Coulomb spin liquid in anion-disordered pyrochlore Tb$_2$Hf$_2$O$_7$

TL;DR

This study reveals that controlled anion disorder in Tb$_2$Hf$_2$O$_7$ pyrochlore suppresses magnetic order and stabilizes a Coulomb spin liquid state characterized by strong fluctuations and defect-induced frozen moments.

Contribution

It demonstrates how anion Frenkel disorder influences magnetic ground states, leading to a tunable spin liquid phase in a pyrochlore system.

Findings

Disorder prevents long-range magnetic order at low temperatures.

A Coulomb spin liquid state with strong fluctuations is stabilized.

Disorder induces defect-related frozen magnetic moments.

Abstract

The charge ordered structure of ions and vacancies characterizing rare-earth pyrochlore oxides serves as a model for the study of geometrically frustrated magnetism. The organization of magnetic ions into networks of corner-sharing tetrahedra gives rise to highly correlated magnetic phases with strong fluctuations, including spin liquids and spin ices. It is an open question how these ground states governed by local rules are affected by disorder. In the pyrochlore Tb$_2$Hf$_2$O$_7$, we demonstrate that the vicinity of the disordering transition towards a defective fluorite structure translates into a tunable density of anion Frenkel disorder while cations remain ordered. Quenched random crystal fields and disordered exchange interactions can therefore be introduced into otherwise perfect pyrochlore lattices of magnetic ions. We show that disorder can play a crucial role in preventing long-range magnetic order at low temperatures, and instead induces a strongly-fluctuating Coulomb spin liquid with defect-induced frozen magnetic degrees of freedom.