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Nanomagnetic Imaging


The microscopic arrangement of the magnetic structure within a thin metal film plays a fundamental role in many technological applications ranging from information storage in computer hard drives to anti-lock brake sensors in automobiles. NIST researchers have developed a technique, called scanning electron microscopy with polarization analysis (SEMPA), that can reveal the magnetic structure of such materials with nanoscale resolution and without disturbing the magnetization. The technology is useful for understanding and developing a wide range of electronics systems that rely on magnetic properties instead of electric charge to process and store information.


Scanning electron microscopy is widely used to examine the surfaces of materials used in computers and other electronic devices. Detecting how a beam of electrons scatters off the surface gives a topographical picture of its peaks and valleys. In addition, the electrons released from the surface by the incoming beam carry information about the material's electronic structure. And for a ferromagnetic material such as iron, scanning electron microscopy can map out surface magnetic structure.

A ferromagnetic material, such as iron, becomes permanently magnetized when its electrons all align in the same direction. Electrons behave like little magnets, with alignment corresponding to the orientation of their spins. When a beam of electrons interacts with a magnetic surface, the spins of the electrons emitted from the surface reflect the surface's magnetic orientation.

Project researchers have developed a method to detect the spins of these ejected electrons from which they can create a magnetic map of the surface with different colors corresponding to different magnetic directions. In other magnetic imaging techniques, such as magnetic force microscopy, a tiny magnetic probe interacts with the surface, potentially altering its magnetization. The technique, called scanning electron microscopy with polarization analysis (SEMPA), does not disrupt the magnetic properties of the surface being measured.

Ferromagnetic surfaces and thin films with increasingly small-scale structures are important for building smaller circuits and storing data at higher densities. SEMPA can examine films just a few atoms thick at a resolution of ten nanometers. As a diagnostic tool, it allows industry researchers to get detailed magnetic maps of surfaces, a capability that aids in device design and improvement.

More generally, use of SEMPA to better understand magnetic properties at the nanoscale has a wide range of applications. One example being actively investigated by NIST researchers is magnetic random access memory (MRAM) for computers, which uses electronic spin to store and read data. SEMPA is also helping researchers measure the magnetic properties of oxides and other emerging magnetic materials, and to probe how magnetic interactions within materials differ on the nanoscale compared to the macroscale.

SEMPA is contributing to a growing field called spintronics, which uses electron spins rather than charge to encode the 1s and 0s of binary data. With SEMPA, NIST researchers have provided a versatile tool that can refine today’s technology and will help develop future devices that make use of magnetic properties.

Selected Publications:
  • Simultaneous imaging of the ferromagnetic and ferroelectric structure in multiferroic heterostructures, J. Unguris, S. R. Bowden, D. T. Pierce, M. Trassin, R. Ramesh, S.-W. Cheong, S. Fackler, and I. Takeuchi, APL Materials 2, 076109 (2014).
    NIST Publication Database        Journal Web Site
  • Optimization of spin-triplet supercurrent in ferromagnetic Josephson junctions, C. Klose, T. S. Khaire, Y. Wang, W. P. Pratt, N. O. Birge, B. J. McMorran, T. P. Ginley, J. A. Borchers, B. J. Kirby, B. B. Maranville, and J. Unguris, Physical Review Letters 108, 127002 (2012).
    NIST Publication Database        Journal Web Site
  • Electron vortex beams with high quanta of orbital angular momentum, B. J. McMorran, A. Agrawal, I. M. Anderson, A. A. Herzing, H. J. Lezec, J. J. McClelland, and J. Unguris, Science 331, 192 -195 (2011).
    NIST Publication Database
            Journal Web Site
  • Direct imaging of current-driven domain walls in ferromagnetic nanostripes, W. C. Uhlig, M. J. Donahue, D. T. Pierce, and J. Unguris, Journal of Applied Physics 105, (2009).
    NIST Publication Database
            Journal Web Site
  • SEMPA imaging for spintronics applications, J. Unguris, S. H. Chung, and D. T. Pierce, in Characterization and Metrology for Nanoelectronics: 2007 International Conference on Frontiers of Characterization and Metrology (2007), p. 472-476.
    NIST Publication Database
            Journal Web Site



Lead Organizational Unit:



NVE Corporation
Joe Davies
Kevin Johnson
Charles Kuo
David Abraham
Stuart Parkin
University of California, Berkeley
Morgan Trassin
Ramamoorthy Ramesh
Yuri Suzuki
University of California, Davis
Kai Liu
Dustin Gilbert
Randy Dumas
University of California, Los Angeles
Greg Carman
Wei-Yang Sun
University of Kentucky
Lance Delong
Barry Farmer
Northeastern University
Nian Sun
Ziyao Zhou
Johns Hopkins University
Chia-Ling Chien
University of Maryland, College Park
Ichiro Takeuchi
Alison Flatau
Tsinghua University
Yonggang Zhao
University of Paris - Sud
Jacques Miltat
Massachusetts Institute of Technology
Caroline Ross
Michigan State University
William Pratt
Norman Birge
Amit Agrawal
Ian Anderson
Andrew Herzing
Henri Lezec

Facilities/Tools Used:


Andy Balk - NIST/UMD
Ian Gilbert - NIST/UMD
Daniel T. Pierce - NIST
John Unguris - NIST
Robert McMichael - NIST
Mark Stiles - NIST

John Unguris, Phone 301-975-3712

100 Bureau Dr., MS 6202
Gaithersburg, MD 20899-6202