Speaker
Description
The collective behaviour in ensembles of strongly interacting single-domain magnetic nanoparticles has been a matter of considerable interest over the past decades. Artificial Spin Ice (ASI) provides an experimental framework, where the geometry and interaction strength between mesospins, can be tailored at will. Furthermore, ASIs supporting thermal fluctuations are an ideal platform to study thermal dynamics and thermodynamic phase transitions of frustrated systems. Here, we adapt a temperature dependent A.C. susceptibility method based on the Magneto-Optical Kerr effect, a technique well known for probing relaxation dynamics in magnetic particle ensembles and spin glasses, to explore the magnetization dynamics of square ASI. A broad frequency dependent peak in the real- and imaginary-part of the A.C. susceptibility is observed, indicating a cooperative freezing of the mesospin dynamics at temperatures below the Curie temperature of the material. A comparison between ASI arrays with different lattice spacings reveals a systematic increase of the freezing temperature with stronger interactions. The thermal dynamics are well described by a Vogel-Fulcher-Tammann (VFT) law, which allows for the extraction of the energy barriers as well as the freezing temperatures of the arrays.
