Ground state selection in XY pyrochlore antiferromagnets R$_{2}$Ge$_{2}$O$_{7}$ (R = Er, Yb)

TL;DR

This study investigates the magnetic ground states of Er$_{2}$Ge$_{2}$O$_{7}$ and Yb$_{2}$Ge$_{2}$O$_{7}$ pyrochlores, revealing specific antiferromagnetic orderings and unifying their behaviors through XY exchange interactions influenced by chemical pressure.

Contribution

It demonstrates the ground state selection in these pyrochlores and unifies various R$_{2}$B$_{2}$O$_{7}$ compounds' magnetic phases via an enlarged XY exchange interaction model.

Findings

Er$_{2}$Ge$_{2}$O$_{7}$ has a $ ext{ψ}_3$ ground state.

Yb$_{2}$Ge$_{2}$O$_{7}$ exhibits $ ext{ψ}_2$ or $ ext{ψ}_3$ phases.

Magnetic ground states are unified through the XY exchange interaction $J_{ ext{±}}$.

Abstract

Elastic neutron scattering, ac susceptibility, and specific heat experiments on the pyrochlores Er$_{2}$Ge$_{2}$O$_{7}$ and Yb$_{2}$Ge$_{2}$O$_{7}$ show that both systems are antiferromagnetically ordered in the $\Gamma_5$ manifold. The ground state is a $\psi_{3}$ phase for the Er sample and a $\psi_{2}$ or $\psi_{3}$ phase for the Yb sample, which suggests "Order by Disorder"(ObD) physics. Furthermore, we unify the various magnetic ground states of all known R$_{2}$B$_{2}$O$_{7}$ (R = Er, Yb, B = Sn, Ti, Ge) compounds through the enlarged XY type exchange interaction $J_{\pm}$ under chemical pressure. The mechanism for this evolution is discussed in terms of the phase diagram proposed in the theoretical study [Wong et al., Phys. Rev. B 88, 144402, (2013)].