The Arrhenius equation is regularly used to describe the dynamics of two-state switching in a variety of systems. The prefactor in the equation is often taken as an attempt frequency for hopping over the energy barrier. For systems larger than single particles (an electron is a single particle), the prefactor sometimes has values that are clearly not attempt frequencies. Using square permalloy dots of a size between 200 and 300 nm on a side as an idealized two-state switching system, measurements of the prefactor of the Arrhenius law changed by approximately 25 decades over a range of barrier heights from 30 meV to 2 eV. The Arrhenius prefactor ratios (detailed balance) can be fitted to a modified model that includes entropic contributions to two-state transitions. Similar considerations are likely relevant for the application of the Arrhenius law to other mesoscale systems.
Daniel Dahlberg, Professor, University of Minnesota
Host: Venkat Chandrasekhar