A New SQUID Magnetometer for Extreme Conditions Research

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Engineering

Abstract

Magnetic materials are widely used in everyday life, from fridge magnets to recording media. Measuring the response of a material (the magnetisation) to an external magnetic field is essential for studies of magnetic and related materials. Magnetisation is measured by magnetometers and the most sensitive of these are based on Superconducting Quantum Interference Devices (SQUIDs). The University of Edinburgh contains groups working on a variety of materials such as multiferroic and magnetoresistive oxides, molecular magnetic solids, organic and single molecule magnets, frustrated magnetism, superconductors and quantum critical phenomena, and magnetic geomaterials. This research contributes to the discoveries of a range of new materials and greater understanding of fundamental physical and mineralogical processes. A new SQUID magnetometer is needed to facilitate our research, both to replace a 15-year old machine that is no longer reliable, and to extend possibilities for research at higher temperatures (up to 800 K) and magnetic fields (up to 7 T).Applying pressure to tune and change magnetic properties is an additional key feature of this proposal. The SQUID magnetometer will be located in our Centre for Science at Extreme Conditions (CSEC), where local expertise will be used to design and construct new pressure inserts. A novel, double-walled piston cylinder cell will enable extend the maximum pressure for this type of insert up to 3 GPa(approximately 30,000 atm.). We will also design and build a pioneering opposed-anvil cell using moissanite (silicon carbide) anvils, which are a good and inexpensive alternative to diamonds. This will enable state-of-the-art high pressure SQUID magnetometry to be performed at pressures of up to 5 GPa.

Publications

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Bradley JM (2010) MCD spectroscopy of hexanuclear Mn(III) salicylaldoxime single-molecule magnets. in Dalton transactions (Cambridge, England : 2003)

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De Vries MA (2010) Valence bond glass on an fcc lattice in the double Perovskite Ba2YMoO6. in Physical review letters

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De Vries MA (2008) Magnetic ground state of an experimental S=1/2 kagome antiferromagnet. in Physical review letters

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De Vries MA (2008) Magnetic ground state of an experimental S=1/2 kagome antiferromagnet. in Physical review letters

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Ferguson A (2008) Synthesis and characterisation of a Ni4 single-molecule magnet with S4 symmetry. in Dalton transactions (Cambridge, England : 2003)

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Galloway KW (2008) Cobalt(II) citrate cubane single-molecule magnet. in Inorganic chemistry

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Galloway KW (2010) Slow magnetic relaxation in a 3D network of cobalt(II) citrate cubanes. in Dalton transactions (Cambridge, England : 2003)

 
Description The project is focused on developing instrumentation and techniques for measuring one of the key properties of materials - magnetic susceptibility - at the extremes of temperatures, magnetic fields and pressures, and applying them to various systems.



At the core of the project is the Magnetic Property Measurement System (MPMS) which was acquired in the early stage of the project. This is a commercially available magnetometer capable of generating magnetic fields of up to 7 Tesla and operating in the temperature range of 1.85 - 800 Kelvin. However, MPMS does not have a built-in option for studying samples under high pressure and the major objective of this project was to design, build, test and use the device which would generate high pressures on the sample (pressure cell) and work seamlessly with the magnetometer.



In the course of the project we developed a miniature diamond anvil cell (DAC) with several features incorporated into the design which make it particularly suitable for use with MPMS. The new DAC is approximately a cylinder 7 mm long and 7 mm in diameter and weighs only 1.5 g. The pressure cell is made of non-magnetic materials and has the shape which is symmetric with respect to the sample. This reduces the background from the pressure cell and improves the sensitivity of the measurements that can be perfomed in the new DAC. Using this pressure cell we have conducted measurements on not just strongly magnetic materials such as superconductors and ferromagnets but also on systems which order antiferromagnetically. In the proposal we planned to develop a pressure cell that would be capable of generating pressures up to 5 gigapascals. The pressure cell we have designed generates the pressure in excess of 10 GPa and has already attracted a lot of interest from other research groups.



A number of materials with magnetic properties which are of great interest either for fundamental science or for applications in electronics have been studied at both ambient and high pressure. These include such systems as multiferroic and magnetoresistive oxides, molecular magnetic solids, organic and single molecule magnets as well as the materials which exhibit frustrated magnetism, superconductivity and quantum critical phenomena with several examples provided below:



- In the single-molecule magnet Mn12-acetate pressure-induced switching of a fast-relaxing single-molecule magnet to a slow-relaxing isomer was observed for the first time.



- Unconventional magnetic ordering has been found in the double perovskite Ba2YMoO6. No magnetic order was observed down to 2 K while the Weiss temperature was found to be around 160 K. This phenomenon was attributed to the geometric frustration in the lattice of edge-sharing tetrahedra - a rare example of a valence bond glass.



- In spin=1/2 kagome Heisenberg antiferromagnet ZnxCu4-x(OH)6Cl2 it has been found that the ground state is a gapless spin liquid in which unpaired spins give rise to a macroscopically degenerate ground state manifold with increasingly glassy dynamics as Zn content is lowered. At the time of this report the publication of this study of the zinc paratacamite has already attracted 29 citations.



- A suppression of superconductivity in the rare-earth RFeAsO1-xFx (R=Tb, Dy, and Ho) materials has been found with the maximum critical temperature Tc decreasing from 51 K for R=Tb to 36 K for HoFeAsO0.9F0.1. This suppression is driven by a decrease in the Fe-As-Fe angle below an optimum value of 110.6 degrees.



In conclusion, we would like to note that the experimental facilities developed under this grant and the studies conducted within this project pave the way for future discoveries of new materials and greater understanding of fundamental physical processes. There has been further research support that has arisen as a result of the work reported here.
Exploitation Route There are two major outcomes of this project.

The first one is the creation of the internationally unique facility for measuring magnetic properties of materials under three thermodynamic parameters - temperature, pressure and magnetic field. This is now registered as a Small Research Facility (SRF) and has been and will be used for studies of various materials by both industrial and academic users.

The second outcome is the development of novel high-pressure cells for use with commercially available magnitometers. These designs have attracted attention of the international community and are being commercialised by the University of Edinburgh.
Sectors Education,Manufacturing, including Industrial Biotechology,Other

 
Description The project created internationally-leading instrumentation and innovative methodologies for measuring magnetic properties of materials at the extremes of pressure, temperature and magnetic field. The facility was used by a number of researchers from across the UK and a number of researchers, postgraduate and undergraduate students has been trained on the state of the art techniques. Several types of custom designed high-pressure cells were developed and tailored for use with particular materials, e.g. large-volume piston-cylinder cells for weakly magnetic materials, very high pressure opposed-anvil cells for use with strongly magnetic materials, etc. Additional research income was raised through commercialisation of the pressure cells.
First Year Of Impact 2008
Sector Creative Economy,Electronics,Manufacturing, including Industrial Biotechology,Other
Impact Types Economic

 
Description EPSRC
Amount £434,080 (GBP)
Funding ID EP/H004106/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start  
 
Description EPSRC
Amount £434,080 (GBP)
Funding ID EP/H004106/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start  
 
Description EPSRC
Amount £897,965 (GBP)
Funding ID EP/G015333/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start  
 
Description EPSRC
Amount £897,965 (GBP)
Funding ID EP/G015333/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start