Helen
Walker
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​​​​​​​​Summary​


​I am 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.​







​​Measured and simulated spin wave excitations in the multiferroic magnetic metal-organic framework (CD3)2ND2[Mn(DCO2)3]
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​​​Research​

​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 evoved 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 entrropy change required for barocaloric cooling applications.

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​​​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)

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Selected recent publications​



Strong interlayer magnetic exchange coupling in La3Ni2O7−δ revealed by inelastic neutron scattering

Sci. Bull. ​​69, 3221​​​ (2024​​)



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Uncovering the phonon spectra and lattice dynamics of plastically deformable InSe van der Waals crystals

Nat. Comm. ​​15, 6248​​​ (2024​​)

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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​)

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Dynamics in the ordered and disordered phases of barocaloric adamantine

Phys. Chem. Chem. Phys. ​​25, 9282​ (2023)



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Origin of the large entropy change in the molecular caloric and ferroelectric ammonium sulfate​

Adv. Func. Mat. ​​32, 2207717​​​​​​ (2022​)

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​​ 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​)​



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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​)


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Order by disorder from bond-​dependent exchange and intensity signature of nodal quasiparticles in a honeycomb cobaltate​​​

Nature Comm. ​​12, 3936​​​​​ (2021​)


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Antiferromagnetic double perovskite Ba​2MnTeO6

Chem. Mater. ​​32, 7070​​​​​ (2020​)


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​Exchange interactions mediated by non-magnetic cations in double perovskites

Phys. Rev. Lett. ​​124, 077202​ (2020​)

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NaYbS2, a new planar spin-1/2 triangular lattice magnet and possible spin liquid
Phys. Rev. B 98, 220409 (2018)​

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Anomalous metamagnetism in the low carrier density Kondo lattice YbRh3Si7
Phys. Rev. X ​​8, 041047​ (2018)


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Magnetic excitations in non-collinear antiferromagnetic Weyl semimetal Mn3​Sn​ 
Npj Quant. Mat. ​​3, 63 (2018)


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​Fractionalized excitations in the partially magnetized spin liquid ​​candidate YbMgGaO4​​​
Nat. Commun. 9, 4138 (2018)


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Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by d10–d0 cation mixing ​​

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Coloumb spin liquid in anion-disordered pyrochlore Tb2Hf2​O7
Nat. Commun. 8, 892 (2017)

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Magnetic structure and spin wave excitations in the multiferroic magnetic metal-organic framework (CD3)2ND2[Mn(DCO2)3]​
Phys. Rev. B 96, 094423 (2017)​


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Resonant x-ray spectroscopy of uranium intermetallics at the U M4,5 edges
Phys. Rev. B 95, 245103 (2017)​

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Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate
Nature 540, 559 (2016)​


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Spin wave excitations in the tetragonal double perovskite Sr2CuWO6
Phys. Rev. B 94, 064411 (2016)


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Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7
Phys. Rev. Lett. 113, 147206 (2014)

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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)​

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Negative thermal expansion and antiferromagnetism in the actinide oxypnictide NpFeAsO
Phys. Rev. B 85, 174506 (2012)​


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Role of intrinsic disorder in the structural phase transition of magnetoelectric EuTiO3
Phys. Rev. B 85, 184107 (2012)​

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Femtoscale magnetically induced lattice distortions in multiferroic TbMnO3
Science 333, 1273 (2011)


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​Resonant X-ray Scattering Study of the URu2Si2 Hidden-order Phase
Phys. Rev. B 83, 193102 (2011)​



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​Circularly Polarized X-Rays as a Probe of Noncollinear Magnetic Order in Multiferroic TbMnO3

Phys. Rev. Lett. 102, 237205 (2009)​​
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