The recent discoveries of proximate quantum spin-liquid compounds and their potential application in quantum computing informs the search for new candidate materials for quantum spin-ice and spin-liquid physics. While the majority of such work has centered on members of the pyrochlore family due to their inherently frustrated linked tetrahedral structure, the rare-earth pyrogermanates also show promise for possible frustrated magnetic behavior. With the familiar stoichiometry $R_2{\mathrm{Ge}}_2{\mathrm{O}}_7$, these compounds generally have tetragonal symmetry with a rare-earth sublattice built of a spiral of alternating edge and corner-sharing rare-earth site triangles. Studies on ${\mathrm{Dy}}_2{\mathrm{Ge}}_2{\mathrm{O}}_7$ and ${\mathrm{Ho}}_2{\mathrm{Ge}}_2{\mathrm{O}}_7$ have shown tunable low temperature antiferromagnetic order, a high frustration index, and spin-ice-like dynamics. Here we use neutron diffraction to study magnetic order in ${\mathrm{Er}}_2{\mathrm{Ge}}_2{\mathrm{O}}_7$ (space group $P{4}_1{2}_{1}2$) and find the lowest yet Neél temperature in the pyrogermanates of 1.15 K. Using neutron powder diffraction, we find the magnetic structure to order with $k=(0,0,0)$ ordering vector, magnetic space group symmetry $P{4}_1^{{}^{\prime }}{2}_1{2}^{{}^{\prime }}$, and a refined Er moment of $m=8.1{\mu }_B$ near the expected value for the ${\mathrm{Er}}^{3+}$ free ion. Provocatively, the magnetic structure exhibits similar “local Ising” behavior to that seen in the pyrocholres where the Er moment points up or down along the short Er-Er bond. Upon applying a magnetic field, we find a first-order metamagnetic transition at $\sim 0.35\mathrm{T}$ to a lower symmetry $P{2}_1^{{}^{\prime }}{2}_1^{{}^{\prime }}2$ structure. This magnetic transition involves an inversion of Er moments aligned antiparallel to the applied field describing a class I spin-flip-type transition, indicating a strong local anisotropy at the Er site—reminiscent of that seen in the spin-ice pyrochlores.

• Received 30 September 2018
• Revised 30 November 2018

DOI:https://doi.org/10.1103/PhysRevMaterials.3.014405