Debye-Hückel theory for spin ice at low temperature

Abstract

At low temperatures, spin ice is populated by a finite density of magnetic monopoles-pointlike topological defects with a mutual magnetic Coulomb interaction. We discuss the properties of the resulting magnetic Coulomb liquid in the framework of Debye H\"{u}ckel theory, for which we provide a detailed context-specific account. We discuss both thermodynamical and dynamical signatures, and compare Debye H\"{u}ckel theory to experiment as well as numerics, including data for specific heat and AC susceptibility. We also evaluate the entropic Coulomb interaction which is present in addition to the magnetic one and show that it is quantitatively unimportant in the current compounds. Finally, we address the role of bound monopole anti-monopole pairs and derive an expression for the monopole mobility.