‘Local-Ising’ type magnetism and metamagnetism in the rare-earth pyrogermanates

The rare-earth pyrochlores have long been the system of choice for the study of frustrated magnetism due to the inherent geometric frustration of the rare-earth sublattice which can beget ‘local-Ising’ behavior. The combination of a large local-anisotropy and geometric frustration lead to the famous ‘spin-ice’ rules and consequently to exotic physics such as magnetic monopoles. The rare-earth pyrogermanate family of materials has seen significantly less study yet has similar potential due to a spiraling triangular rare-earth sublattice. We report the results of neutron scattering experiments on rare-earth pyrogermanate Er₂Ge₂O₇ which reveal a 3D spiral magnetic structure below 1.2 K. Under applied field we find a metamagnetic transition of spin-flip type indicating a large local anisotropy of the rare-earth site. This transition selectively inverts magnetic moments anti-parallel to the applied field yet leaves to moments along their locally determined easy-axis. This describes a local-Ising type behavior as seen in the spin-ice pyrochlores and encourages further study of these materials.