Harnessing disorder to tune, tailor and design classical and quantum spin liquids

Lead Research Organisation: University of Cambridge
Department Name: Physics

Abstract

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Description (for the experimental part of the proposal, please see related reporting at RHUL and OXFORD)

We gained a more in-depth understanding of the role of disorder in the form of oxygen deficiency in Ho-based pyrochlores. We characterised the effects at the microscopic, single-ion level. Characterisation of the macroscopic / collective behaviour is ongoing.

We developed an understading of the nature of chemical composition disorder in Pr2ScNbO7. Comparison between theory and experiment allowed to understand the charge order / disorder in the distribution of Sc and Nb ions. This lead to crystallographic modelling and thence modelling of the magnetic properties of the Pr ions. Two different environments were identified, forming short quasi-1D chains. Preliminary results suggest that the one of the envoronments may be non-magnetic. Modelling of the resulting collective behaviour and furhter comparison with experiment is ongoing.

Theoretical work on magnetic correlations in spin ice materials lead to the discovery of an emergent fractal in a clean system, which solves a long standing puzzle in the out of equilibrium behaviour and magnetic noise of these systems.
Exploitation Route The discovery of the emergent fractal is a seminal result that is receiving much attention in the news. It is of interest to a broad range of scientific communities. Moreover, the idea of significant slowing down and temporal scaling behaviour in materials that does not originate from disorder but rather from internal correlations that mimic a percolation process may have important implications for people working on spin ice materials and out of equilibrum phenomena and glassiness in general.
Sectors Education,Other
 
Title Data associated with "Free-spin dominated magnetocaloric effect in dense Gd3+ double perovskites" 
Description Data associated with the publication 'Free-spin dominated magnetocaloric effect in dense Gd3+ double perovskites.' Frustrated lanthanide oxides with dense magnetic lattices are of fundamental interest for their potential in cryogenic refrigeration due to a large ground state entropy and suppressed ordering temperatures, but can often be limited by short-range correlations. Here, we present examples of frustrated fcc oxides, Ba2GdSbO6 and Sr2GdSbO6 and the new site-disordered analog Ca2GdSbO6 ([CaGd]A[CaSb]BO6), in which the magnetocaloric effect is influenced by minimal superexchange (J1 ~ 10 mK). We report on the crystal structures using powder x-ray diffraction and the bulk magnetic properties through low-field susceptibility and isothermal magnetization measurements. The Gd compounds exhibit a magnetic entropy change of up to -15.8 J/K/molGd in a field of 7 T at 2 K, a 20% excess compared to the value of -13.0 J/K/molGd for a standard in magnetic refrigeration, Gd3Ga5O12. Heat capacity measurements indicate a lack of magnetic ordering down to 0.4 K for Ba2GdSbO6 and Sr2GdSbO6, suggesting cooling down through the liquid 4-He regime. A mean-field model is used to elucidate the role of primarily free spin behavior in the magnetocaloric performance of these compounds in comparison to other top-performing Gd-based oxides. The chemical flexibility of the double perovskites raises the possibility of further enhancement of the magnetocaloric effect in the Gd3+ fcc lattices. Please see readme file for details on contents of folders 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/337073