Magnetism at the Edge of Stability Probed with Advanced Muon Spectroscopy
Lead Research Organisation:
University of Oxford
Department Name: Oxford Physics
Abstract
Magnetism in materials is one of the oldest scientific discoveries, but is still far from being completely understood. I am proposing to use new and, as yet, completely unexploited experimental techniques to learn about materials where the magnetic interactions act to make the magnetic state stable; but only just stable! This means that small changes in the environment can cause dramatic changes in the magnetic properties. I propose to investigate these effects with muons. These are subatomic particles that may be implanted into materials where they act as microscopic magnetometers. In a solid, the atoms interact with each other through electrostatic forces between the electrons attached to the atoms. These forces are short range, so an atom is only on speaking terms with it neighbours. Electrons have a property known as spin, which is best thought of as an arrow attached to each electron. At high temperatures the spins on are randomly aligned, but as we reduce the temperature the electrostatic interactions cause the spins to line up with those of their neighbours. Amazingly, short range forces act to make all of the spins in the solid align. From local atoms speaking only to their neighbours, we have created collective action in the form of long-range order. Long-range order is seen throughout nature and the theory of such order explains the clustering of galaxies, the distribution of earthquakes, the spread of disease and even the very existence of the universe itself. A crucial factor in magnetism is the way in which interactions pass information (like line up spins this way'') between atoms. There may be situations where the interactions only act along a line of atoms (one-dimension) or in a plane of atoms (two-dimensions). This dimensionality is at the root of the behaviour of all long-range ordered systems. This is far from being a theoretical abstraction - it is possible to make 1D and 2D materials in the laboratory. Here, molecules are often employed as the building blocks of the materials rather than individual atoms. These molecular magnets are self assembled nanostructures, formed from networks of magnetic metal atoms which are linked together using organic molecules. The great number of organic molecules allow us to make small changes to the structure of magnets leading to tailor made materials with desired properties.Another important class of magnet results when messages sent to an atom conflict, a phenomenon known as frustration . If each atom is receiving conflicting instructions as to which direction is should align, it is not obvious which it will obey. It is therefore difficult to predict the ground state of the system (that is, the state adopted at very low temperatures). The investigation of such systems provide insights into why materials adopt the states that they do. Why should a certain material be a ferromagnet while another stays disordered down to low temperature? We can even gain an insight into why the solid state itself is stable.I propose to carry out research into frustrated and low-dimensional materials using muons. These are a subatomic particle that may be implanted in a material in order to measure the internal magnetic field. Investigations with muons reveal properties invisible to other, more conventional, experimental techniques. Both frustrated and low-dimensional materials tend to exist at the edges of stability, so that small changes in their external environment lead to dramatic changes in their behaviour. This means that experiments where small perturbations are applied to on of these magnets tend to yield much interesting information about their behaviour. New experimental techniques have recently been developed where perturbations may be applied and simultaneous measurements made with muons. These, as yet, have been completely unexploited in front line research and it is their first deployment that forms the basis of my work.
People |
ORCID iD |
Tom Lancaster (Principal Investigator) |
Publications
Manson JL
(2011)
[Cu(HF2)2 (pyrazine)]n: a rectangular antiferromagnetic lattice with a spin exchange path made up of two different FHF- bridges.
in Angewandte Chemie (International ed. in English)
Manson JL
(2012)
[Ni(HF2)(3-Clpy)4]BF4 (py = pyridine): evidence for spin exchange along strongly distorted F···H···F- bridges in a one-dimensional polymeric chain.
in Inorganic chemistry
Berlie A
(2013)
A muon spin relaxation study of the metal-organic magnet Ni(TCNQ)2
in Journal of Applied Physics
Lancaster T
(2013)
Another dimension: investigations of molecular magnetism using muon-spin relaxation
in Physica Scripta
Lapidus SH
(2013)
Antiferromagnetic ordering through a hydrogen-bonded network in the molecular solid CuF2(H2O)2(3-chloropyridine).
in Chemical communications (Cambridge, England)
Drew AJ
(2009)
Coexistence of static magnetism and superconductivity in SmFeAsO(1-x)F(x) as revealed by muon spin rotation.
in Nature materials
Pitcher MJ
(2010)
Compositional control of the superconducting properties of LiFeAs.
in Journal of the American Chemical Society
Parker DR
(2010)
Control of the competition between a magnetic phase and a superconducting phase in cobalt-doped and nickel-doped NaFeAs using electron count.
in Physical review letters
Lancaster T
(2014)
Controlling Magnetic Order and Quantum Disorder in Molecule-Based Magnets
in Physical Review Letters
Lord JS
(2011)
Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source.
in The Review of scientific instruments
Goddard PA
(2012)
Dimensionality selection in a molecule-based magnet.
in Physical review letters
Pratt F
(2014)
Dipolar ordering in a molecular nanomagnet detected using muon spin relaxation
in Physical Review B
Burrard-Lucas M
(2013)
Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer.
in Nature materials
Claridge JB
(2009)
Frustration of magnetic and ferroelectric long-range order in Bi(2)Mn(4/3)Ni(2/3)O(6).
in Journal of the American Chemical Society
Wright J
(2012)
Gradual destruction of magnetism in the superconducting family NaFe 1 - x Co x As
in Physical Review B
Salman Z
(2009)
HiFi-A new high field muon spectrometer at ISIS
in Physica B: Condensed Matter
Schlueter JA
(2012)
Importance of halogen···halogen contacts for the structural and magnetic properties of CuX2(pyrazine-N,N'-dioxide)(H2O)2 (X = Cl and Br).
in Inorganic chemistry
Manson JL
(2012)
Influence of HF2- geometry on magnetic interactions elucidated from polymorphs of the metal-organic framework [Ni(HF2)(pyz)2]PF6 (pyz = pyrazine).
in Dalton transactions (Cambridge, England : 2003)
Yan B
(2014)
Lattice-site-specific spin dynamics in double perovskite Sr2CoOsO6.
in Physical review letters
Lewtas H
(2010)
Local magnetism and magnetoelectric effect in HoMnO 3 studied with muon-spin relaxation
in Physical Review B
Sheckelton J
(2014)
Local magnetism and spin correlations in the geometrically frustrated cluster magnet LiZn 2 Mo 3 O 8
in Physical Review B
Lancaster T
(2011)
Local magnetism in the molecule-based metamagnet [Ru 2 (O 2 CMe) 4 ] 3 [Cr(CN) 6 ] probed with implanted muons
in Physical Review B
Pratt FL
(2013)
Low-field superconducting phase of (TMTSF)2ClO4.
in Physical review letters
Description | We have developed, characterized and investigated many new materials which show exotic quantum mechanical behaviour. Using a technique known as muon-spin relaxation we have identified transitions to long-range magnetic order, investigated dynamics and studied the interactions of these systems. In particular, we have used new experimental methods involving muons and combined them with highly tuneable molecular materials to create a range of new results. Highlights include the manipulation of the dimensionality of materials - turning them from two-dimensional to one-dimensional and also from one-dimensional to (effectively) zero dimensional! |
Exploitation Route | We have shown how muons may be used to study a variety of phenomena using applied magnetic and electric fields and the application of pressure. This will allow other researchers to use these techniques in similar areas. We have demonstrated the use of molecular materials in making tuneable magnets whose properties may be manipulated on a quantum mechanical level. This should allow further materials to be developed using the principles we have followed. |
Sectors | Chemicals |
Description | Inspired by some of these results obtained during a fellowship, designed to accelerate my career path, I have cowritten a textbook on the theory underlying this physics in order to advertise it to a wider audience. I am also collaborating with artists on a project to further communicate the principles behind this and future work. |
First Year Of Impact | 2014 |
Sector | Education |
Impact Types | Cultural |