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X-ray holograms expose secret magnetism

Publication date: May 2, 2007 4:54:40 PM

Collaborative research between scientists in the UK and USA has led to a major breakthrough in the understanding of antiferromagnets, published in this week’s Nature. Scientists at the London Centre for Nanotechnology, the University of Chicago and the Center for Nanoscale Materials at Argonne National Laboratory have used x-rays to see the internal workings of antiferromagnets for the very first time.

Unlike conventional magnets, antiferromagnets (such as the metal chromium) are materials which exhibit ‘secret’ magnetism, undetectable at a macroscopic level. Instead, their magnetism is confined to very small regions where atoms behave as tiny magnets. They spontaneously align themselves opposite to adjacent atoms, leaving the material magnetically neutral overall.

Professor Gabriel Aeppli, Director of the London Centre for Nanotechnology, said: “People have been familiar with ferromagnets for hundreds of years and they have countless everyday uses; everything from driving electrical motors to storing information on hard disk drives. We haven’t been able to make the same strides with antiferromagnets because we weren’t able to look inside them and see how they were ordered.

“This breakthrough takes our understanding of the internal dynamics of antiferromagnets to where we were ninety years ago with ferromagnets. Once you can see something, it makes it that much easier to start engineering it.”

The magnetic characteristics of ferromagnets have been studied by scientists since Greek antiquity, enabling them to build up a detailed picture of the regions - or “magnetic domains” - into which they are divided. However, antiferromagnets remained a mystery because their internal structure was too fine to be measured.

The internal order of antiferromagnets is on the same scale as the wavelength of x-rays (below 10 nanometers). The latest research used x-ray photon correlation spectroscopy to produce ‘speckle’ patterns; holograms which provide a unique ‘fingerprint’ of a particular magnetic domain configuration.

Dr. Eric D. Isaacs, Director of the Center for Nanoscale Materials, said: “Since the discovery of x-rays over 100 years ago, it has been the dream of scientists and engineers to use them to make holographic images of moving objects, such as magnetic domains, at the nanoscale.

“This has only become possible in the last few years with the availability of sources of coherent x-rays, such as the Advanced Photon Source, and the future looks even brighter with the development of fully coherent x-ray sources called Free Electron Lasers over the next few years.”

In addition to producing the first antiferromagnet holograms, the research also showed that their magnetic domains shift over time, even at the lowest of temperatures. The most likely explanation for this can be found in quantum mechanics and the experiments open the door to the future exploitation of antiferromagnets in emerging technologies such as quantum computing.

“The key finding of our research provides information on the stability of domain walls in antiferromagnets,” said Oleg Shpyrko, lead author on the publication and researcher at the Center for Nanoscale Materials. “Understanding this is the first step towards engineering antiferromagnets into useful nanoscale devices that exploit it.”

Work at the London Centre for Nanotechnology was funded by a Royal Society Wolfson Research Merit Award and the Basic Technology program of Research Councils UK. Work at the Center for Nanoscale Materials and the Advanced Photon Source was supported by the DOE Office of Science, Office of Basic Energy Sciences. The work at the University of Chicago was supported by the National Science Foundation.

Notes to editors:

Contact details:

For more information, please contact Dave Weston at the London Centre for Nanotechnology on tel: +44 (0)20 7679 7678, mobile: +44 (0) 7733 307 596, out of hours +44 (0)7917 271 364, e-mail: d.weston@ucl.ac.uk

Images:

A full colour image of a coherent x-ray speckle pattern can be obtained by calling the London Centre for Nanotechnology on +44 (0)20 7679 7678 or by emailing d.weston@ucl.ac.uk.

About the London Centre for Nanotechnology

The London Centre for Nanotechnology is a joint enterprise between University College London and Imperial College London. In bringing together world-class infrastructure and leading nanotechnology research activities, the Centre aims to attain the critical mass to compete with the best facilities abroad. Furthermore by acting as a bridge between the biomedical, physical, chemical and engineering sciences the Centre will cross the 'chip-to-cell interface' - an essential step if the UK is to remain internationally competitive in biotechnology. Website: www.london-nano.ucl.ac.uk

About UCL

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. In the government’s most recent Research Assessment Exercise, 59 UCL departments achieved top ratings of 5* and 5, indicating research quality of international excellence.

UCL is the fourth-ranked UK university in the 2006 league table of the top 500 world universities produced by the Shanghai Jiao Tong University. UCL alumni include Mahatma Gandhi (Laws 1889, Indian political and spiritual leader); Jonathan Dimbleby (Philosophy 1969, writer and television presenter); Junichiro Koizumi (Economics 1969, Prime Minister of Japan); Lord Woolf (Laws 1954, Lord Chief Justice of England & Wales); Alexander Graham Bell (Phonetics 1860s, inventor of the telephone), and members of the band Coldplay.

About Imperial College London

Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (11,000) and staff (6,000) of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that enhance the quality of life and the environment - underpinned by a dynamic enterprise culture. Website: www.imperial.ac.uk

About Argonne National Laboratory

The USA’s first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Since 1990, Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

About the Center for Nanoscale Materials

The Center for Nanoscale Materials, or CNM, at Argonne is a joint partnership between the U.S. Department of Energy and the State of Illinois, as part of DOE’s Nanoscale Science Research Center program. The CNM serves as a user-based facility, providing the expertise and capabilities for nanoscience and nanotechnology research. The CNM’s mission includes supporting basic research and the development of advanced instrumentation that will help generate new scientific insights and create new materials with entirely new properties. The existence of the CNM, with its centralized facilities, controlled environments, technical support and scientific staff enables researchers to excel and significantly extend their reach.

About the University of Chicago

Founded by oil magnate John D. Rockefeller, the University of Chicago is a private, nondenominational institution of higher learning. Scientists at the University are working at the cutting edge of virtually every field of science, from cosmological astrophysics to molecular genetics and from high-energy particle physics to psychoneuroimmunology. Seventy-nine recipients of the Nobel Prize have been researchers, students or faculty members at the University at some point in their careers. Web site: www.uchicago.edu.

About Research Councils UK

The seven Research Councils are independent non-departmental public bodies, funded by the Science Budget through the Office of Science and Innovation. They are incorporated by Royal Charter and together manage a research budget of over £2.8 billion a year.

Research Councils UK (RCUK) is the partnership between the UK's seven Research Councils. Through RCUK, the Research Councils work together to champion the research, training and innovation they support.

The seven UK Research Councils are:

Arts & Humanities Research Council (AHRC) Biotechnology & Biological Sciences Research Council (BBSRC) Economic & Social Research Council (ESRC) Engineering & Physical Sciences Research Council (EPSRC) Medical Research Council (MRC) Natural Environment Research Council (NERC) Science and Technology Facilities Council (STFC)