C D Wright and M K Loze

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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
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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, NA1.4
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.
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Which MAMMOS technique ?
Magnetic Coupling Exchange Magnetostatic
Readout Layer In-plane anisotropy Perpendicular
anisotropy
Readout Field Zero Constant (DC) Modulated (AC)
Initial MAMMOSIL choice AC MAMMOS Magnetostatic
coupling Perpendicular anisotropy readout layer
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AC - MAMMOS with perpendicular readout layer
Hread
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Laser Heating MAMMOS-type Disk
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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.

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Two-Coercivity Model
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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
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Static Readout of Isolated 50 nm Circular Marks
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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)
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Copy field resolution - effect on DOR
Disk Operational Region for H1 2 and ?H13
0.25 and 0.5.
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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.
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Readout of Circular Marks Performance
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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.

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Choosing the right readout layer properties
Look at role of readout layer compensation
temperature
Tcomp 360K ?Tcomp
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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.
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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)
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Can we implement Zero-Field MAMMOS with this disk
?
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ZF-MAMMOS Basics
ZF readout aperture
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ZF-MAMMOS Disk Readout Layer Magnetic Properties
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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.
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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.
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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 ?