C D Wright and M K Loze Department of Engineering University of Exeter, UK

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

2. MAMMOS Performance Prospects Source Awano et al ISOM/ODS 1999  = 650 nm, NA = 0.6 50nm mark, 100nm space 0.4m L/G recording 20 Gbit/sq.in 30GBytes CD-size disc 50 Gbit/sq.in 75GBytes CD-size disc  = 400 nm, NA = 0.6 100 Gbit/sq.in 150GBytes CD-size disc  = 400 nm, NA = 085 300 Gbit/sq.in 450GBytes CD-size disc  = 400 nm, SIL, NA~1.4 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 Layer In-plane anisotropy Perpendicular anisotropy Magnetic Coupling Exchange Magnetostatic Readout Field Zero Constant (DC) Modulated (AC) Initial MAMMOSIL choice AC MAMMOS Magnetostatic coupling Perpendicular anisotropy readout layer

4. AC - MAMMOS with perpendicular readout layer Hread

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

6. Effective Field Model • Nucleation Model • Nucleation of a readout layer domain requires • Hread : Readout field. • Hd : Readout layer demagnetizing field. • Hz: Magnetostatic copy field due to the record layer mark. • Hcn: Nucleation coercivity. • Hnucl: Nucleation-resisting field. • Domain Expansion Model • Expansion of the readout layer domain requires • Hcw : Wall-motion coercivity. • Hwall: Wall-motion-resisting field.

7. Two-Coercivity Model

8. AC MAMMOS with RE-Rich Readout Layer An RE-rich readout layer with Tcomp above room temperarture used (360K here) Region below Tcomp forms a mask (RE-rich zone) Region above Tcomp 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. Stable domain radii in the Disk Operating Region (DOR). Record layer: Tcomp= 290 K, Ms(Tpeak) = 50 emu/cc, R = 50 nm. Readout layer: RE-rich with [  ,  ] = [ 0.15 , 0.2 ]. Static Readout of Isolated 50 nm Circular Marks

10. Copy field and resolution 50 nm radius marks 100 nm spaces Blue laser focused on central mark and central space Field parameters H1, H2. H3, H4 andH13 (defined as H1-H3) (normalized w.r.t. Ms(Tpeak)) are defined opposite. The plot shows Hz / Ms(Tpeak) along the track centre-line when the laser is focused on a mark (red) a space (blue)

11. Copy field resolution - effect on DOR Disk Operational Region for H1 = 2 and H13 = 0.25 and 0.5.

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

13. Above: System performance as a function of ( Pread , Hread ). Right: Close-up of the system performance with contours of Aread / Arec shown. Readout of Circular Marks: Performance

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

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

16. Readout of Circular Marks: Varying Readout Power Above: System performance as a function of ( Tcomp , Pread ) for Hread = 100 Oe. Right: Readout power margin, Pread, and Aread/Arec versus Tcomp for Hread = 100 Oe.

17. Readout of Circular Marks: Varying Readout Field Above: System performance as a function of ( Tcomp , Hread ) for Pread = Pread(max) Right: The readout field margin, Hread, and Aread/Arec, versus Tcomp for Pread(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 Left : Correct operation of ZF-MAMMOS readout. Right : The readout domain size (normalized w.r.t. the aperture area) as the laser beam scans across the isolated crescent.

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 ?