The group welcomes three a new PhD students.
Manisha Islam who joins us from University of York and will work with Oleg Petrenko, Shroya Vaidya who completed a MPhys degree here at the University of Warwick and is supervised by Paul Goddard, and George Wood, who is working with Geetha Balakrishnan after completing his first degree at the University of Bristol.
December 2019 - Farewell to Santosh Kumar
The group went for a meal in Leamington Spa to wish farewell to Dr Santosh Kumar. Santosh has completed his 4 year post-doc working as part of the PRETAMAG project.
Santosh has returned to India and is currently working at the TIFR Mubai as a Visiting Research Fellow before taking up a post as an Assistant Professor at IIT Dharwad.
September 2019 - PhD for Dan Mayoh
Congratulations to Dan Mayoh who has completed his doctorate. Dan’s work was supervised by Martin Lees and involved in-house measurements, and muon spectroscopy and neutron scattering experiments performed at ISIS, studying the properties of some novel noncentrosymmetric superconductors.
Dan's thesis, Experimental Studies of Noncentrosymmetric Superconductors can be downloaded from his web page.
June 2019 - PhD for Dr Simon Riberolles
March 2019 - Welcome to Dr Matt Coak
The group welcomes Dr Matthew Coak. Matt joins the group having completed a PhD at Cambridge supervised by Dr Siddharth Saxena and and a first postdoctoral position in the Emergent Phenomena Group of the IBS Centre for Correlated Electron Systems at Seoul National University, under Prof Je-Geun Park. Matt will work with Dr Paul Goddard studying the properties of quantum systems at low-temperature, and under high pressure and magnetic field.
July 2018 - PhD for Jamie Brambleby
Congratulations to Jamie Brambleby on successfully defending his PhD thesis. His work was supervised by Paul Goddard.
Jamie's thesis is entitled Quantum magnetism in coordination polymers. The thesis can be downloaded from WRAP here.
December 2017 - PhD for Daniel Brunt
Congratulations to Dan Brunt who has completed his doctorate. Dan, whose PhD work was supervised by Oleg Petrenko, used in-house measurements and neutron scattering experiements performed at ISIS and the ILL to study the magnetic properties of some rare earth tetraborides.Dan's thesis which is entitled Magnetic properties of frustrated Shastry-Sutherland magnets; rare earth Tetraborides can be downloaded from his web page or from Warwick WRAP.
December 2017 - Award for the best paper published by a research fellow in the Physics Department in 2017
In recognition of the excellent contribution that postdocs make to the research in the Physics Department at the University of Warwick, the Head of Department, Prof. David Leadley, has initiated an award for the best paper published by a research fellow this year. Chris Patrick and Santosh Kumar from PRETAMAG have jointly won the first award for their paper “Rare-earth/transition-metal magnetic interactions in pristine and (Ni,Fe)-doped YCo5 and GdCo5” Phys.Rev.Materials 1, 02411 (2017). The paper was consider to be well-written and to convey clearly the outcomes of the joint theory-experimental activities. The interpretation of results and insight into the materials that this joint approach has enabled was particularly commended.
July - August 2017 - Three Visitors from Japan
Over the last month, Prof. Geetha Balakrishnan and the group have hosted three separate visits by Japanese scientists.
Dr. Kaya Kobayashi from Okayama University has been working with Dr Ales Stefancic growing some new superconducting single crystals.
Prof. Toshiro Takabatake from Hiroshima University, a world leading expert in crystal growth and especially heavy fermions, Kondo insulators, thermoelectrics and related materials, visited us to discuss joint projects that included a reciprocal visit by Dan Mayoh to Hiroshima in August.
January 2017 - PhD for Joel Barker
Congratulations to Joel Barker on successfully defending his PhD thesis. Joel, whose PhD work was jointly supervised by Don Paul at Warwick and Aidy Hillier at ISIS-RAL, has been studying the physics of non-centrosymmetric superconductors with a particular emphasis on the use of muon spectroscopy.
Joel's thesis which is entitled Muon Studies of Unconventional Superconductors can be downloaded from his web page.
January 2017 - Welcome to Dr Ales Stefancic and Marta Crisanti
We welcome Dr Ales Stefancic who has recently joined the Group as Post-Doctoral Research Assistant (PDRA) studying the physics of Skyrmionic materials. Ales will work here at Warwick as part of a larger EPSRC Programme Grant Skyrmionics: From Magnetic Excitations to Functioning Low-Energy Devices involving the Universities of Durham, Cambridge, Southampton, and Oxford. The work here at Warwick will be led by Prof. Geetha Balakrishnan.
We also welcome Marta Crisanti who joins us as a Warwick/ILL Ph.D. student working under the joint supervision of Don Paul (Warwick) and Robert Cubitt who works in the Large Scale Structures Group at the ILL. Marta will also be working on Skyrmionic materials, focussing on the use of small angle neutron scattering.
Oxides containing 5d ions, particularly Ir4+, offer possibilities for interesting spin-orbit and spin-lattice coupling effects. In these materials, the energy scales for spin-orbit interactions, Coulomb repulsion, and crystalline-electric fields can be very similar. Competition between these three energies can result in exotic magnetic states such as spin-orbit entanglement, extreme magnetic exchange anisotropy leading to, for example, a Kitaev spin liquid, and spin-orbit entangled Mott insulating behaviour.
Using experiments performed at the National High Magnetic Field Laboratory, a team from the USA, UK and South Korea (including Paul Goddard at Warwick) have observed extremely large coercive magnetic fields of up to 55 T in Sr3NiIrO6 and 52 T in Sr3CoIrO6, with switched magnetic moments of ≈ 1μB and 3μB per formula unit, respectively. Rather than the switching of magnetic domains, which is the cause of the coercive fields of traditional ferromagnets, the large hysteresis observed in our materials evolves out of a frustrated, antiferromagnetic ground state that incorporates an entangled spin-orbit state on the 5d ion.
Magnetic properties of Sr3NiIrO6 and Sr3CoIrO6: Magnetic hysteresis with coercive fields of up to 55 T, J. Singleton, J. W. Kim, C. V. Topping, A. Hansen, E.-D. Mun, S. Chikara, I. Lakis, S. Ghannadzadeh, P. Goddard, X. Luo, Y. S. Oh, S.-W. Cheong, and V. S. Zapf, Physical Review B 94, 224408 (2016).
December 2016 - Welcome to Dr Kathrin Gotze and Dr Robert Williams
Kathrin previously worked in the High Magnetic Field Laboratory in Dresden, while Rob has just completed his PhD at Durham University. Both Robert and Kathrin will be working on an ERC funded project entitled Quantum Materials Under Extreme Conditions led by Dr Paul Goddard.
November 2016, ERC Grant - Quantum Materials Under Extreme Conditions
Dr Paul Goddard has been awarded an ERC Consolidator Grant with maximum ERC funding of 1.84 million euros.
The EXTREMEQUANTUM project will significantly advance our knowledge of interacting quantum systems.
A paper has been published in Nature Physics that reveals that magnetic fragmentation occurs in the spin ice candidate Nd2Zr2O7. The work was carried out in collaboration with colleagues from the CEA in Saclay and the ILL, CEA, and the Institut Neel in Grenoble.
It has recently been suggested that in spin ice, the magnetic moment field can fragment, resulting in a dual ground state consisting of a fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic monopole crystal. Here we show, by means of neutron scattering measurements, that such fragmentation occurs in Nd2Zr2O7. We observe the spectacular coexistence of an antiferromagnetic order induced by the monopole crystallization and a fluctuating state with ferromagnetic correlations.
Experimentally, this fragmentation manifests itself through the superposition of magnetic Bragg peaks, characteristic of the ordered phase, and a pinch point pattern, characteristic of the Coulomb phase. These results highlight the relevance of the fragmentation concept to describe the physics of systems that are simultaneously ordered and fluctuating.
Observation of magnetic fragmentation in spin ice, S. Petit, E. Lhotel, B. Canals, M. Ciomaga Hatnean, J. Ollivier, H. Mutka, E. Ressouche, A. R. Wildes, M. R. Lees, and G. Balakrishnan, Nature Physics 12, 746, (2016).
Also see ILL highlights.
|A paper has been published in Nature Physics that studies the interaction between mononpoles in spin ice. The work was carried out in collaboration with colleagues at UCL - London, Institut Neel - Grenoble, Cardiff and Oxford Universities, and KIT - Japan. Thermal quenches in spin ice are used to prepare metastable populations of bound pairs of positive and negative emergent magnetic monopoles at millikelvin temperatures. The application of a magnetic field results in a universal exponential-root field growth of magnetic current, thus confirming the microscopic Coulomb force between the magnetic monopole quasiparticles and establishing a magnetic analogue of the Poole–Frenkel effect.|
At temperatures above 300 mK, gradual restoration of kinetic monopole equilibria causes the non-Ohmic current to smoothly evolve into the high-field Wien effect for magnetic monopoles, as confirmed by comparison to a recent and rigorous theory of the Wien effect in spin ice. The results extend the universality of the exponential-root field form into magnetism and illustrate the power of emergent particle kinetics to describe far-from-equilibrium response in complex systems.
Experimental signature of the attractive Coulomb force between positive and negative magnetic monopoles in spin ice, C. Paulsen, S. R. Giblin, E. Lhotel, D. Prabhakaran, G. Balakrishnan, K. Matsuhira, and S. T. Bramwell, Nature Physics 12, 661 (2016).
A paper has been published in JACS which reports the accurate electron density distribution and magnetic properties of two metal–organic polymeric magnets. The work is a collaboration with the Universities of Bern, Eastern Washington, Durham, and Oxford, and the high field laboratory in Los Alamos,
The paper combines high-resolution single-crystal X-ray diffraction, DFT calculations, and magnetic studies to characterize the possible magnetic exchange pathways and establish the relationships between the electron (charge and spin) densities and the exchange-coupling constants in both compounds.
Experimental and Theoretical Electron Density Analysis of Copper Pyrazine Nitrate Quasi-Low-Dimensional Quantum Magnets, L. H. R. Dos Santos, A. Lanza, A. M. Barton, J. Brambleby, W. J. A. Blackmore, P. A. Goddard, F. Xiao, R. C. Williams, T. Lancaster, F. L. Pratt, S. J. Blundell, J. Singleton, J. L. Manson, P. Macchi, Journal of the American Chemical Society 138, 2280 (2016).
A paper has been published in Physical Review Letters reporting our discovery of unconventional superconductivity in La7Ir3, one of a new family of noncentrosymmetric superconductors that breaks time reversal symmetry. The study using muon spectroscopy was carried out in collaboration with colleagues from IISER, Bhopal and TIFR, Mumbai in India, and ISIS-RAL.
Unconventional Superconductivity in La7Ir3 Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry, J. A. T. Barker, D. Singh, A. Thamizhavel, A. D. Hillier, M. R. Lees, G. Balakrishnan, D. M. Paul, and R. P. Singh, Physical Review Letters 115, 267001 (2015).
Neutron scattering and magnetization measurements down to 90 mK have been used to determine the magnetic ground state of the spin-ice candidate Nd2Zr2O7. Along with colleagues from Grenoble and Saclay we show Nd2Zr2O7 undergoes a transition at 285 mK towards an all-in–all-out antiferromagnetic state, and establish the H-T phase diagram. We propose that this behaviour results from the peculiar nature of the Nd dipolar-octupolar doublet, revealing the importance of multipolar correlations in pyrochlore oxides.
Fluctuations and All-In All-Out Ordering in Dipole-Octupole Nd2Zr2O7, E. Lhotel, S. Petit, S. Guitteny, O. Florea, M. Ciomaga Hatnean, C. Colin, E. Ressouche, M. R. Lees, and G. Balakrishnan, Physical Review Letters 115, 197202 (2015).
A paper examining the hidden magnetic order in the spin-liquid Gd3Ga5O12 has been published in the journal Science. Along with colleagues based in Oxford, the Niels Bohr Institute Copenhagen, Denmark, ESS Lund, Sweden, and the ILL Grenoble, France the work combines neutron scattering with theory to show that the spin-liquid Gd3Ga5O12 supports hidden order in which multipoles are formed from 10 spin loops.
Hidden order in spin-liquid Gd3Ga5O12, J. A. M. Paddison, H. Jacobsen, O. A. Petrenko, M. T. Fernández-Díaz, P. P. Deen, and A. L. Goodwin, Science 350, 179 (2015).
Please also see ILL Highlights 2015.
A paper demonstrating a new approach that allows air sensitive two-dimensional crystals to be cleaved, transferred, aligned, and encapsulated has been published in the journal Nano Letters. Along with colleagues based in Manchester, Grenoble in France, and Tsukuba in Japan, the work illustrates this technology on black phosphorous and niobium diselenide.
Quality Heterostructures from Two-Dimensional Crystals Unstable in Air by Their Assembly in Inert Atmosphere, Y. Cao, A. Mishchenko, G. L. Yu, E. Khestanova, A. P. Rooney, E. Prestat, A. V. Kretinin, P. Blake, M. B. Shalom, C. Woods, J. Chapman, G. Balakrishnan, I. V. Grigorieva, K. S. Novoselov, B. A. Piot, M. Potemski, K. Watanabe, T. Taniguchi, S. J. Haigh, A. K. Geim, and R. V. Gorbachev, Nano Letters 15, 4914 (2015).
Geetha Balakrishnan and Martin Lees are two Co-Investigators on an EPSRC grant worth £931k to study the physics underlying the principles of design of rare earth - transition metal permanent magnets. The programme will be led by Prof. Julie Staunton and also includes Rachel Edwards here at Warwick.
A paper examining the unconventional Fermi surface in an insulating state in hexaboride SmB6 has been published in the journal Science. Along with colleagues based in Cambridge , the National High Magnetic Field Laboratory in Tallahassee and Los Alamos observation, and the Naval Research Laboratory in Washington DC, the work shows that SmB6 has an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid.
B. S. Tan, Y.-T. Hsu,1 B. Zeng, M. Ciomaga Hatnean, N. Harrison, Z. Zhu, M. Hartstein, M. Kiourlappou, A. Srivastava, M. D. Johannes, T. P. Murphy, J.-H. Park, L. Balicas, G. G. Lonzarich, G. Balakrishnan, and Suchitra E. Sebastian Unconventional Fermi surface in an insulating state, Science 349, 287 (2015).
Geetha Balakrishnan has been awarded a grant of £515k to continue our succcessful Single Crystal Growth programme here at Warwick. The new programme will run until June 2018.
A paper entitled Dispersionless Spin Waves and Underlying Field-Induced Magnetic Order in Gadolinium Gallium Garnet has been published in Physical Review Letters. Oleg Petrenko and Nick d’Ambrumenil based here at Warwick, along with Hannu Mutka and Pascale Deen, have used neutron diffraction and inelastic neutron scattering in high magnetic fields to study the unusual magnetic properties of Gd3Ga5O12. (Also see ESS website highlights).
N. d’Ambrumenil, O. A. Petrenko, H. Mutka, and P. P. Deen, Physical Review Letters 114, 227203 (2015).
October 2014, PhD Graduation - Natalia Parzyk
Congratulations to Natalia Parzyk. Natalia, who has been working on the physics of some unconventional superconductors, has just completed her PhD Natalia who was supervised by Don Paul becomes the latest PhD student to graduate from the Superconductivity and Magnetism Group.
August 2014, Ph.D. Graduation - Robert Cook
Congratulations to Robert Cook. Robert has just completed his Ph.D. under the supervision Martin Lees and Peter Ellis (Johnson Matthey) to become the latest Ph.D. student to graduate from the Superconductivity and Magnetism Group.
A paper has been published in Nature in which angle-resolved quantum oscillation measurements are used to study the normal-state nodal electronic structure in underdoped high-Tc copper oxides. The work was performed at the High Field Laboratory in Los Alamos by Paul Goddard, along with his colleagues Suchitra Sebastian, N. Harrison, F. F. Balakirev, M. M. Altarawneh, Ruixing Liang, D. A. Bonn, W. N. Hardy and G. G. Lonzarich from Cambridge, Los Alamos, Mu’tah Universit in Jordan, and the University of British Columbia in Canada.
Suchitra E. Sebastian, N. Harrison, F. F. Balakirev, M. M. Altarawneh, P. A. Goddard, Ruixing Liang, D. A. Bonn, W. N. Hardy & G. G. Lonzarich, Nature 511, 61 (2014).
July 2014, PhD Graduation - Michael Smidman
Congratulations to Michael Smidman. Michael (who has never looked so smart!) has just completed his PhD under the supervision of Geetha Balakrishnan and become the latest PhD student to graduate from the Superconductivity and Magnetism Group. Please also see news item in June 2015.
Several members of the Group (past and present) attended the 2014 International Conference on Highly Frustrated Magnetism held in Queens College, Cambridge on July 7-11, 2014. Dr. Monica Ciomaga Hatnean and Martin Lees gave presentations. HFM 2014 was co-organised by Dr. Oleg Petrenko.
A Warwick Physics Day on the Latest Developments in Frustrated Magnetism:spin liquids, spin glass, spin ice state was held on Saturday 5 July 2014.
The day was organised by Oleg Petrenko and featured speakers from around the world.
A paper has been published in Angewandte Chemie Int. Ed. describing a new synthesis approach to oxides of ruthenium, including new structures, and materials with unusual magnetic properties. The work was performed by Craig Hiley, a PhD student in the group of Richard Walton, in collaboration with an industrial partner (Johnson Matthey) and co-workers in Physics, as part of an ongoing study into the chemistry of precious-metal containing materials.
C.I. Hiley, M.R. Lees, J.M. Fisher, D. Thompsett, S. Agrestini, R.I. Smith and R.I. Walton, Angew. Chem. Int. Ed. 53, 4423 (2014).
A paper describing a systematic investigation of the magnetic properties of the three-dimensional Kondo topological insulator SmB6 using magnetization and muon-spin relaxation/rotation measurements has been published in Physical Review B. The study was carried out in collaboration with colleagues based at PSI and Zurich in Switerland, and Princeton in the USA.
P. K. Biswas, Z. Salman, T. Neupert, E. Morenzoni, E. Pomjakushina, F. von Rohr, K. Conder, G. Balakrishnan, M. Ciomaga Hatnean, M. R. Lees, D. McK. Paul, A. Schilling, C. Baines, H. Luetkens, R. Khasanov, and A. Amato, Phys. Rev. B 89, 161107(R) (2014).
A paper describing our work on the non centrosymmetric superconductor Re6Zr has been published in Physical Review Letters. The study using muon spectroscopy was carried out in collaboration with colleagues from Kent, Bristol, and ISIS-RAL.
R. P. Singh, A. D. Hillier, B. Mazidian, J. Quintanilla, J. F. Annett, D. McK. Paul, G. Balakrishnan, and M. R. Lees, Phys. Rev. Lett. 112, 107002 (2014).
Oleg Petrenko has been appointed Chairman of the Single Crystal Diffraction, Instrument Scientific and Advisory Technical Panel (STAP) at the European Spallation Source (ESS). The STAP consist of experts from Europe and around the world, contributing their knowledge and experience to help design and build a single-crystal diffractometer at the ESS.
Mo Saghir, Martin Lees, and Geetha Balakrishnan attend the APS March meeting in Denver, Colorado. The meeting featured presentations on all aspects of Condensed Matter Physics including our own work on topological insulators and exotic superconductors.
February 2014, International Workshop on Frustration and Topology in Condensed Matter Physics, Tainan, Taiwan
Geetha Balakrishnan and Martin Lees both gave invited talks at the International Workshop on Frustrated and Topology in Condensed Matter Physics held in Tainan, Taiwan from 13th to 16th February 2014. Prof. Lieh Jeng Chang, who completed his PhD in our Group in 1997, hosted the Conference and was a senior member of the Organizing Committee.
Geetha Balakrishnan has been awarded a grant of £490k to study topological insulators.
April 2013, NMUM Poster Prize
Neutron Muon User Meeting Poster Prize. Congratulations to Joel Barker who was awarded joint first prize for his poster at the NMUM 2013.