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 ?