Magnetic Memory:Data Storage and Nanomagnets

Magnetic Memory:Data Storage and Nanomagnets

Mark Tuominen Professor of Physics

10 GB2001

20 GB2002

40 GB2004

80 GB2006

160 GB2007

Data Storage. Example: Advancement of the iPod

Hard driveMagnetic data storage

Uses nanotechnology!

Review

Ferromagnetuniform magnetization

anisotropy axis("easy" axis)

Electron magnetic moments ("spins")

Aligned by "exchange interaction"

Bistable:Equivalentenergy for "up" or "down"states

Ferromagnets are used to store data

?

Ferromagnet with unknown magnetic state

Current

N

S

‘0’

S

Current

N

‘1’

Magnetic Data StorageA computer hard drive stores your data magnetically

Disk

N S

direction of disk motion

“ Write”Head

0 0 1 0 1 0 0 1 1 0 _ _

“ Bits” ofinformation

NS

“ Read”Head

Signalcurrent

Scaling Down to the Nanoscale

Increases the amount of data stored on a fixed amount of “real estate” !

Now ~ 100 billion bits/in2, future target more than 1 trillion bits/in2

25 DVDs on a disk the size of a quarter.

Improving Magnetic Data Storage Technology

• The UMass Amherst Center for Hierarchical Manufacturing is working to improve this technology

Granular Media

PerpendicularWrite Head

Soft Magnetic UnderLayer (SUL)

coil

Y. Sonobe, et al., JMMM (2006)

1 bit

• CHM Goal: Make "perfect" mediausing self-assembled nano-templates• Also, making new designs for storage

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Filling the Template: Making Cobalt Nanorods by Electrochemical

Deposition

WE REF

electrolyte

CE

Co2+

Co

metal

Binary Representation of Data

one bit “ 1” or “0” only 2 choices

two bits 00, 01, 10, 11 4 choices

three bits 000, 001, 010, 011,100, 101, 110, 111

8 choices

n bits has 2n choices

For example, 5 bits has 25 = 32 choices...more than enough to represent all the letters of the alphabet

Character "SS"codea 00001b 00010c 00011d 00100e 00101f 00110g 00111h 01000i 01001j 01010k 01011l 01100

m 01101n 01110o 01111p 10000q 10001r 10010s 10011t 10100u 10101v 10110w 10111x 11000y 11001z 11010

Binary representationof lower case letters

5-bit "Super Scientist" code:

ex: k = 01011

0 1 0 1 1

S

N

S

N

S

N

N

S

N

S

OR

(Coding Activity: Use attractive and repulsive forces to "read" the magnetic data!)

NEW! Multi-State Representation of Data

Disk

“ Write”Head

“ Read”Head

= =0 1

direction of disk motion

1 0 3 2

0

12

3

"CLUSTERS"

M = -3 M = -1 M = +1 M = +3

3-Nanomagnet ClusterImaged with a MFM

(Magnetic Force Microscope)

Just accomplished summer 2007 in the CHM!

Character "SS"codea 001b 002c 003d 010e 011f 012g 013h 020i 021j 022k 023l 030

m 031n 032o 033p 100q 101r 102s 103t 110u 111v 112w 113x 120y 121z 122

"Multi-state" representationof lower case letters

— — — — — —

10 32

What is the word?

The Bistable Magnetization of a Nanomagnet• A single-domain nanomagnet with a

single “easy axis” (uniaxial anisotropy) has two stable magnetization states

“topview”shorthand

zor H

Mz Mz

Mz

H

Bistable. Ideal for storing data - in principle, even one nanomagnet per bit.

hysteresis curve

E = K1sin2•H switching field