Disorder-induced phases in non-Kramers rare-earth pyrochlores.

The 2-in-2-out local constrain in spin ices brings about a manifold of degenerate ground states, with spin correlations giving rise to emergent magnetostatics. In rare earth pyrochlores, the introduction of transverse fields in the Hamiltonian offers a possible route to promote quantum fluctuations leading toward the quantum spin ice (QSI) state, a lattice analogue of quantum electrodynamics. It has been proposed theoretically, and argued experimentally, that in the case of non-Kramers magnetic ions, non-magnetic disorder can generate such transverse fields, allowing the exploration of so-called disordered-induced quantum spin liquids (QSLs).

Such physics seems to be at work in Tb₂Hf₂O₇ where experimental investigation revealed the stabilization of a spin liquid state stemming from the disorder present in the crystal. We present a detailed structural analysis based on neutron pair distribution function, which we use to quantitatively relate to the magnetic properties of Tb₂Hf₂O₇. For instance, we show how the big box modelling of such a disordered system can be used to understand the crystal electric field spectrum.

A possible route to control the density of non-magnetic disorder (oxygen Frenkel pair defects) is to vary the chemical properties of the B-site cation. We present results of AC-susceptibility and neutron spin-echo showing that the partial substitution of Ti⁴⁺ using a larger and less electronegative cation in Ho₂Ti₂O₇ allows tuning the dynamics of this prototypical spin ice.

Finally, we show how single crystal neutron diffuse scattering, related to structural defects, differs in samples of Pr₂Hf₂O₇ and Pr₂Zr₂O₇ that also display differences in their low temperature magnetic behaviors.