Quenched crystal field disorder and magnetic liquid ground states in Tb2Sn2-xTixO7

TL;DR

This study investigates how B-site disorder in Tb2Sn2-xTixO7 affects its magnetic ground state, revealing a novel, highly disordered magnetic phase with continuum-like crystal field levels and extreme random anisotropy.

Contribution

It demonstrates that B-site disorder induces a unique magnetic ground state with continuum crystal field levels, advancing understanding of disorder effects in quantum spin ice materials.

Findings

Low susceptibility and strong spin fluctuations below 0.1 K.

Neutron spectroscopy shows continuum crystal field levels at high B-site mixing.

Ground state resembles an extreme random-anisotropy magnet.

Abstract

Solid-solutions of the "soft" quantum spin ice pyrochlore magnets Tb2B2O7 with B=Ti and Sn display a novel magnetic ground state in the presence of strong B-site disorder, characterized by a low susceptibility and strong spin fluctuations to temperatures below 0.1 K. These materials have been studied using ac-susceptibility and muSR techniques to very low temperatures, and time-of-flight inelastic neutron scattering techniques to 1.5 K. Remarkably, neutron spectroscopy of the Tb3+ crystal field levels appropriate to at high B-site mixing (0.5 < x < 1.5 in Tb2Sn2-xTixO7) reveal that the doublet ground and first excited states present as continua in energy, while transitions to singlet excited states at higher energies simply interpolate between those of the end members of the solid solution. The resulting ground state suggests an extreme version of a random-anisotropy magnet, with many local moments and anisotropies, depending on the precise local configuration of the six B sites neighboring each magnetic Tb3+ ion.