Dynamics of Magnetic Charges in Spin Ice

Background: A bar magnet has two poles, denoted as +1 and -1 magnetic charges.  Patterned structures consist of many magnets (Fig. 1), where the square array (Fig. 1a) does not, whereas the honeycomb (Fig. 1b) has, net magnetic charges (or magnetic monopoles).  Under a magnetic field these local magnetic monopoles will move (Fig. 1c).  This latter structure is called “spin ice”, because it has a large number of nearly degenerate configurations.

This work: We propose a theoretical model of the dynamics in artificial spin ice under an applied magnetic field, where magnetization reversal (Fig. 2) is mediated by domain walls carrying two units of magnetic charges, in agreement with experiment.