Magnetic Memory: Data Storage and Nanomagnets

Mark Tuominen

Professor of Physics

Review

Data Storage. Example: Advancement of the iPod 10 GB 2001 20 GB 2002 40 GB 2004 80 GB 2006 160 GB 2007 Hard drive

Magnetic data storage

Uses nanotechnology!

Ferromagnet

uniform magnetization Electron magnetic moments ("spins") Aligned by "exchange interaction"

anisotropy axis ("easy" axis)

Bistable: Equivalent energy for "up" or "down" states

The Bistable Magnetization of a Nanomagnet

• A single-domain nanomagnet with a single “easy axis” (uniaxial anisotropy) has two stable magnetization states z M z or M z H M z

hysteresis curve “topview” shorthand E = K 1 sin 2



•

H

H

switching field

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

Ferromagnets are used to store data

?

Ferromagnet with unknown magnetic state S Current ‘ 0’ N Current N ‘ 1’ S

Magnetic Data Storage

A computer hard drive stores your data magnetically “ Read” “ Write” Signal current

S N

Disk 0 0 1

N

0

S

1 0 0 1 1 direction of disk motion 0 _ _ “ Bits” of

Scaling Down to the Nanoscale

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

Now ~ 100 billion bits/in 2 , future target more than 1 trillion bits/in 2 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 coil 1 bit Perpendicular Write Head Granular Media Soft Magnetic UnderLayer (SUL)

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

• CHM Goal: Make "perfect" media using self-assembled nano-templates • Also, making new designs for storage QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.

Filling the Template: Making Cobalt Nanorods by Electrochemical Deposition

Co 2+

WE REF electrolyte CE

Co

metal

Binary Representation of Data

one bit two bits three bits “ 1” or “0” 00, 01, 10, 11 000, 001, 010, 011, 100, 101, 110, 111 n bits has 2 n choices only 2 choices 4 choices 8 choices For example, 5 bits has 2 5 = 32 choices...

more than enough to represent all the letters of the alphabet

0 S N

Binary representation of lower case letters

5-bit "Super Scientist" code: ex: k = 01011 1 N S 0

OR

S N 1 N S 1 N S

m n o p q r s t u v w x y z Character "SS"code a 00001 b c 00010 00011 d e f 00100 00101 00110 g h i j k l 00111 01000 01001 01010 01011 01100 01101 01110 01111 10000 10001 10010 10011 10100 10101 10110 10111 11000 11001 11010

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

NEW! Multi-State Representation of Data “ Read” "CLUSTERS" “ Write” 3 2 1 0 Disk 1 0 3 2 = 0 = 1 direction of disk motion

M = -3

3-Nanomagnet Cluster

Imaged with a MFM (Magnetic Force Microscope) M = -1 M = +1 M = +3 Accomplished in the CHM!

"Multi-state" representation of lower case letters

0 1 2 3

What is the word?

m n o p q r s t u v w x y z Character "SS"code a 001 b c 002 003 d e f 010 011 012 g h i j k l 013 020 021 022 023 030 031 032 033 100 101 102 103 110 111 112 113 120 121 122

— — — — — —