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Local-ising-type Magnetic Order and Metamagnetism In the Rare-earth Pyrogermanate Er2ge2o7

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Physical Review Materials
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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 RE2Ge2O7,
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 Dy2Ge2O7 and Ho2Ge2O7
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 Er2Ge2O7 (space group
P41212) and nd the lowest yet Neel temperature in the pyrogermanates of 1.15 K. Using neutron
powder diffraction we nd the magnetic structure to order with k = (0, 0, 0) ordering vector, magnetic
space group symmetry P41'212' and a re fined Er moment of m = 8.1uB - near the expected
value for the Er3+ 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 ~ 0.35 T to
a lower symmetry P21'21'2 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.