Helen Walker
Instrument scientist
Email address:
Helen is a senior scientist with the ISIS Excitations Group, co-responsible for the Maps spectrometer, working on the development of barocalorics for green energy applications, and fundamental magnetism.
Introduction
I am an inelastic neutron scattering scientist, taking advantage of how neutrons interact with matter to investigate the dynamics and structure of functional materials. I also have considerable previous experience of working with X-rays; after spending several years working at synchrotrons in France and Germany.
My particular interests have evolved from exploring the magnetic properties of f-electron systems and transition metal oxides, particularly multiferroics and 5d systems, and more recently hybrid organic-inorganic materials such as Metal-Organic Frameworks (MOFs); to investigating lattice dynamics in technologically relevant materials. This resulted in being co-PI on an EPSRC grant to study phonons under pressure in barocaloric MOFs using neutrons in collaboration with Dr Anthony Phillips at QMUL (2019-2022). We examined a range of barocalorics using various neutron scattering techniques: nPDF, QENS and INS, with the aim of understanding what drives the large entropy change required for barocaloric cooling applications.
Teaching and Supervision
I currently supervise PhD student Peter Dung Nguyen-Minh with Anthony. Previously I supervised: Bernet Meijer (PhD 2023), and Richard Dixey (PDRA 2019-2023).
I was the co-chair of the ISIS Brazil neutron scattering school in September 2024, and was the course co-ordinator for the ISIS Neutron Training Course 2014-2022, which runs annually for 35 participants to get hands on experience of using ISIS instruments. I have also lectured on neutron scattering at the Institute for Materials Discovery at University College London, the Nanotechnology Centre at the Gdansk University of Technology and the SISN Advanced School on Magnetism in Ispra, Italy.
Conference organisation
Co-chair of Solid Materials for Sustainable Cooling—Caloric Effects and Devices Symposium at MRS Spring 2025 in Seattle WA (7-11 April)
Co-chair of Neutron scattering enabled energy materials design at MRS Spring 2023 in San Francisco CA (10-14 April 2023)
Selected recent publications
- Strong interlayer magnetic exchange coupling in La3Ni2O7−δ revealed by inelastic neutron scattering Sci. Bull. 69, 3221 (2024)
- Uncovering the phonon spectra and lattice dynamics of plastically deformable InSe van der Waals crystals, Nat. Comm. 15, 6248 (2024)
- Structure, spin correlations and magnetism of the S = 1/2 square-lattice antiferromagnet Sr2CuTe1-xWxO6 (0 ≤ x ≤ 1), Chem. Mater. 36, 501 (2024)
- On (not) deriving the entropy of barocaloric phase transitions from crystallography and neutron spectroscopy, J. Phys. Energy. 6, 011001 (2023)
- Dynamics in the ordered and disordered phases of barocaloric adamantine, Phys. Chem. Chem. Phys. 25, 9282 (2023)
- Origin of the large entropy change in the molecular caloric and ferroelectric ammonium sulfate, Adv. Func. Mat. 32, 2207717 (2022)
- Pressure dependence of rotational dynamics in barocaloric ammonium sulfate, Phys. Rev. B 106, 064302 (2022)
- Chapter 5: Inelastic neutron scattering under pressure, De Gruyter, 139-158 (2022)
- Viewpoint: Topological magnetism turns elementary, Physics 15, 30 (2022)
- Low thermal conductivity in a modular inorganic material with bonding anisotropy and mismatch, Science 373, 1017 (2021)
- Order by disorder from bond-dependent exchange and intensity signature of nodal quasiparticles in a honeycomb cobaltate, Nature Comm. 12, 3936 (2021)
- Antiferromagnetic double perovskite Ba2MnTeO6, Chem. Mater. 32, 7070 (2020)
- Exchange interactions mediated by non-magnetic cations in double perovskites, Phys. Rev. Lett. 124, 077202 (2020)
- NaYbS2, a new planar spin-1/2 triangular lattice magnet and possible spin liquid, Phys. Rev. B 98, 220409 (2018)
- Anomalous metamagnetism in the low carrier density Kondo lattice YbRh3Si7, Phys. Rev. X 8, 041047 (2018)
- Magnetic excitations in non-collinear antiferromagnetic Weyl semimetal Mn3Sn, Npj Quant. Mat. 3, 63 (2018)
- Fractionalized excitations in the partially magnetized spin liquid candidate YbMgGaO4, Nat. Commun. 9, 4138 (2018)
- Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by d10–d0 cation mixing, Nat. Commun.9, 1085 (2018)
- Coloumb spin liquid in anion-disordered pyrochlore Tb2Hf2O7, Nat. Commun. 8, 892 (2017)
- Magnetic structure and spin wave excitations in the multiferroic magnetic metal-organic framework (CD3)2ND2[Mn(DCO2)3], Phys. Rev. B 96, 094423 (2017)
- Resonant x-ray spectroscopy of uranium intermetallics at the U M4,5 edges, Phys. Rev. B 95, 245103 (2017)
- Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate, Nature 540, 559 (2016)
- Spin wave excitations in the tetragonal double perovskite Sr2CuWO6, Phys. Rev. B 94, 064411 (2016)
- Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7, Phys. Rev. Lett. 113, 147206 (2014)
- Robustness of basal-plane antiferromagnetic order and the Jeff=1/2 state to structural distortions in single-layer spin-orbit Mott insulators, Phys. Rev. Lett. 110, 117207 (2013)
- Negative thermal expansion and antiferromagnetism in the actinide oxypnictide NpFeAsO, Phys. Rev. B 85, 174506 (2012)
- Role of intrinsic disorder in the structural phase transition of magnetoelectric EuTiO3, Phys. Rev. B 85, 184107 (2012)
- Femtoscale magnetically induced lattice distortions in multiferroic TbMnO3, Science 333, 1273 (2011)
- Resonant X-ray Scattering Study of the URu2Si2 Hidden-order Phase, Phys. Rev. B 83, 193102 (2011)
- Circularly Polarized X-Rays as a Probe of Noncollinear Magnetic Order in Multiferroic TbMnO3 Phys. Rev. Lett. 102, 237205 (2009)
