Data Storage and Nanomagnets Magnetic Memory: Data Storage and Nanomagnets Mark Tuominen Professor of Physics

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!

Ferromagnet uniform magnetization Bistable: Equivalent energy for 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

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.

Ferromagnet with unknown Ferromagnets are used to store data Current N S ‘0’ ? Ferromagnet with unknown magnetic state S Current N ‘1’

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

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 Perpendicular Write Head Soft Magnetic UnderLayer (SUL) coil 1 bit Y. Sonobe, et al., JMMM (2006) • CHM Goal: Make "perfect" media using self-assembled nano-templates • Also, making new designs for storage

Filling the Template: Making Cobalt Nanorods by Electrochemical Deposition WE 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

Binary Representation of Data only 2 choices one bit “1” or “0” 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 5-bit "Super Scientist" code: ex: k = 01011 1 S N OR (Coding Activity: Use attractive and repulsive forces to "read" the magnetic data!)

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

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

"Multi-state" representation of lower case letters 1 2 3 What is the word? — — — — — —