Monopole Quasiparticle Dynamics in Spin Ice via SQUID Magnetometry

The spin ice pyrochlore class of frustrated magnets exhibits thermally-activated quasiparticle Dirac monopoles. We use SQUID magnetometry to measure magnetization fluctuations induced by the nucleation and diffusion of monopole/anti-monopole pairs in Dy2Ti2O7 single crystals and thin films grown by pulsed laser ablation. To test aspects of the monopole picture, we also probe the non-equilibrium magnetization from the imbalance of opposite-polarity monopoles induced by the simultaneous application of a temperature gradient that creates a gradient in the monopole pair density and a magnetic field that drives monopole polarities in opposite directions. Under these conditions we seek to observe the monopolar distribution, dynamics, and relaxation in and out of the spin ice regime.