Future Magnetic Storage Media
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Future Magnetic Storage Media Jim Miles Electronic and Information Storage Systems Research Group PowerPoint PPT Presentation


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Future Magnetic Storage Media Jim Miles Electronic and Information Storage Systems Research Group. Media requirements for very high density Model description Predicted effects of grain size distribution Patterned media: possible routes Conclusions. Future Magnetic Storage Media.

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Future Magnetic Storage Media Jim Miles Electronic and Information Storage Systems Research Group

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Future magnetic storage media jim miles electronic and information storage systems research group

Future Magnetic Storage Media

Jim Miles

Electronic and Information Storage Systems Research Group


Future magnetic storage media

Media requirements for very high density

Model description

Predicted effects of grain size distribution

Patterned media: possible routes

Conclusions

Future MagneticStorage Media


Granular or patterned media

Granular or Patterned Media?


Future magnetic storage media jim miles electronic and information storage systems research group

Thetransition from one bit to another follows the grains…

(or maybe clusters of grains).

Jitter

Small grains are needed for low noise.

W

D

Granular Media Limitations


Writing to media

Field H > HK = 2KU

0MS

Writing to Media

A sufficiently large field is needed to overcome the anisotropy of the material, which keeps magnetisation aligned along one axis

Anisotropy Ku

Magnetisation MS


Thermal stability of media

Energy barrier EB = KUV

Thermal energy ~ KBT

Spontaneous switching

when EB < 70KBT

Require EB ~70 KBT

Thermal Stability of Media


To increase the density

To Increase the Density:

  • Decrease the bit length: Jitter must decrease

  • Decrease the track width W: Jitter must not increase.

  • Jitter ,  grain diameter D must fall

  • Volume V = D2t/4  Volume falls

  •  KU must rise to keep EB = KUV high enough

  •  bigger write field H > 2KU/0MS is needed.

  • Density can only rise by increasing write field.


Perpendicular recording

Perpendicular Recording

Increases write field, but only by ~ x2…


Other problems of granular media

Media are granular.

Grains are not equal-sized.

Typically D ~ 0.2<D>, V ~ 0.4<V>

Hypothesis - Irregularity in media structure produces noise:

Big grains give big transition deviations;

Different grain volumes switch more or less easily;

Different grains see different local interaction fields.

Other Problems of Granular Media


Perpendicular media modelling

Perpendicular Media Modelling

Real Storage Medium Model Storage Medium

(not to identical scale)


Future magnetic storage media jim miles electronic and information storage systems research group

Manchester MicroMagnetic Multilayer Media Model (M6)

Mmmmmm...

  • Landau-Lifshitz dynamic and M-C thermal solvers.

  • Arbitrary sequences of uniform vector applied fields

  • Recording simulation with FEM or analytical head fields.

  • Soft underlayer by perfect imaging

  • Microstructural clustering and texturing.

  • Fully arbitrary grain positions and shapes.

  • Full account of grain shape in interaction fields

  • Allows vertical sub-division and tilted columns (MET like)


Future magnetic storage media jim miles electronic and information storage systems research group

Hj

Mi

Magnetostatic Interaction - Pairs of Grains

Interaction Field: Hj = DijMi

Magnetostatic interaction tensors D are computed numerically

‘Field’ grain experiences a field that varies through the volume.

Surface charge from each polygon face of the source generates field. Typically 48 faces per polygon.

Top and bottom faces computed similarly by division into strips.

Integrate over the surface charge of i and the volume of j.

Underlayer included by incorporating images into Dij


Future magnetic storage media jim miles electronic and information storage systems research group

x

j (field)

dij

dij

x

i (source)

Exchange Interaction - Pairs of Grains

Exchange interaction factors are computed numerically

Grain j experiences an exchange field due to grain i

Integral term computed numerically from polygon geometry


Future magnetic storage media jim miles electronic and information storage systems research group

Varying Grain Size

  • Voronoi seed positions randomised

  • Minimum grain boundary width 0.7nm fixed

  • Number of grains/m2 and packing fraction fixed

  • Mean grain volume remains constant

  •  Hex remains constant

σv/<v> = 0% σv/<v> = 15% σv/<v> = 39%


Future magnetic storage media jim miles electronic and information storage systems research group

Grain Size Distributions

σv/<v> = 0%σv/<v> = 4.7%σv/<v> = 10.2%σv/<v> = 15.5%σv/<v> = 22.6%σv/<v> = 29.4%σv/<v> = 38.7%


Future magnetic storage media jim miles electronic and information storage systems research group

100

80

% of grains

60

40

20

0

0.6

0.8

1

1.2

1.4

Hey/<He>

Exchange Field Distributions

Average exchange field does not change as the microstructure changes.

HE = 0.5 HD

A = 1.85x10-13

for all structures

σv/<v> = 0%σv/<v> = 4.7%σv/<v> = 10.2%σv/<v> = 15.5%σv/<v> = 22.6%σv/<v> = 29.4%σv/<v> = 38.7%


Future magnetic storage media jim miles electronic and information storage systems research group

Exchange Interaction Between Pairs of Grains Width of line  Hex

Uniform grains, perfect hexagonal lattice. Exchange field is identical between all pairs.

Thermally decayed from DC saturated

σv/<v> = 0

HE/HD = 0.5


Future magnetic storage media jim miles electronic and information storage systems research group

Exchange Interaction Between Pairs of GrainsWidth of line  Hex

Large volume distribution:

σv/<v> = 39%

Irregular structure, Large variation in HE

<HE>/<HD> = 0.5


Future magnetic storage media jim miles electronic and information storage systems research group

Magnetostatic (Demag) Field Distributions

σv/<v> = 0%σv/<v> = 4.7%σv/<v> = 10.2%σv/<v> = 15.5%σv/<v> = 22.6%σv/<v> = 29.4%σv/<v> = 38.7%


Future magnetic storage media jim miles electronic and information storage systems research group

Energy Barrier Distributions

σv/<v> = 0%σv/<v> = 4.7%σv/<v> = 10.2%σv/<v> = 15.5%σv/<v> = 22.6%σv/<v> = 29.4%σv/<v> = 38.7%


Future magnetic storage media jim miles electronic and information storage systems research group

Recorded Transitions, b=20nm, Tp = 80nm, 411 Gb/in2

σv/<v> = 39%

σv/<v> = 0%


Future magnetic storage media jim miles electronic and information storage systems research group

0.5

0.45

0.4

0.35

Fundmamental/Ms

0.3

0.25

0.2

0.15

1

1.5

2

2.5

3

3.5

4

kfrci

6

x 10

Effect of Irregularity on Data Signal

σv/<v> = 0%σv/<v> = 4.7%σv/<v> = 10.2%σv/<v> = 15.5%σv/<v> = 22.6%σv/<v> = 29.4%σv/<v> = 38.7%


Future magnetic storage media jim miles electronic and information storage systems research group

Effect of Irregularity on Noise

σv/<v> = 0%σv/<v> = 4.7%σv/<v> = 10.2%σv/<v> = 15.5%σv/<v> = 22.6%σv/<v> = 29.4%σv/<v> = 38.7%


Grain microstructure conclusions

Grain size distributions give rise to decreased signal and increased noise (BAD)

Media with small grain size distributions are needed

Patterned media are needed

Additional advantage: switching volume is the bit size, not the grain size  lower switching field is possible.

Grain Microstructure Conclusions


Future magnetic storage media jim miles electronic and information storage systems research group

Tom Thomson


Future magnetic storage media jim miles electronic and information storage systems research group

Tom Thomson


Direct write e beam

Direct Write e-beam

  • Form master by direct write e-beam on resist layer

  • Evaporate gold coating

  • Lift-off gold from unexposed areas

  • Etch to remove magnetic layer except where protected by gold

50 nm diameter islands

B. Belle et. al.

University of Manchester


Patterned media potential

Provides a route to regular arrays of thermally stable low noise

1Tb/in2 requires 12.5nm lithography

Not feasible using semiconductor manufacturing technology for some years to come…

Patterned Media Potential


Self organised magnetic assembly soma media

FePt nanoparticles manufactured in aqueous suspension.

Very narrow size distribution.

Deposited onto substrate.

Self-Assemble into ordered structure.

Self-Organised Magnetic Assembly (SOMA Media)


Fept particle growth

FePt Particle Growth


Fept problems

FePt problems

FePt manufactured in solution has low Ku.

Very high Ku can be developed by annealing:

Much ongoing research in low temperature formation of high coercivity FePt…


Other potential technologies

Other Potential Technologies

Electro-chemical deposition in self-ordered templates: University of Southampton.

Electroplating into self-ordered pores in Alumite: R. Pollard et. al, Queens University Belfast.

Vacuum deposition through self-assembled nanosphere templates: Paul Nutter, Ernie Hill, University of Manchester.


Future magnetic storage media jim miles electronic and information storage systems research group

Self-Assembly – Long Range Order

Self-assembly produces only local order. Over long ranges order breaks down at dislocations.

Self-assembled pattern using a diblock co-polymer (in nanoimprinted grooves.

(C. Ross et al, MIT, 2002)

40nm diameter CoCrPt nanoparticles. Mask made from a diblock co-polymer (polystyrene/PMMA), self-assembled in nanoimprinted grooves.

(Naito et al, Toshiba, IEEE Trans. Magn 38 (5) (2002)


Conclusions

Conventional media can only be extended so far.

Patterned media overcome thermal stability issues.

Higher stability granular materials could be used with heat assisted recording (HAMR)

…but patterned media might still be needed to avoid excessive transition noise.

Patterned media are likely to be necessary in ~5 years

Conclusions


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