Research: The importance of the weak

2018-02-13

Researchers at the Division of Material Physics at Uppsala University have shown how the collective dynamics in a structure consisting of interacting magnetic nano-islands can be altered to possess liquid-like qualities, as well as promoting emergent magnetic states. Their findings are published in the scientific journal Nature Physics.

Illustration of the sample where the white arrows depict the magnetization direction within each magnetic island. Image: Erik Östman.

With the aid of state-of-the-art nano-fabrication the researchers have created a 2D array of small magnetic islands. The interaction between the elements is finely tuned by interaction modifiers, which dramatically changes the properties of the system.

“It is fascinating that with the addition of these interaction modifiers, the magnetic state of the array can be tuned from a well ordered state towards a liquid-like state, where local order is coexisting with long range disorder.” says Erik Östman, PhD student in Materials Physics at Uppsala University.

The small magnetic islands, or artificial atoms, exhibit thermal fluctuations, allowing for time and temperature dependent observations of the evolution of the liquid-like state. This has previously been unachievable, since systems exhibiting similar phenomena, do so on an atomic level at extremely low temperatures.

The researcher have, in addition to the liquid-like state, identified another magnetic state where groups of artificial atoms create a unit with specific properties, dictating the overall magnetic order. This is an example of emergent behavior.

The magnetic states were observed with microscopy methods and subsequently analyzed with mathematical tools usually associated with scattering experiments. This opens up for the possibility of performing scattering experiments on similar systems, in order to further improve the understanding of the order and dynamics in such structures.

“This is basic science, but the results from this research will have a strong impact on parallel ongoing activities in our division, where we explore the potential of utilizing such structures for the active control of light and fabrication of reconfigurable flat optics” says Vassilios Kapaklis, Associate Professor in Materials Physics at Uppsala University.

“The connection to e.g. electromagnetic radiation can be used both to probe emergent phenomena as well as being able to perform calculations in a completely new way. The construction of both ESS and MAXIV in Sweden will be very useful to explore this new fascinating world” says Björgvin Hjörvarsson, professor in materials physics at Uppsala University.

The work was done in collaboration with the Center for Functional Nanomaterials, Brookhaven National Laboratory in the USA, and the Advanced Light Source in Berkeley, USA.

The research was financed by the Swedish Research Council (VR), Knut and Alice Wallenberg Foundation, the Göran Gustafsson Foundation, the Swedish Foundation for International Cooperation in Research and Higher Education (STINT), and European Research Council.

Article

Interaction modifiers in artificial spin ices, Erik Östman, Henry Stopfel, Ioan-Augustin Chioar, Unnar B. Arnalds, Aaron Stein, Vassilios Kapaklis & Björgvin Hjörvarsson, Nature Physics, doi:10.1038/s41567-017-0027-2