Thermal and Magnetic Responses of Spin Ice via SQUID Magnetometry

The spin ice pyrochlore class of frustrated magnets exhibits quasiparticle excitations that behave like Dirac monopoles on the pyrochlore lattice. We are studying single crystals of the spin ice Dy$_2$Ti$_2$O$_7$ using dc SQUID magnetometry to look for thermal fluctuations in the monopole density. Specifically, we are seeking to observe a local excess of monopole magnetic charge induced by the simultaneous application of a temperature gradient, which should create a gradient in the monopole density, and a parallel magnetic field, which drives the flow and counterflow of oppositely-charged monopoles. This configuration should allow us to investigate the distribution, dynamics, and relaxation of the monopole-like excitations in spin ice pyrochlores.