Magnetic Memory Data Storage and Nanomagnets Mark Tuominen

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

Review Data Storage. Example: Advancement of the i. Pod 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 “topview” shorthand H Mz hysteresis curve H E = K 1 sin 2 ��� • 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 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/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 Y. Sonobe, et al. , JMMM (2006) Soft Magnetic Under. Layer (SUL) • 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 Co 2+ 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 2 n 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 0 1 1 S N OR S N N N S S 0 (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? ——————