X-ray Holograms reveal Secret Magnetism

Antiferromagnetism is a different manifestation of magnetism, where the spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. The antiferromagnetic materials are relatively uncommon and their properties are still not fully understood.

Unlike ferromagnets, which have been studied since Greek antiquity, antiferromagnets remained a mystery because their internal structure was too fine to be measured.

A joint research between scientists in the USA and the UK has produced a major breakthrough in the understanding of the processes linked to the unusual behavior of these materials. Antiferromagnets, like chromium, seem to have a secret magnetism, macroscopically undetectable. In tiny regions, their atoms behave like nanoscopic magnets, by spontaneously aligning themselves opposite to adjacent atoms, leaving the material magnetically neutral overall.

The experiment took advantage of the fact that their internal structure is on the same scale as the wavelength of x-rays (below 10 nanometers). So, the scientists used x-ray photon correlation spectroscopy to produce "speckle" patterns, which are holograms providing a unique "fingerprint" of a particular magnetic domain configuration.

The lead researcher, 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."

Producing the first antiferromagnet holograms is a huge step forward in the understanding of the strange materials, now that there's proof that their magnetic domains shift over time, even at the lowest of temperatures.

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."

Practical applications of the new findings could be used in emerging technological fields, like quantum computers.