Quantum Critical Behaviour in Spin and Charge Ordered Systems
Lead Research Organisation:
University of Cambridge
Department Name: Physics
Abstract
Quantum properties of SrTiO3, such as its Incipient ferroelectricity and tendency to remain paraelectric down to the lowest temperatures have fascinated condensed matter physicists for several decades. At these low temperatures however SrTiO3 and similar materials lie close to a transition to a displacive ferroelectric phase in their phase diagrams. Such materials offer good opportunities for studying the effects of tuning the material away from this zero-temperature, quantum critical transition by the varying of an external parameter. The application of hydrostatic pressure tunes SrTiO3 away from the region in which quantum fluctuations dominate and, through precise dielectric measurement, allows for a large region of the phase diagram to be mapped and for the observation of possible emergent phases. Measurements taken in this manner have also shown evidence for Quantum Criticality and evolution of a new possible phase boundary. The techniques used should also allow study of complex behaviour in systems with two or more coupled order parameters, such as the multiferroic EuTiO3.
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509620/1 | 01/10/2016 | 30/09/2022 | |||
| 1805371 | Studentship | EP/N509620/1 | 01/10/2016 | 30/09/2020 | David Jarvis |
| Description | Low-dimensional magnetic materials are of current interest for both understanding of the fundamental physics involved and for applications in future technologies. Work associated with this award used pressure as a tuning parameter to explore new structural, electrical and magnetic behaviour in the family of magnetic materials MPS3 (M=Fe, Ni, Mn). This work has shown for the first time that these materials undergo structural changes as they are put under extreme pressure (hundreds of thousands of atmospheres) and become more three-dimensional. This has been achieved through record high-pressure x-ray experiments at the Diamond Light Source, UK with consistent collaboration with scientists at that facility. We have also found that alongside these transitions, the materials go from being strongly electrically insulating to metallic under pressure. These types of insulator-to-metal transitions are of great interest in the field and this work helps us to understand how these occur. Previous work on this family of materials has been generally isolated to individual materials. By performing a unified programme of measurements of a wider range of properties we have begun to establish a common pattern of behaviour for the first time which may be expanded to other similar structures. An open question in this area which has been addressed is what happens to the magnetism in FePS3 as it goes from insulator to metal. Answering this has required international collaboration with colleagues at the Institut Laue Langevin (ILL), France and Sorbonne University, France to develop new methods for high pressure magnetic measurements at the ILL. As part of this study we set a new record for high pressure at this international research facility and were able to find that the new metallic phase of FePS3 is not non-magnetic as predicted by other indirect measurements, but has a new magnetic order which persists up to much higher temperatures. This newly revealed structure is dissimilar to anything else reported in systems like this and has allowed for new theoretical modelling to explore its origin. This is again important for understanding how magnetism works in this type of material which has implications for their use in future battery and device technologies. We have observed the suppression of the magnetic entropy change, an important property for cooling applications, in quantum paraelectric EuTiO3 under pressure. This begins to explain how materials with both magnetic and electrical order respond when both are strongly related to the crystal structure. The outcomes of this project have application for the technique of magnetic refrigeration which is used extensively in research and is developing commercially. As part of this project, in collaboration with colleagues at the University of Warwick, UK software has been developed for background subtraction and fitting which is important for magnetic measurements in research. This software is now published, licensed and available to other academics and has seen significant interest. |
| Exploitation Route | The observations we have made of the high pressure magnetic structure of FePS3 invites similar experiments to be performed on related compounds. The similar FePSe3 has been observed to become superconducting under pressure and using the high pressure techniques this project has helped to develop, the magnetism of this material as it becomes superconducting may now be measured. This will help to explore how unconventional superconductivity emerges in magnetic compounds which is of theoretical interest. Furthermore, out work has gone a long way towards developing a general model for the behaviour of this type of low-dimensional magnetic material as it is tuned towards higher dimensionality. Future experiments will be able to build on and expand this work. This will have impact for their application and design in battery technologies, solar cells and photocatalysis. The software developed for magnetic measurement fitting is widely applicable in a range of fields and should be of use to researchers internationally. We have already had communication from groups who are making use of this outcome. The magnetic study under pressure of EuTiO3 should serve as an effective starting point for future work to explore how its magnetic and electric properties may be mutually controlled, as well as encouraging its use in the field of magnetic refrigeration. |
| Sectors | Chemicals,Electronics,Energy,Manufacturing, including Industrial Biotechology |
| Description | Neutron Studies of Emergent Magnetic Phases in Pressure-Tuned van der Waals Magnets |
| Organisation | Institut Laue–Langevin |
| Country | France |
| Sector | Academic/University |
| PI Contribution | Proposal development and Experiment Design followed by the actual experimentation, analysis and paper preparation. |
| Collaborator Contribution | Full technical support, scientific input, materials preparation and publication preparation. |
| Impact | Emergent Magnetic Phases in Pressure-Tuned van der Waals Antiferromagnet FePS3 By: Coak, Matthew J.; Jarvis, David M.; Hamidov, Hayrullo; et al. PHYSICAL REVIEW X Volume: ? 11 Issue: ? 1 Article Number: 011024 Published: ? FEB 5 2021 |
| Start Year | 2018 |
| Title | SquidLab |
| Description | An open-source program free to download for academic use with a full user-friendly graphical interface for performing flexible and robust background subtraction and dipole fitting on magnetization data. For small signals in magnetisation measurements with large backgrounds from sample environments, this software allows for the determination of sample magnetisation in a range of configurations using established techniques. |
| Type Of Technology | Software |
| Year Produced | 2020 |
| Open Source License? | Yes |
| Impact | As of March 2021, the software has 406 downloads, and is in use by several research groups for the treatment of high pressure magnetisation experiments. The routines the software offers make this background subtraction significantly easier than performing it manually and it allow for quick comparisons of different possible fitting methods to the data to extract the desired physical parameters. |
| URL | http://wrap.warwick.ac.uk/129665/ |
| Description | Marie Curie Symposium |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Undergraduate students |
| Results and Impact | Invited by the Marie Curie study association at Radboud University of Nijmegen to share my research in a talk as part of a symposium on the theme of magnetism. Targeted mainly at undergraduate/masters students with some involvement from PhD students and faculty. Presented my research methods and results over 45 minutes and took questions. Several questions on high-pressure physics which was not a well known area by many present. |
| Year(s) Of Engagement Activity | 2021 |
| URL | https://symposium.marie-curie.nl/index.php?page=intro |