Probing the spin ice state in the cubic pyrochlore Ho$_{2}$Ge$_{2}$O$_{7}$

Spin ices are a remarkable magnetic ground state that can arise in geometrically frustrated pyrochlores, A$_{2}$B$_{2}$O$_{7}$, when magnetic rare earth ions are situated on the vertices of a lattice of corner sharing tetrahedra. Competing nearest-neighbor and long-range dipolar interactions result in a short-range ordered ground state for each tetrahedron in which two spins point in and two spins point out [1]. The excitations in spin ices are equally remarkable; spin ices are the only known hosts of magnetic monopoles, emergent quasiparticles with a net magnetic charge. The cubic pyrochlore Ho$_{2}$Ge$_{2}$O$_{7}$ was prepared with a high temperature and high pressure technique. Preliminary DC susceptibility, heat capacity and X-ray diffraction experiments confirmed that Ho$_{2}$Ge$_{2}$O$_{7}$ has the bulk properties of a spin ice including residual entropy equal to the Pauling value for water ice [2]. The results of a polarized neutron scattering experiment performed at ILL as well as AC susceptibility and heat capacity measurements will be presented, and compared to the canonical spin ices.\\[4pt] [1] S. T. Bramwell \textit{et al.}, Phys. Rev. Lett. \textbf{87}, 047205 (2001). \newline [2] H. Zhou \textit{et al.}, Nature Communications \textbf{2}, 478 (2011).