A New Twist on an Old Tale
Physical Review Letters: Band Filling Control of the Dzyaloshinskii-Moriya Interaction in Weakly Ferromagnetic Insulators
An international team of scientists have uncovered a surprisingly simple trend in the behaviour of 'twisted' magnets, which is precisely mirrored by first-principles calculations and explained by a simple microscopic model.
While the twisting of individual atomic-scale magnets is set to play a prominent role in future 'spintronics' technologies, the phenomenon was first discussed in detail in the context of 'weak ferromagnets' over half a century ago. It is precisely these materials that now offer a unique opportunity to investigate the effects of changing the magnetic atom type, since this causes almost no change in their structure.
Unfortunately, the direction of the magnetic twists cannot be observed by conventional techniques, since the two twist directions look the same. The researchers overcame this limitation by borrowing ideas from holography and applying them to x-ray 'diffraction', carried out at two of Europe's most powerful x-ray sources: Diamond Light Source in the UK and the European Synchrotron Radiation Source in France. The new technique gave a clear fingerprint of the twist direction, as the magnetic atoms gradually progressed along a row of the periodic table of elements. The results showed a sudden reversal of the twist, between manganese and iron, to the heavier cobalt and nickel atoms. Moreover, the jump is exactly as predicted by theory.
The team are hopeful that their results will bring new insights into an important class of material, and that their technique can be extended to other problems in solid state physics. The success of the computer simulations brings us a small step closer to goal of predicting the properties of technologically-important materials.
While the twisting of individual atomic-scale magnets is set to play a prominent role in future 'spintronics' technologies, the phenomenon was first discussed in detail in the context of 'weak ferromagnets' over half a century ago. It is precisely these materials that now offer a unique opportunity to investigate the effects of changing the magnetic atom type, since this causes almost no change in their structure.
Unfortunately, the direction of the magnetic twists cannot be observed by conventional techniques, since the two twist directions look the same. The researchers overcame this limitation by borrowing ideas from holography and applying them to x-ray 'diffraction', carried out at two of Europe's most powerful x-ray sources: Diamond Light Source in the UK and the European Synchrotron Radiation Source in France. The new technique gave a clear fingerprint of the twist direction, as the magnetic atoms gradually progressed along a row of the periodic table of elements. The results showed a sudden reversal of the twist, between manganese and iron, to the heavier cobalt and nickel atoms. Moreover, the jump is exactly as predicted by theory.
The team are hopeful that their results will bring new insights into an important class of material, and that their technique can be extended to other problems in solid state physics. The success of the computer simulations brings us a small step closer to goal of predicting the properties of technologically-important materials.
Band Filling Control of the Dzyaloshinskii-Moriya Interaction in Weakly Ferromagnetic Insulators
G. Beutier, S. P. Collins, O. V. Dimitrova, V. E. Dmitrienko, M. I. Katsnelson, Y. O. Kvashnin, A. I. Lichtenstein, V. V. Mazurenko, A. G. A. Nisbet, E. N. Ovchinnikova, and D. Pincini
Phys. Rev. Lett. 119, 167201
https://doi.org/10.1103/PhysRevLett.119.167201