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

Data Data is information iTunes

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??

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!

MAGNETISM www.ndt-ed.org/EducationResources 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"

MAGNETISM www.eia.doe.gov www.how-things-work-science-projects.com 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

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

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 “Writing” data to a ferromagnet 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.

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)

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” 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

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!)

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.)

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

Magnetic Force Microscopy Computer Hard Drive magnetic tip

Magnetic Force Microscopy Computer Hard Drive magnetic tip Topography

Magnetic Force Microscopy Computer Hard Drive magnetic tip Topography Lift height

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

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

MFM of Ring States Symmetric Rings

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.

Switching: Onion to Vortex 1 2 1 um 3 4 T. Yang, APL, 98, 242505 (2011).

Switching: Onion to Vortex 1 2 1 um 3 4 Stronger field (40 mA = 178 Oe) Weaker field (30 mA = 133 Oe) T. Yang, APL, 98, 242505 (2011).

Switching: Onion to Vortex 1 2 1 um 3 4 Stronger field (40 mA = 178 Oe) Weaker field (30 mA = 133 Oe) T. Yang, APL, 98, 242505 (2011).

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

Proof of Principle Cobalt, 12nm thick Nanotechnology, 22 (2011) 485705

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.)