c d wright and m k loze department of engineering university of exeter, uk
DESCRIPTION
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. MAMMOS Performance Prospects. - PowerPoint PPT PresentationTRANSCRIPT
C D Wright and M K LozeDepartment of Engineering
University of Exeter, UK
An effective-field approach to understanding MAMMOS behaviour
Acknowledgement - EU FP5 funding via MAMMOSIL projectProject partners: LETI-CEA, MPO, Thomson, Unaxis-Nimbus, TuiOptics
MAMMOS Performance Prospects
= 650 nm, NA = 0.6 50nm mark, 100nm space0.4m 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.
Which MAMMOS technique ?
Readout Field
Zero
Constant (DC)
Modulated (AC)
Magnetic Coupling
Exchange
Magnetostatic
Readout Layer
In-plane anisotropy
Perpendicular anisotropy
Initial MAMMOSIL choiceAC MAMMOS
Magnetostatic couplingPerpendicular anisotropy readout
layer
Readout layer
Record layer
Nucleation
Dielectric layer
Readout layer
Record layer
Initial Disk Magnetization
Dielectric layerReadout layer
Record layer
Initial Disk Magnetization
Dielectric layer
Readout layer
Record layer
Nucleation
Dielectric layer
Readout layer
Record layer
Domain Copying
Dielectric layer
Readout layer
Record layer
Domain Expansion
Dielectric layer
Readout layer
Record layer
Domain Collapse
Dielectric layer
Above: Readout layer domain nucleation inthe absence of a record layer mark. Thissituation must be avoided for correctMAMMOS disk operation.
Right: Readout layer domain nucleation,copying, expansion and collapse in thepresence of a record layer mark. Thissituation is required for correct MAMMOSdisk operation
AC - MAMMOS with perpendicular readout layer
Hread
Laser Heating: MAMMOS-type Disk
Disk structurePower density
Heat generation rate
Temperature distribution through the disk
Temperature distributions along the track
Data for the MAMMOS-type diskDescription of the layer Thickness
(nm) Refractive Index at 405 nm
Conductivity J/ (m s °C )
Density*Heat Capacity MJ/ (m³ °C )
Polycarbonate substrate Thick 1.58 0.2 1.5Si3N4 dielectric 60 2 2 2.4GdFeCo readout 20 2.1 – j 2.7 6 3Si3N4 dielectric 5 2 2 2.4TbFeCoCr record 50 1 .63 – j 2.21 10 3Si3N4 dielectric 20 2 2 2.4Al alloy 30 0.5 – j 5 50 2.4UV-cured protection Thick 1.55 0.2 1.8
Cover layer or substrate
Substrate/protection layer
Effective Field Model Nucleation ModelNucleation 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 ModelExpansion of the readout layer domain requires
• Hcw : Wall-motion coercivity. • Hwall : Wall-motion-resisting field.
nuclcnzdread HHHHH
wallcwzdread HHHHH
Two-Coercivity Model
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
Static Readout of Isolated 50 nm Circular Marks
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 ].
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)
Disk Operational Region for H1 = 2 and H13 = 0.25 and 0.5.
Copy field resolution - effect on DOR
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
Readout of Circular Marks: Performance
Above: System performance as a function of ( Pread , Hread ).
Right: Close-up of the system performance with contours of Aread / Arec shown.
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.
Choosing the right readout layer properties
Look at role of readout layer compensation temperatureTcomp = 360K + Tcomp
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.
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)
Can we implement Zero-Field MAMMOS with this disk ?
ZF-MAMMOS: Basics
ZF readout aperture
ZF-MAMMOS Disk: Readout Layer Magnetic Properties
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.
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.
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 ?