XY Antiferromagnetic Ground State in the Effective S=1/2 Pyrochlore Yb2Ge2O7

TL;DR

This study investigates the magnetic ground state of Yb2Ge2O7, revealing an XY antiferromagnetic order with a transition at 0.57 K, using neutron scattering and muSR techniques to characterize its quantum magnetic properties.

Contribution

The paper provides detailed experimental characterization of Yb2Ge2O7's magnetic ground state, including crystal electric field levels and magnetic ordering, highlighting its XY antiferromagnetic nature.

Findings

Yb2Ge2O7 has an S_eff=1/2 ground state with XY anisotropy.

Magnetic ordering occurs at T_N=0.57 K with a small ordered moment.

The ground state exhibits a transition to a Gamma_5 magnetic structure.

Abstract

We report neutron scattering and muon spin relaxation measurements (muSR) on the pyrochlore antiferromagnet Yb2Ge2O7. Inelastic neutron scattering was used to probe the transitions between crystal electric field levels, allowing us to determine the eigenvalues and eigenvectors appropriate to the J=7/2 Yb3+ ion in this environment. The crystal electric field ground state doublet in Yb2Ge2O7 corresponds primarily to m_J = +/- 1/2 with local XY anisotropy, consistent with an S_eff = 1/2 description for the Yb moments. muSR measurements reveal the presence of an ordering transition at T_N = 0.57 K with persistent weak dynamics in the ordered state. Finally, we present neutron diffraction measurements that reveal a clear phase transition to the k = (000) Gamma_5 ground state with an ordered magnetic moment of 0.3(1) mu_B per Yb ion. We compare and contrast this phenomenology with the low temperature behavior of Yb2Ti2O7 and Er2Ti2O7, the prototypical S_eff = 1/2 XY pyrochlore magnets.