October 2017 - Welcome to 3 New Ph.D. Students
The Group welcomes 3 new Ph.D, students, Sam Holt, Bethany Hampshire, and Sam Curley. Sam Holt will be working with Geetha Balakrishnan on Skyrmionic materials. Beth will be working under the joint supervision of Don Paul (Warwick) and Aidy Hillier (ISIS-RAL) on the use of negative muons, studying at Warwick and at ISIS. Sam Curley will be working with Paul Goddard on an ERC project studying Quantum Materials under Extreme Conditions.
July - September 2017 URSS projects
Two Undergraduate Research Support Scheme (URSS) project students have joined the group over the summer. Oliver Rigby (3rd year Physics) is working with Martin Lees and Santosh Kumar on the physics of rare earth transition metal magnets as part of the PRETAMAG project. Stepan Marek (2nd year Physics) is working with Oleg Petrenko on SrRE2O4 frustrated magnetic materials.
July 2017 - Group Summer Meal
The Group held its summer meal at Seasons restaurant in Leamington Spa. The whole group took the chance to get together and to wish Saurabh Barua bon voyage, as he is leaving the Group soon when his post-doc comes to a close.
The meal came about due to the excellent organisation of Dan Brunt. Thanks Dan!
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.
Almost the whole group decamped to Abingdon to attend the annual Theoretical and Experimental Magnetism Meeting (TEMM 2017). The meeting was combined with IOP Magnetism TCM joint group symposium and the UK-Korea workshop on strongly correlated electron systems. It was a great chance to talk to old friends and colleagues and to make new contacts. Dan Brunt gave an invited talk at the TCM theory meeting.
Prof. Ray Osborn, who is based at Argonne National Laboratory in the USA visited us just before TEMM and gave a CMP seminar, while Dr. Sylvain Petit of LLB -CEA Saclay came back from Abingdon with us to visit our labs and discuss future projects.
Monica Hatnean Ciomaga and Geetha Balakrishnan both attended this year's APS March meeting in New Orleans. Part scientific meeting – part Mardi Gras!
January 2017 - Ph.D. for Joel Barker
Congratulations to Joel Barker on successfully defending his Ph.D. thesis. Joel, whose Ph.D. 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 Ph.D. 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.
October 2016, new Ph.D. students join the Group
Welcome to Amy Tedstone and Matt Pearce who have joined the Group as Ph.D. students. Amy will be working jointly with Rachel Edwards of the Ultrasound Group and Martin Lees and Geetha Balakrishnan on Permanent Magnet Systems (PRETAMAG project). Matt has joined Paul Goddard working on Low Dimensional and Molecular Magnets.
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.
Congratulations to Mo Saghir on successfully defending his Ph.D. thesis. Mo, whose Ph.D. work was supervised by Geetha Balakrishnan, has been working on growing new topological insulators and superconductors in both bulk and nano form.
Mo's thesis is entitled Topological Insulators: A Study of Bulk Crystalline and Nanomaterials and can be downloaded from his web page.
|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).