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

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

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Title High pressure floating zone method 
Description We have recently installed a piece of equipment to prepare crystals called an optical floating-zone furnace. This type of furnace uses light as a heat source reach up to 2800oC and mirrors to focus the light energy onto a bar of material in order to melt it. By scanning the molten ("floating") zone slowly along the bar one can grow a crystal as the liquid solidifies. The type of furnace is a new design of optical floating-zone furnace which allows the growth process to take place in a high pressure (up to 300 times atmospheric pressure) mixture of oxygen and argon gas. The use of a high gas pressure makes it possible to grow crystals of certain materials which cannot be grown under normal conditions. The equipment is the first of its type in Europe, to grow a broad range of materials, ranging from metal oxides that exhibit desirable magnetic, electronic and superconducting properties, through systems with novel quantum phases to materials that offer considerable promise for use in energy, optoelectronic and information storage applications. we have a programme of crystal growth with the new equipment to provide samples which will ensure the success of quantum and functional materials research in Oxford and other UK universities, and at the national research facilities such as the Diamond Light Source and ISIS Facility on the Harwell campus. 
Type Of Material Improvements to research infrastructure 
Year Produced 2021 
Provided To Others? Yes  
Impact We have commissioned the equipment and grown several standard materials. Our crystal growth program was delayed due to COVID, but recently we have grown some new materials and studying its properties. 
 
Description Harnessing disorder to tune, tailor and design classical and quantum spin liquids 
Organisation Royal Holloway, University of London
Country United Kingdom 
Sector Academic/University 
PI Contribution This grant involved a collaboration project between the synthesis group here at Oxford, a neutron scattering experimental group between Royal Holloway University and the ILL facility in Grenoble France, and a condensed matter theory group at Cambridge. We are preparing samples for the collaboration, perform the crystallographic analysis and perform some preliminary measurements where relevant. In addition to this collaboration work we have also sought to prepare additional materials, both new and pre-existing with a focus on chemical and magnetic disorder. We have also begun independent magnetometry and neutron measurements, some chemically disordered pyrochlores.
Collaborator Contribution My collaborators at Royal Holloway University and ILL have completed two neutron experiments to study the disorders in the Pr2ScNbO7 and Y2-xHoxTi2O7 systems and they are analyzing the recent data. They also secured a muon beam time at Canadian neutron source to study the Y2-xHoxTi2O7 system at mK temperature range. My Cambridge University collaborator is working on the theoretical modelling.
Impact Cambridge collaborator has developed theoretical expertise to model and understand local spin environments and exchange interactions which are an important starting point to investigate strain and chemical substitution effects. They are working on internal fields in spin ice materials resulted in the proposal of a novel and more efficient approach to study quantum spin ice (QSI) candidate systems that they only started to explore, which provides a promising route to study the effect of disorder. In parallel, they started to investigate the role of thermal as well as quenched disorder in toy models for quantum spin liquids. Recently they have developed and tested a new numerical approach to investigate QSI in the semiclassical limit, which can be used to look at the effect of disorder and distortion on the emergent QED excitation spectrum and transport properties. My Royal Holloway collaborator is analyzing the recent experimental data and comparing the disorder with the recently developed toy model.
Start Year 2020
 
Description Magnetic monopole density and antiferromagnetic domain control in spin-ice iridates 
Organisation University of Warwick
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution I prepared high quality Ho2Ir2O7 single crystals for the first time. Our Warwick collaborator measured the resistivity at different applied fields and our Cambridge collaborator developed the theoretical work to study the magnetic monopole density.
Collaborator Contribution Magnetically frustrated systems provide fertile ground for complex behaviour, including unconventional ground states with emergent symmetries, topological properties, and exotic excitations. A canonical example is the emergence of magnetic-charge-carrying quasiparticles in spin-ice compounds. Despite extensive work, a reliable experimental indicator of the density of these magnetic monopoles is yet to be found. Using measurements on single crystals of Ho2Ir2O7 combined with dipolar Monte Carlo simulations, we show that the isothermal magnetoresistance is highly sensitive to the monopole density. Moreover, we uncover an unexpected and strong coupling between the monopoles on the holmium sublattice and the antiferromagnetically ordered iridium ions. These results pave the way towards a quantitative experimental measure of monopole density and demonstrate the ability to control antiferromagnetic domain walls using a uniform external field, a key goal in the design of next-generation spintronic devices.
Impact https://doi.org/10.1038/s41467-022-27964-y
Start Year 2021
 
Description New materials discovery using high pressure floating-zone furnace 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact I have introduced the recently installed EPSRC funded 300bar high pressure floating-zone furnace capabilities at the American Crystal Growth meeting. It was well received by the industrial representatives and general public.
Year(s) Of Engagement Activity 2021