Speaker
Description
Avalanches are phenomena in which there is a cascade-like transition between two states and are present in many material systems, e.g. flux penetration into superconductors. Generally, avalanches are pinned at defects however, these defects are difficult to control and thus the study of the avalanche process is rather difficult. In this work, we utilize the customization properties of artificial spin ice (ASI) to tune island size, array geometry, and interaction distance such that we can directly control avalanche processes.
Nanostructured films are fabricated using e-beam lithography with island size of 220 nm x 80 nm. The islands were deposited via molecular beam deposition and are composed of 15 nm of Ni81Fe19 with a 2 nm Al cap on Si3N4 coated Si substrates with various array sizes (L = 40-100 islands). Magnetic imaging was performed with magnetic force microscopy at remnance after the islands were exposed to a variety of magnetic fields from zero to fully polarized. We find that we can induce avalanches of various sizes in the ASI structures and that the probability (P) of having an avalanche of size s follows exponential decay behavior until the array size is reduced to 40 islands when finite size effects dominate. These results are used to study the avalanche processes and effects of finite system size, as well as the relevant scaling of the avalanche process. This work is funded by the US Department of Energy (DE-SC0010778). Work at the University of Minnesota is supported by NSF.
