Magnetic Monopole Current in Artificial Square Spin Ice

Sammanfattning: Recent theoretical and experimental results have revealed the existence of magnetic monopoles, in the form of quasi particles, in both condensed matter known as spin ice, as well as in two-dimensional artificial versions of the same material. In this report a two-dimensional Ising model is first examined, then an artificial square spin ice model using a dipole approximation, only taking into account nearest and next nearest neighbors. The Metropolis algorithm is used to obtain the internal energy, specific heat capacity and entropy as functions of temperature. In the latter model the magnetic monopole concentration and monopole current is also simulated. The two models show similar quantitative behavior in the above mentioned physical quantities, and in comparison to previously published results. In the artificial square spin ice model, under the influence of a magnetic field, a rapidly decreasing monopole current is observed, which decreases faster for higher temperatures. The magnitude of the magnetic field plays a significant role in the generation of the monopole current, and no direct effect of the phase transitionis observed.