PIER Photon Science Colloquium: Artificial spin ice: Frustration, emergent magnetic monopoles and thermal behaviour

by Laura Heyderman (Paul Scherrer Institute, Villingen; ETH, Zurich, Switzerland)

Friday, June 7, 2013 from to (Europe/Berlin)
at DESY Hamburg ( CFEL Lecture Hall, Bldg. 99 )
Artificial spin ice, consisting of 2D arrays of dipolar coupled nanomagnets with specific arrangements, allows the study of frustration by tailoring the array geometry and observation of the magnetic configurations with various microscopy techniques.

We focus on artificial kagome spin ice with elongated monodomain nanomagnets forming an array of hexagonal rings and employ synchrotron x-ray photoemission electron microscopy (PEEM) to characterize the magnetic states. Starting with the basic structures with one, two and three hexagonal rings, we found that demagnetization did not lead to the ground state for larger structures. Observation of magnetization reversal in infinite artificial kagome spin ice has allowed real space observations of emergent magnetic monopoles with their associated Dirac strings.

Recently we have realized a method to create artificial spin ice with fluctuating moments and observed the evolving magnetic configurations with PEEM, which can be understood by considering the dipolar energy landscape. These thermally active systems open the door to microscopic studies of relaxation processes and provide a controlled route to the lowest-energy state.