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arXiv · 1810.00446

Local-Ising type magnetic order and metamagnetism in the rare-earth pyrogermanate Er$_2$Ge$_2$O$_7$

K. M. Taddei·L. Sanjeewa·J. W. Kolis·A. S. Sefat·C. de la Cruz·D. M. Pajerowski
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Abstract

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 $RE_2$Ge$_2$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 Dy$_2$Ge$_2$O$_7$ and Ho$_2$Ge$_2$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 Er$_2$Ge$_2$O$_7$ (space group $P4_{1}2_{1}2$ ) and find the lowest yet Ne\'el 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 $P4_{1}^{'}2_{1}2^{'}$ and a refined Er moment of $m = 8.1 \mu_B$ - near the expected value for the 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 T to a lower symmetry $P2_{1}^{'}2_{1}^{'}2$ 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.

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K. M. Taddei, L. Sanjeewa, J. W. Kolis, A. S. Sefat, C. de la Cruz, D. M. Pajerowski. 2018-09-30. Local-Ising type magnetic order and metamagnetism in the rare-earth pyrogermanate Er$_2$Ge$_2$O$_7$. https://doi.org/10.1103/physrevmaterials.3.014405

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