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
Mz
Mz
or
H
“topview”
shorthand
Mz
hysteresis curve
H
E = K1sin2
•H
switching field
Bistable. Ideal for storing data - in principle, even one
nanomagnet per bit.
Ferromagnets are used to store data
Current
S
‘0’
?
N
Ferromagnet with unknown
magnetic state
Current
N
‘1’
S
Magnetic Data Storage
A computer hard drive stores your data magnetically
“Read”
Head
“Write”
Head
Signal
S
N
N
S
0
1
current
Disk
0
0
1
0
0
1
direction of disk motion
1
0
_
_
“Bits” of
information
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
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
Co2+
electrolyte
WE
REF
CE
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
Binary representation
of lower case letters
Character "SS"code
5-bit "Super Scientist" code:
ex: k = 01011
1
0
1
1
S
N
OR
S
N
N
N
S
N
S
S
0
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
00001
00010
00011
00100
00101
00110
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
"CLUSTERS"
“Read”
Head
“Write”
Head
3
2
1
0
Disk
1
0
3
=
2
0
=
1
direction of disk motion
3-Nanomagnet Cluster
Imaged with a MFM
(Magnetic Force Microscope)
M = -3
M = -1
M = +1
Accomplished in the CHM!
M = +3
"Multi-state" representation
of lower case letters
0
1
2
3
What is the word?
——————
Character "SS"code
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
001
002
003
010
011
012
013
020
021
022
023
030
031
032
033
100
101
102
103
110
111
112
113
120
121
122