1. C D Wright and M K Loze Department of Engineering University of Exeter, UK An effective-field approach to understanding MAMMOS behaviour Acknowledgement - EU FP5 funding via MAMMOSIL project Project partners: LETI-CEA, MPO, Thomson, Unaxis-Nimbus, TuiOptics

2. MAMMOS Performance Prospects = 650 nm, NA = 0.6 50nm mark, 100nm space 0.4  m L/G recording 20 Gbit/sq.in 30GBytes CD-size disc = 400 nm, NA = 0.6 50 Gbit/sq.in 75GBytes CD-size disc = 400 nm, NA = 085 100 Gbit/sq.in 150GBytes CD-size disc = 400 nm, SIL, NA~1.4 300 Gbit/sq.in 450GBytes CD-size disc Source Awano et al ISOM/ODS 1999 MORIS 2004 results 52Gbits/sq.in first surface ZF-MAMMOS, 100Mbps - Hitachi and Fujitsu Double-MAMMOS with 2 x storage layer/single readout layer for 100Gbit/sq.in.

3. Which MAMMOS technique ? Readout Field Zero Constant (DC) Modulated (AC) Magnetic Coupling Exchange Magnetostatic Readout Layer In-plane anisotropy Perpendicular anisotropy Initial MAMMOSIL choice AC MAMMOS Magnetostatic coupling Perpendicular anisotropy readout layer

4. AC - MAMMOS with perpendicular readout layer H read

5. Laser Heating: MAMMOS-type Disk Disk structure Power density Heat generation rate Temperature distribution through the disk Temperature distributions along the track Cover layer or substrate Substrate/protection layer

6. Effective Field Model Nucleation Model Nucleation of a readout layer domain requires H read : Readout field. H d : Readout layer demagnetizing field. H z : Magnetostatic copy field due to the record layer mark. H cn : Nucleation coercivity. H nucl : Nucleation-resisting field. Domain Expansion Model Expansion of the readout layer domain requires H cw : Wall-motion coercivity. H wall : Wall-motion-resisting field.

7. Two-Coercivity Model

8. AC MAMMOS with RE-Rich Readout Layer An RE-rich readout layer with T comp above room temperarture used (360K here) Region below T comp forms a mask (RE-rich zone) Region above T comp constitutes an aperture (TM-rich zone) into which the record layer mark is copied under an external field. Copied domain then (ideally) expands to fill the aperture. Readout signal amplitude for this type of readout layer is limited by the aperture size

9. Static Readout of Isolated 50 nm Circular Marks Stable domain radii in the Disk Operating Region (DOR). Record layer: T comp = 290 K, M s (T peak ) = 50 emu/cc, R = 50 nm. Readout layer: RE-rich with [ ,  ] = [ 0.15, 0.2 ].

10. Copy field and resolution 50 nm radius marks 100 nm spaces Blue laser focused on central mark and central space Field parameters H 1, H 2. H 3, H 4 and  H 13 (defined as H 1 -H 3 ) (normalized w.r.t. M s (T peak )) are defined opposite. The plot shows H z / M s (T peak ) along the track centre-line when the laser is focused on a mark (red) a space (blue)

11. Disk Operational Region for H 1 = 2 and  H 13 = 0.25 and 0.5. Copy field resolution - effect on DOR

12. Readout of Circular Marks: Movies Multiple pulse response Output follows readout field Blue circle: Laser spot (1/e radius). Red circle: Readout aperture. Green: Recorded marks. Red: Readout domains. Missing pulses Correct operation

13. Readout of Circular Marks: Performance Above: System performance as a function of ( P read, H read ). Right: Close-up of the system performance with contours of A read / A rec shown.

14. Readout of Crescent Marks: Movies Blue circle: Laser spot (1/e radius). Red circle: Readout aperture. Green: Recorded marks. Red: Readout domains. Left: All marks are resolved. Closely spaced marks are not expanded. Right: All marks are resolved and expanded by a factor of about 2.

15. Choosing the right readout layer properties Look at role of readout layer compensation temperature T comp = 360K +  T comp

16. Readout of Circular Marks: Varying Readout Power Above: System performance as a function of (  T comp, P read ) for H read = 100 Oe. Right: Readout power margin,  P read, and A read /A rec versus  T comp for H read = 100 Oe.

17. Readout of Circular Marks: Varying Readout Field Above: System performance as a function of (  T comp, H read ) for P read = P read(max) Right: The readout field margin,  H read, and A read /A rec, versus  T comp for P read(max)

18. Can we implement Zero-Field MAMMOS with this disk ?

19. ZF-MAMMOS: Basics ZF readout aperture

20. ZF-MAMMOS Disk: Readout Layer Magnetic Properties

21. ZF-MAMMOS: Isolated Crescent Right : The readout domain size (normalized w.r.t. the aperture area) as the laser beam scans across the isolated crescent. Left : Correct operation of ZF- MAMMOS readout.

22. ZF-MAMMOS: Packed Crescents Above : ZF-MAMMOS operation for a series of 12 100 nm crescent-shaped marks with 200 nm spaces. Right : The readout domain size (normalized w.r.t. the aperture area) as the laser beam scans across the series of crescents. Note that the first mark is not detected.

23. Conclusions A thermo-magnetic effective field model has been developed to: aid the magnetic & physical design of AC and ZF MAMMOS disks predict disk operating margins for AC and ZF MAMMOS predict readout and recording behaviour Method is adaptable to other MO formats and also to HAMR ?