Slide 4

5 From Telegraphone to Hard Disk Drive 1898 Valdmer Poulsen invented magnetic audio recorder (Telegraphone) 1930s AEG and BASH developed magnetic audio-tape recorder (Magnetophone) 1956 AMPEX introduced magnetic video recording 1962 Philips invented compact cassette 1976 Panasonic invented VHS system ANALOG RECORDING NO RANDOM ACCESS CAPABILITY Slide 5

6 From Telegraphone to Hard Disk Drive 1898 Valdmer Poulsen invented magnetic audio recorder (Telegraphone) 1930s AEG and BASH developed magnetic audio-tape recorder (Magnetophone) 1956 AMPEX introduced magnetic video recording 1962 Philips invented compact cassette Panasonic invented VHS system IBM invented the first Hard Disk Drive RAMAC Random Access Memory of Accounting and Control Digital recording (0s and 1s) Multiple read/erase cycle Random access capability Capacity = 5 MB 50 Magnetic Disk (diameter = 24 in) Recording density = 2Kb/in 2 Slide 6

7 Areal Density Evolution Longitudinal Recording Perpendicular Recording Future Perspectives Areal Density [Gb/in 2 ] E-3 1E-4 1E-5 1E-6 10 Tb/in2 1 Tb/in Gb/in 2 1 Gb/in AFC Media 1997 GMR Read Head 1990 MR Read Head 1980 Thin Film WR Head 1 Mb/in IBM RAMAC (first HDD, 2 Kb/in 2 ) Longitudinal Recording 2006 Perp. Media TMR Read Head Year 2011 DEMO [Co/Pd] n BPM 1T/in 2 TERAMAGSTOR EU-Project? Perpendicular Recording BPM, High K u Materials, HAMR, ESM, etc. Current HDDs Perpendicular technology Recording Density: 600 Gb/in 2 HDD sold in 2010: 700 million Cost/Gb: 0.02 $ SPINDLE MOTOR VOICE COIL MOTOR DISK RECORDING MEDIUM WRITE/READ HEAD ENCODER & DECODER Slide 7

8 Areal Density Evolution Longitudinal Recording Perpendicular Recording Future Perspectives Areal Density [Gb/in 2 ] E-3 1E-4 1E-5 1E-6 10 Tb/in2 1 Tb/in Gb/in 2 1 Gb/in AFC Media 1997 GMR Read Head 1990 MR Read Head 1980 Thin Film WR Head 1 Mb/in IBM RAMAC (first HDD, 2 Kb/in 2 ) Longitudinal Recording 2006 Perp. Media TMR Read Head Year 2011 DEMO [Co/Pd] n BPM 1T/in 2 TERAMAGSTOR EU-Project? Perpendicular Recording BPM, High K u Materials, HAMR, ESM, etc. Current HDDs Perpendicular technology Recording Density: 600 Gb/in 2 HDD sold in 2010: 700 million Cost/Gb: 0.02 $ SPINDLE MOTOR VOICE COIL MOTOR DISK RECORDING MEDIUM WRITE/READ HEAD ENCODER & DECODER Slide 8

9 Recording Process Longitudinal Recording Perpendicular Recording Future Perspectives Writing current Writing field Magnetic pattern WRITING PROCESS Read head Inductive MR V I Write head Recording Medium Clock window Output voltage from head Data read READING PROCESS Head fringe field Bit Recorded transition Track AREAL DENSITY (Gb/in 2 ) = tpi x bpi tpi = track/in bpi = bit/in Slide 9

10 Write Head I Ring-shaped miniature electromagnet Recording Medium Longitudinal Recording BULK FERRITE INDUCTIVE HEAD Perpendicular Recording Future Perspectives THIN FILM INDUCTIVE HEAD Prepared by photolithographic processes PERPENDICULAR RECORDING Head fringe field Bit Recorded transition Track AREAL DENSITY (Smaller size - Higher working frequency - Higher magnetic density flux) Material µ max (10 3 ) 4πM s (G) H c (Oe) Fe Fe 49 Co 49 V Ni 50 Fe Ni 80 Fe 15 Mo y x d = 20 nm in 2006 High B s High H g < B s High H x > 1.5 H sw (recording medium) High µ High efficiency (low I) Low H c and B r Low Hysteresis Losses Slide 10

11 Read Head BULK FERRITE INDUCTIVE HEADTHIN FILM INDUCTIVE HEAD Longitudinal Recording 1990 ANISOTROPIC MAGNETORESISTIVE HEAD (AMR) Perpendicular Recording Future Perspectives GIANT MAGNETORESISTIVE HEAD (GMR) PERPENDICULAR RECORDING AREAL DENSITY (Smaller size - Higher working frequency Higher sensitivity) V Ring-shaped miniature electromagnet Mechanism Electromagnetic induction Recording Medium Recorded transition Bit Track Slide 11

12 Read Head BULK FERRITE INDUCTIVE HEADTHIN FILM INDUCTIVE HEAD Longitudinal Recording 1990 ANISOTROPIC MAGNETORESISTIVE HEAD (AMR) Perpendicular Recording Future Perspectives GIANT MAGNETORESISTIVE HEAD (GMR) PERPENDICULAR RECORDING AREAL DENSITY (Smaller size - Higher working frequency Higher sensitivity) V Ring-shaped miniature electromagnet Mechanism Electromagnetic induction Recording Medium Recorded transition Bit Track Slide 12

13 Read Head BULK FERRITE INDUCTIVE HEADTHIN FILM INDUCTIVE HEAD Longitudinal Recording 1990 ANISOTROPIC MAGNETORESISTIVE HEAD (AMR) Perpendicular Recording Future Perspectives GIANT MAGNETORESISTIVE HEAD (GMR) PERPENDICULAR RECORDING AREAL DENSITY (Smaller size - Higher working frequency Higher sensitivity) V Mechanism Spin orbit scattering ARM Head ρ max Recording Medium Normalize Resistance ρ min Recorded transition Bit Track Angle between and Slide 13

14 Read Head BULK FERRITE INDUCTIVE HEADTHIN FILM INDUCTIVE HEAD Longitudinal Recording 1990 ANISOTROPIC MAGNETORESISTIVE HEAD (AMR) Perpendicular Recording Future Perspectives GIANT MAGNETORESISTIVE HEAD (GMR) PERPENDICULAR RECORDING AREAL DENSITY (Smaller size - Higher working frequency Higher sensitivity) GMR Effect Discovered in 1988 by Fert and Grünberg (Nobel 2007) FM NM Metal Spacer Mechanism Spin dependent scattering FM Two currents model (Mott s model) There are two conduction channels ( spin-up and spin-down ) that are independent and have different resistances. F. Mott, Proc. R. Soc. Lond Low resistive state High resistive state Slide 14

15 Read Head BULK FERRITE INDUCTIVE HEADTHIN FILM INDUCTIVE HEAD Longitudinal Recording 1990 ANISOTROPIC MAGNETORESISTIVE HEAD (AMR) Perpendicular Recording Future Perspectives GIANT MAGNETORESISTIVE HEAD (GMR) PERPENDICULAR RECORDING AREAL DENSITY (Smaller size - Higher working frequency Higher sensitivity) SPIN VALVE STRUCTURE B.Dieny et al., PRB Free layer Pinned layer FM FM AFM Metal Spacer V Pinned layer Metal Spacer Free layer θ Recording Medium Recorded transition Bit Track Slide 15

16 Read Head 1970 BULK FERRITE INDUCTIVE HEADTHIN FILM INDUCTIVE HEAD Longitudinal Recording Perpendicular Recording Future Perspectives ANISOTROPIC MAGNETORESISTIVE HEAD (AMR) GIANT MAGNETORESISTIVE HEAD (GMR) PERPENDICULAR RECORDING AREAL DENSITY (Smaller size - Higher working frequency Higher sensitivity) SPIN VALVE STRUCTURE B.Dieny et al., PRB Free layer Pinned layer FM FM AFM Metal Spacer V Pinned layer Metal Spacer Free layer Material performance and device fabrication have continuously improved as higher recording densities were achieved. θ Recording Medium Recorded transition Bit Track Slide 16

17 Recording Medium Longitudinal Recording Perpendicular Recording Future Perspectives Magnetic Medium Substrate SEMI-HARD FERROMAGNET It can be permanently magnetized, allowing information to be retained over time. H c M M r M s H Slide 17

18 Recording Medium Longitudinal Recording Perpendicular Recording Future Perspectives Prepared by Dip-coating Prepared by Sputtering Lubricant Overcoat Magnetic Layer Intermediate Layer Underlayer(s) Seed Layer Substrate PFPE (~1 nm) Reduces friction and wear during the head-disk contact Diamond Like Carbon DLC (~1 nm) Provides chemical and mechanical protection CoCr (1-50 nm) Enhances the epitaxy growth of the magnetic layer Cr-based Cr, CrV, CrTi, CrMo ( nm) Controls morphology and texture of the magnetic layer NiAl, CoTi (1-10 nm) Promotes the underlayer texture and morphology Al-Alloy, Glass Performs the role of support (hard, stiff, inert, smooth) MAGNETIC LAYER CoCr(Pt,Ta,B) Alloy (10 nm) Pt Increases K u H sw K u /M s = 4 5 koe Cr Improves grains isolation; Reduces K u Ta,B additives Enhances Cr atoms segregation Granular (<size> = 8 nm) and polycrystalline Co-alloy (HCP) c-axis easy axis 5 nm Core: Co-rich (magnetic) Boundary: Cr-rich (non-magnetic) c-axis Smooth surface (roughness < 5 nm rms) Stoner-Wohlfarth like system Single domain grains Weakly exchange coupled grains Uniaxial in-plane anisotropy K u Slide 18

19 Recording Medium Longitudinal Recording Perpendicular Recording Future Perspectives Prepared by Dip-coating Prepared by Sputtering Lubricant Overcoat Magnetic Layer Intermediate Layer Underlayer(s) Seed Layer Substrate PFPE (~1 nm) Reduces friction and wear during the head-disk contact Diamond Like Carbon DLC (~1 nm) Provides chemical and mechanical protection CoCr (1-50 nm) Enhances the epitaxy growth of the magnetic layer Cr-based Cr, CrV, CrTi, CrMo ( nm) Controls morphology and texture of the magnetic layer NiAl, CoTi (1-10 nm) Promotes the underlayer texture and morphology Al-Alloy, Glass Performs the role of support (hard, stiff, inert, smooth) MAGNETIC LAYER CoCr(Pt,Ta,B) Alloy (10 nm) Pt Increases K u H sw K u /M s = 4 5 koe Cr Improves grains isolation; Reduces K u Ta,B additives Enhances Cr atoms segregation Granular (<size> = 8 nm) and polycrystalline Co-alloy (HCP) c-axis easy axis 5 nm Core: Co-rich (magnetic) Boundary: Cr-rich (non-magnetic) c-axis Smooth surface (roughness < 5 nm rms) Stoner-Wohlfarth like system Single domain grains Weakly exchange coupled grains Uniaxial in-plane anisotropy K u Slide 19

20 Recording Trilemma Longitudinal Recording Perpendicular Recording Future Perspectives Areal Density [Gb/in 2 ] E-3 1E-4 1E-5 1E-6 10 Tb/in2 1 Tb/in Gb/in 2 1 Gb/in AFC Media 1997 GMR Read Head 1990 MR Read Head 1980 Thin Film WR Head 1 Mb/in 2 Longitudinal Recording 1956 IBM RAMAC (first HDD, 2 Kb/in 2 ) 2006 Perp. Media TMR Read Head Year 2011 DEMO [Co/Pd] n BPM 1T/in 2 TERAMAGSTOR EU-Project? BPM, High K u Materials, HAMR, ESM, etc. Perpendicular Recording WRITE-ABILITY SNR V grain recording density Conflicting Requirements THERMAL STABILITY Slide 20

21 Signal to Noise Ratio (SNR) Longitudinal Recording Perpendicular Recording Future Perspectives Reliable detection of stored data SNR > 25 db 5 nm c-axis The in plane size of the grains (D) has been continuously reduced as higher recording densities were achieved D D Slide 21

22 Signal to Noise Ratio (SNR) Longitudinal Recording Perpendicular Recording Future Perspectives Reliable detection of stored data SNR > 25 db 5 nm c-axis The in plane size of the grains (D) has been continuously reduced as higher recording densities were achieved SNR can be improved by reducing the randomness in the nature of grains reduction of the dispersion in easy axis orientation Direction of film thickness Cr-based underlayer promotes the parallel orientation of the c-axis (easy axis) of the HCP unit cell. Mechanical texturing process of the substrate allows partially orienting the easy axis along the track direction. Track direction Slide 22

23 Signal to Noise Ratio (SNR) Width of read head Longitudinal Recording Perpendicular Recording Future Perspectives Intended transition transition parameter Bit length (B) l Real transition D δ TRANSITION LENGTH Q = constant related to the head geometry d = head-medium separation Magnetic layer parameters M r = remanent moment δ = thickness D = in-plane grain size σ = grain size distribution M r δ = magnetic thickness Slide 23

24 Signal to Noise Ratio (SNR) Width of read head Longitudinal Recording Perpendicular Recording Future Perspectives Intended transition transition parameter Bit length (B) l Real transition D δ TRANSITION LENGTH Q = constant related to the head geometry d = head-medium separation Magnetic layer parameters M r = remanent moment δ = thickness D = in-plane grain size σ = grain size distribution M r δ = magnetic thickness Bit length (B) Wider transition D δ Bit length (B) l D δ Slide 24

25 Signal to Noise Ratio (SNR) Width of read head Longitudinal Recording Perpendicular Recording Future Perspectives Intended transition transition parameter Bit length (B) l Real transition D δ TRANSITION LENGTH Q = constant related to the head geometry d = head-medium separation Magnetic layer parameters M r = remanent moment δ = thickness D = in-plane grain size σ = grain size distribution M r δ = magnetic thickness Bit length (B) Wider transition D δ Bit length (B) l D δ Slide 25

26 Signal to Noise Ratio (SNR) Width of read head Longitudinal Recording Perpendicular Recording Future Perspectives Intended transition transition parameter Bit length (B) l Real transition D δ TRANSITION LENGTH Q = constant related to the head geometry d = head-medium separation Magnetic layer parameters M r = remanent moment δ = thickness D = in-plane grain size σ = grain size distribution M r δ = magnetic thickness Grain volume Bit length (B) Wider transition D δ Bit length (B) l D δ Slide 26

27 Thermal Stability Longitudinal Recording Perpendicular Recording Future Perspectives Longitudinal recording media can be approximated to a 2D isotropic Stoner- Wohlfarth system. FIELD ACTIVATED SWITCHING THERMAL ACTIVATED SWITCHING Mean reversal time H 2 > H 1 H 1 H 2 Slide 27

28 Write-ability Longitudinal Recording Perpendicular Recording Future Perspectives The reduction of V grain can be counterbalanced by increasing K u of the magnetic layer Using materials high K u is limited by the write field (H x ) Recording Medium Material k u (10 7 erg/cm 3 ) CoCrPtX k u Pt, Cr Co/Pt(Pd) ~1 Co 3 Pt 0.6 L1 0 CoPt 5 L1 0 FePt 7 Write Head Material µ max (10 3 ) 4πM s (G) H c (Oe) Fe Recording Medium d = 20 nm in 2006 Fe 49 Co 49 V δ Ni 50 Fe H x Ni 80 Fe 15 Mo Slide 28

29 Longitudinal Recording Antiferromagnetically-coupled (AFC) Media Perpendicular Recording Future Perspectives Areal Density [Gb/in 2 ] E-3 1E-4 1E-5 1E-6 10 Tb/in2 1 Tb/in Gb/in 2 1 Gb/in AFC Media 1997 GMR Read Head 1990 MR Read Head 1980 Thin Film WR Head 1 Mb/in RAMAC Longitudinal Recording 2006 Perp. Media TMR Read Head Year 2011 DEMO [Co/Pd] n BPM 1T/in 2 TERAMAGSTOR EU-Project? BPM, High K u Materials, HAMR, ESM, etc. Perpendicular Recording Top FM Layer Ru Layer (< 1 nm) Bottom FM Layer Ru thickness is tuned to antiferromagnetically couple the FM layers via RKKY interactions Smaller transition length Improved SNR can be increased Larger grain volume Improved thermal stability Slide 29

30 Hard Disk Drive Roadmap Longitudinal Recording Perpendicular Recording Future Perspectives Areal Density [Gb/in 2 ] E-3 1E-4 1E-5 1E-6 10 Tb/in2 1 Tb/in Gb/in 2 1 Gb/in AFC Media 1997 GMR Read Head 1990 MR Read Head 1980 Thin Film WR Head 1 Mb/in RAMAC 1975 Perpendicular recording was introduced Longitudinal Recording 2006 Perp. Media TMR Read Head Year 2011 DEMO [Co/Pd] n BPM 1T/in 2 TERAMAGSTOR EU-Project?? Perpendicular Recording BPM, High K u Materials, HAMR, ESM, etc. Slide 30

31 General Aspects Longitudinal Recording Perpendicular Recording Future Perspectives Slide 31

32 Write/Read Head Longitudinal Recording Perpendicular Recording Future Perspectives READ HEAD TUNNELING MAGNETORESISTIVE SPIN VALVE Mechanism Spin dependent tunneling Free layer Pinned layer FM FM AFM Insulating spacer (e.g. MgO) WRITE HEAD Single pole Head + SUL Guides the magnetic flux (Φ) from the write pole to the collector pole of the write head. Simple models assume that the SUL generates a mirror image of the write head The recording medium is placed in the gap of the write head Slide 32

33 Recording Medium Prepared by Dip-coating Prepared by Sputtering Lubricant Overcoat Recording layer Intermediate Layer Soft Underlayer (SUL) Adhesion layer Substrate Longitudinal Recording Perpendicular Recording Future Perspectives PFPE (~1 nm) Reduces friction and wear during the head-disk contact Diamond Like Carbon DLC (~1 nm) Provides chemical and mechanical protection Ru (20 nm) Exchange-decouples the SUL and the magnetic layer Favours the epitaxial growth of the magnetic layer CoTaZn amorphous ( nm) Helps in conducting the flux form the write pole of the head and the connector pole Al, Ti (10 nm) Improve the adhesion of SUL Al-Alloy, Glass Performs the role of support (hard, stiff, inert, smooth Core: Co-rich (magnetic) Boundary: SiO 2 (non-magnetic) MAGNETIC LAYER CoCrPt@SiO 2 (15nm) SiO 2 : enhances grain isolation (allows reducing Cr content K u ) Granular (<size> = 6 nm) easy-axis CoCrPt@SiO 2 Smooth surface (roughness < 5 nm rms) Stoner-Wohlfarth like system Single domain grains Weakly exchange coupled grains Uniaxial perpendicular anisotropy K u Slide 33

34 Advantages Longitudinal Media Longitudinal Recording Perpendicular Recording Future Perspectives MEDIA ALIGNMENT Perpendicular Media Random easy-axis orientation 2 Improved SNR Uniform easy axis orientation RECORDING FIELD Writing is performed by the fringe fields. The recording medium is placed in the gap of the write head H write PRM 2 H write LRM Improved write-ability Material with higher K u can be used Improved Thermal Stability STRAY FIELD AT BIT BOUNDARY δ δ Ultra narrow transition Improved SNR Higher M r δ can be used Improved thermal stability Slide 34

35 Advantages Longitudinal Media Longitudinal Recording Perpendicular Recording Future Perspectives MEDIA ALIGNMENT Perpendicular Media Random easy-axis orientation 2 Improved SNR Uniform easy axis orientation RECORDING FIELD Writing is performed by the fringe fields. The recording medium is placed in the gap of the write head H write PRM 2 H write LRM Improved write-ability Material with higher K u can be used Improved Thermal Stability STRAY FIELD AT BIT BOUNDARY δ δ Destabilizing stray fields deep inside the bit A smaller amount of intergranular interaction is desired to reduce the destabilizing effects. Slide 35

36 Alternative Materials and Novel Concepts Longitudinal Recording Perpendicular Recording Future Perspectives Areal Density [Gb/in 2 ] E-3 1E-4 1E-5 1E-6 10 Tb/in2 1 Tb/in Gb/in 2 1 Gb/in AFC Media 1997 GMR Read Head 1990 MR Read Head 1980 Thin Film WR Head 1 Mb/in 2 Longitudinal Recording 1956 IBM RAMAC (first HDD, 2 Kb/in 2 ) 2006 Perp. Media TMR Read Head 2011 DEMO [Co/Pd]n BPM - 1 Tb/in 2 TERAMAGSTOR EU-Project Year? Perpendicular Recording SOLUTIONS Areal density > 600 Gb/in 2 ( D grain V grain ) CoCrPt@SiO 2 media could face a thermal instability problem Material k u (10 7 erg/cm 3 ) Co/Pt(Pd) ~1 L1 0 CoPt 5 L1 0 FePt 7 Novel concepts to combine thermal stability and write-ability issues Heat assisted magnetic recording Tilted media Exchange-spring media Patterned Media Bit patterned media One dot - One bit K u V is not longer governed by V grain but rather by the V dot Slide 36

37 Heat Assisted Magnetic Recording - HAMR Longitudinal Recording Perpendicular Recording Future Perspectives WRITING PROCESS A tightly focused laser beam is used to increase the medium temperature up to a value where the anisotropy of the medium is low and thus only a very small field is required to switch the media. Higher K u materials can be used Improved thermal stability READ-OUT PROCESS Is performed with a magnetoresistive head at room temperature MAIN CHALLENGES Near field optics are required to make the heat spot small enough to avoid thermal erasure of the adjacent tracks. Recording medium and head need to have adequate thermal properties. New materials for lubricant layer are necessary to avoid thermal deterioration. M. Kryder, Proc. IEEE Slide 37

38 Tilted Media Longitudinal Recording Perpendicular Recording Future Perspectives STONER-WOHLFARTH SYSTEM 2/3 2/3 3/ 2 [(cos α) + (sin ) ] H sw = H k α Η z α Normalized Switching Field H sw / H K EA Conventional perpendicular writing Tilted perpendicular writing H sw α ( ) ( α = 45 ) = 0.5( α = 0 ) J. Wang, Nature Mat y Recording medium plane Higher K u materials can be used Improved thermal stability Slide 38 x

39 Exchange Spring Media - ESM Longitudinal Recording Perpendicular Recording Future Perspectives Soft Hard H sw of an extremely hard magnetic layer can be reduced by coupling with a softer magnetic film without affecting thermal stability. H n < H p H n > H p Soft H sw = max(h p,h n ) Hard A. H = H n ; a wall nucleates in the soft layer. B.C. The wall propagates to the soft-hard interface where it becomes pinned. With increasing H the domain wall becomes compressed. D.E. H = H p ; the bilayer completely reverses. ( K K ) 2 hard soft H 1 p ( ) 2 µ M + M K hard A 0 µ hard s, hard 0 s, soft A = exchange stiffness The expression is valid if both layers are thick enough to fit a full domain wall K soft A soft Reversible reversal perpendicular D. Suess et al., JMMM Slide 39

40 Exchange Spring Media - ESM Longitudinal Recording Perpendicular Recording Future Perspectives Soft Hard H sw of an extremely hard magnetic layer can be reduced by coupling with a softer magnetic film without affecting thermal stability. H n < H p H n > H p Soft H sw = max(h p,h n ) Hard A. H = H n ; a wall nucleates in the soft layer. B.C. The wall propagates to the soft-hard interface where it becomes pinned. With increasing H the domain wall becomes compressed. D.E. H = H p ; the bilayer completely reverses. ( K K ) 2 hard soft H 1 p ( ) 2 µ M + M K hard A 0 µ hard s, hard 0 s, soft A = exchange stiffness The expression is valid if both layers are thick enough to fit a full domain wall K soft A soft Reversible reversal K u perpendicular GRADED MEDIA Allow further reduction of H sw Graded Hard t G H sw 2 µ M 0 s AK t G hard D. Suess et al., JMMM Slide 40

41 Bit Patterned Media - BPM Longitudinal Recording Perpendicular Recording Future Perspectives MAIN CHALLENGE Extreme fabrication requirements (low cost, high resolution, large area order) Density (Tb/in 2 ) Bit period (nm) BAR= Potential way: E-beam lithography + nano-imprinting One e-beam master template CONVENTIONAL MEDIA Continuous granular recording media Multiple grains per bit Boundaries between bits determined by grains Thermal stability unit is one grain BIT PATTERNED MEDIA Highly exchange coupled granular media Multiple grains per island, but each island is a single domain particle Bit locations determined by lithography Thermal stability unit is one dot Improved thermal stability nanoimprint stampers imprinted disks Slide 41

42 Final Remarks Current HDDs Perpendicular Mode Recording Density: 600 Gb/in 2 HDD sold in 2010: 700 million Cost/Gb: 0.02 $ Emerging technologies for magnetic information storage Race Track Memory Magnetic Random Access Memory (MRAM) Slide 42

43 Recommended readings BOOKS Piramanayagam S N and Chong T C (editors), Developments in data storage, John Wiley & Sons 2011 Khizroev S and Litvinov D (editors), Perpendicular magnetic recording, Kluwer Academic 2009 Hadjipanyis G (editor), Magnetic Storage Systems Beyond 2000, Kluwer Academic Press 2000 Plumer M L, van Eck J and Weller D (editors), The physics of ultra-high density magnetic recording, Springer 1999 REVIEWS Piramanayagam S N et al., Recording media research for future hard disk drives, Journal of Magnetism and Magnetic Materials Parkin S S P et al., Magnetic domain-wall racetrack memory, Science Piramanayagam S N, Perpendicular recording media for hard disk drives, Journal of Applied Physics Richter H J, The transition from longitudinal to perpendicular recording, Journal of Physics D: Applied Physics 40 R Richter H J et al., Media for magnetic recording beyond 100 Gbit/in 2, MRS Bulletin McFadyen I R et al., State-of-the-art magnetic hard disk drives, MRS Bulletin Comstock R L, Modern magnetic materials in data storage, Journal of Materials Science: Materials in Electronics Moser A et al., Magnetic recording: advancing into the future, Journal of Physics D: Applied Physics 35 R Richter H J, Recent advances in the recording physics of thin-film media Journal of Physics D: Applied Physics 32 R Slide 43

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