1. Data Storage and Nanomagnets
Magnetic Memory:
Data Storage and Nanomagnets
Mark Tuominen
UMass
Kathy Aidala
Mount Holyoke College

2. Data
Data is information
iTunes

3. How do we store data digitally?
Everything is reduced to binary, a “1” or a “0”.
We look for ways to represent 1 or 0, which means we need to find physical systems with two distinct states.
We have to be able to switch the state of the system if we want to “write” data.
The bit has to stay that way for long enough.
We have to be able to “read” if the bit is a zero or one to use the data.
What physical systems have these properties??

4. Data Storage. Example: Advancement of the iPod
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!

5. MAGNETISM I B
It is always useful to start the introduction with something simple such that anyone could get something out of the talk. This page introduces the concept of a single-domain nanomagnet as a basic element for data storage. Note that the animation helps to tell the story in a linear and logical way. Please add actual diagrams of the double well for the three fields shown.
Electrical current produces a magnetic field: "electromagnetism"

6. MAGNETISM
It is always useful to start the introduction with something simple such that anyone could get something out of the talk. This page introduces the concept of a single-domain nanomagnet as a basic element for data storage. Note that the animation helps to tell the story in a linear and logical way. Please add actual diagrams of the double well for the three fields shown.
myfridge
Refrigerator magnets provide an external magnetic field, permanently; no wires, no power supply and no current needed.
Permanent Magnets = FERROMAGNETS

7. Ferromagnet uniform magnetization
Electron magnetic moments ("spins")
Aligned by
"exchange interaction"
anisotropy axis
("easy" axis)
It is always useful to start the introduction with something simple such that anyone could get something out of the talk. This page introduces the concept of a single-domain nanomagnet as a basic element for data storage. Note that the animation helps to tell the story in a linear and logical way. Please add actual diagrams of the double well for the three fields shown.
Bistable ! Equivalent energy for "up" or "down” states
Iron, nickel, cobalt and many alloys are ferromagnets

8. The Bistable Magnetization of a Nanomagnet
• A single-domain nanomagnet with a single “easy axis” (uniaxial anisotropy) has two stable magnetization states Mz Mz z or H Mz H
hysteresis curve
“topview”
shorthand
switching field
E = K1sin2•H
It is always useful to start the introduction with something simple such that anyone could get something out of the talk. This page introduces the concept of a single-domain nanomagnet as a basic element for data storage. Note that the animation helps to tell the story in a linear and logical way. Please add actual diagrams of the double well for the three fields shown.
Bistable! Ideal for storing data - in principle, even one nanomagnet per bit.

9. Ferromagnet with unknown
“Writing” data to a ferromagnet
Current N S
‘0’ ?
Ferromagnet with unknown
magnetic state S
Current N
‘1’

10. Magnetic Data Storage
A computer hard drive stores your data magnetically
“Read”
Head
Signal
“Write”
Head
current S N
Disk N S 1 _
“Bits” of
information
direction of disk motion

11. 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.

12. Nanofabrication with self-assembled
“cylindrical phase” diblock copolymer films
Deposition
Template
Remove polymer
block within cylinders
(expose and develop)
UMass/IBM: Science 290, 2126 (2000)

13. Filling the Template: Making Cobalt Nanorods by Electrochemical DepositionWE
REF
electrolyte CE
For the published part of our results, we chose another approach to electrodeposite the Co magnetic cluster for our experiments. This procedure had been studied thougrhtouly by my colleague Dr. Ursache in our lab. The deposition electrolyte is carefully tuned to pH6, And we used PRECD. the voltage we applied to the working electrode in the potentialstat ECD cell can be timed to two phases. Each of the repeating phases is 10 ms long. In the pulse phase, the voltage we put on the working electrode is 1 V to the standard reference electrode. The Co atoms are deposited into the pattern. But not all of the Co atoms can land on the perfect crystal lattice points. During the reverse cycle, the voltage we put on the working electrode is 0.35 V. This will remove the loosely bonded Co atoms back into the solution.
metal

14. Binary Representation of Data
only 2 choices
one bit
“1” or “0” or
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

15. Binary representation of lower case letters
5-bit "Super Scientist" code:
For example, k = 01011 1 S N OR
(Coding Activity: Use attractive and repulsive forces to "read" the magnetic data!)

16. Ferromagnetic Nanorings as Memory
"0"
"1"
Vortex Magnetization
Nanotechnology(2008); PRB (2009)
Pt solid tip
Researchers from the NSF Center for Hierarchical Manufacturing at UMass developed a new method for making metal rings at unprecedented small sizes. These small rings are being developed for applications in magnetic data storage and photonics. (Image credits by graduate students Lizzy Yang, Qijun Xiao and Deepak Singh of the Tuominen group in the Physics Department.)

17. AFM: Electromagnetic Forces
Anything that creates a force on the tip can be “imaged”
Electromagnetic force is long range, but generally weaker than the repulsive forces at the surface
Image electromagnetic forces 10 – 100nm above the surface
Lift height

18. Magnetic Force Microscopy
Computer Hard Drive
magnetic tip

19. Magnetic Force Microscopy
Computer Hard Drive
magnetic tip
Topography

20. Magnetic Force Microscopy
Computer Hard Drive
magnetic tip
Topography
Lift height

21. Magnetic Force Microscopy
Computer Hard Drive
magnetic tip
Topography
Lift height
Magnetism

22. Magnetic Force Microscopy
Image contrast is proportional to the derivative of the magnetic field
Magnetic
state
dB/dz small
dB/dz large, negative
dB/dz large, positive
200 nm
Bar magnet- approx 1 micron tall and 250nm wide (ish) 20nm thick
MFM
simulation

23. MFM of Ring States
Symmetric Rings

24. MFM of Ring States Symmetric Rings vortex onion
No contrast in the vortex state in a perfect ring. Cannot determine circulation (CW or CCW)
Light and Dark spots indicate Tail to Tail and Head to Head domain walls.

25. Switching: Onion to Vortex1 2
1 um 3 4
T. Yang, APL, 98, (2011).

26. Switching: Onion to Vortex1 2
1 um 3 4
Stronger field
(40 mA = 178 Oe)
Weaker field
(30 mA = 133 Oe)
T. Yang, APL, 98, (2011).

27. Switching: Onion to Vortex1 2
1 um 3 4
Stronger field
(40 mA = 178 Oe)
Weaker field
(30 mA = 133 Oe)
T. Yang, APL, 98, (2011).

28. Improved MRAM Proposal
Zhu 2008 Proceedings of the IEEE Vol. 96, No. 11, November
Trapped DWs lead to lower switching current
Zhu, Proceedings of the IEEE 96(11), 1786 (2008)

29. Proof of Principle
Cobalt, 12nm thick
Nanotechnology, 22 (2011)

31. Ferromagnetic Nanorings as Memory
"0"
"1"
Vortex Magnetization
Pt solid tip
Nanotechnology(2008); PRB (2009)
Aidala and Tuominen, APL (2011); Nanotech. 2011; J.A.P. 2012
Manipulation of magnetization with local circular field
Researchers from the NSF Center for Hierarchical Manufacturing at UMass developed a new method for making metal rings at unprecedented small sizes. These small rings are being developed for applications in magnetic data storage and photonics. (Image credits by graduate students Lizzy Yang, Qijun Xiao and Deepak Singh of the Tuominen group in the Physics Department.)