Antiferromagnetic order in the pyrochlores R2Ge2O7 (R=Er,Yb)

Elastic neutron scattering, ac susceptibility, and specific heat experiments on the pyrochlores Er2Ge2O7 and Yb2Ge2O7 show that both systems are antiferromagnetically ordered in the Γ5 manifold. The ground state is a ψ3 phase for the Er sample and a ψ2 or ψ3 phase for the Yb sample, which suggests “Order by Disorder” physics. Furthermore, we unify the various magnetic ground states of all known R2X2O7 (R=Er, Yb; X=Sn, Ti, Ge) compounds through the enlarged XY-type exchange interaction J± under chemical pressure. The mechanism for this evolution is discussed in terms of the phase diagram proposed in the theoretical study by Wong et al. [Phys. Rev. B 88, 144402 (2013)PRBMDO1098-012110.1103/PhysRevB.88.144402].