A5061873708- Magnetic and transport properties of perovskites and related materials
- Magnetic properties of thin films
- Advanced Condensed Matter Physics
- Rare-earth and actinide compounds
- Physics of Superconductivity and Magnetism
- Theoretical and Computational Physics
- Magnetic Properties of Alloys
- Advanced Thermoelectric Materials and Devices
- Solid-state spectroscopy and crystallography
- High-pressure geophysics and materials
- Multiferroics and related materials
- Metallic Glasses and Amorphous Alloys
- Atomic and Subatomic Physics Research
- Inorganic Fluorides and Related Compounds
- Magnetic Properties and Applications
- Material Dynamics and Properties
- Hydrogen Storage and Materials
- Thermal Expansion and Ionic Conductivity
- Quantum and electron transport phenomena
- Spectroscopy and Quantum Chemical Studies
- Nuclear Materials and Properties
- Characterization and Applications of Magnetic Nanoparticles
- X-ray Diffraction in Crystallography
- ZnO doping and properties
- Surface and Thin Film Phenomena
Royal Holloway University of London
2010-2023
University of Liverpool
2000-2009
University of Castilla-La Mancha
2004
University of Oxford
1991-2000
Ricardo AEA (United Kingdom)
1992-1994
London Metropolitan University
1989
Research Complex at Harwell
1989
The defect structure of cubic fluorite structured yttria-stabilized zirconia $({\mathrm{ZrO}}_{2}{)}_{1\ensuremath{-}x}({\mathrm{Y}}_{2}{\mathrm{O}}_{3}{)}_{x}$ has been investigated over the composition range $0.100(4)<~x<~0.241(10)$ and temperatures $T(K)$ up to 2780(10) K, using single-crystal specimens. Analysis neutron x-ray diffraction data, including both Bragg coherent diffuse scattering components, identified three principal types defects within lattice. At low yttria concentrations...
We have determined the magnetic structures of single-crystal thin-films IrMn3 for crystallographic phases chemically-ordered L12 and chemically-disordered face-centred-cubic, which is phase typically chosen information-storage devices. For thin-film, we find same triangular structure as reported bulk material. determine face-centred-cubic alloy first time, differs from theoretical predictions, with moments tilted away crystal diagonals towards face-planes. study influence these two...
The suppression of transverse phonons by liquidlike diffusion in superionic conductors has been proposed as a means to dramatically reduce thermal conductivity thermoelectric materials [H. Lui et al. Nat. Mater. 11, 422 (2012)]. We have measured the ion transport and lattice dynamics original phonon-liquid electron-crystal ${\mathrm{Cu}}_{2}\mathrm{Se}$ using neutron spectroscopy. show that hopping time scales are too slow significantly affect vibrations persist at all temperatures....
A Reply to the Comment by L. Raymond, G. Albinet, and A.-M. S. Tremblay.Received 24 February 2006DOI:https://doi.org/10.1103/PhysRevLett.97.049702©2006 American Physical Society
High performance batteries based on the movement of Li ions in x CoO2 have made possible a revolution mobile electronic technology, from laptops to phones. However, scarcity and demand for energy storage renewables has led intense interest Na-ion batteries, including structurally-related Na CoO2. Here we determined diffusion mechanism Na0.8CoO2 using diffuse x-ray scattering, quasi-elastic neutron scattering ab-initio molecular dynamics simulations, find that sodium ordering provides...
We have investigated the quasi-one-dimensional Ni-chain compound <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>PbMn</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>Ni</a:mi><a:mn>6</a:mn></a:msub><a:msub><a:mi>Te</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>18</a:mn></a:msub></a:mrow></a:math> using theoretical DFT calculations, inelastic neutron scattering, and optical spectroscopy in order to understand nature of magnetic exchange...
The lowest-lying excited states in the S=1/2 one-dimensional Ising-like antiferromagnet ${\mathrm{CsCoCl}}_{3}$ consist of domain-wall (soliton) pair states. Although dynamical response function S(Q,\ensuremath{\omega}) has been calculated for these states, it not proved possible to explain results neutron scattering and Raman experiments without recourse introduction extra terms spin Hamiltonian. We argue against two modifications Hamiltonian proposed previous papers, a staggered field term...
The diffusion of hydride anions in LaSrCoO3H0.7 is measured for the first time. High-resolution quasielastic neutron scattering (QENS) data reveals onset mobility above 675 K, associated with hopping between vacant sites anion sublattice (see figure). temperature range at which takes place similar to used synthesis material, and loss hydrogen gas from sample. Supporting information this article available on WWW under http://www.wiley-vch.de/contents/jc_2089/2006/c1266_s.pdf or author. Please...
Specular reflectivity of neutrons and x rays can be used to determine the scattering length density profile a material perpendicular its surface. We have applied these techniques study amorphous, diamondlike, hydrocarbon films. By combination two we obtain not only mass density, but also concentration hydrogen, which varies in our case between 0 30 at. %. This method is new nondestructive way hydrogen within an error less than 2 % samples with sharp interfaces. It especially suited for...
A record 40% room temperature giant magnetoresistance has been achieved in a nanogranular $\mathrm{Co}∕\mathrm{Ag}$ alloy by optimizing the concentration, sputtering conditions, and cumulative short thermal treatments. Upon annealing, effect exhibits local minimum at $230\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ before reaching its maximum $300\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Assuming presence of both dipolar RKKY-like...
A powder sample of beta -PbF2 has been studied by neutron diffraction using the high resolution diffractometer at Rutherford-Appleton Laboratory. Rietveld profile refinements have performed on data collected roughly 100 temperatures from ambient to well above transition fast-ion phase, which occurs Tc approximately 710 K. The lattice parameter, a0(T), concentration Frenkel defects, and thermal parameters for both fluorine lead ions determined as a function temperature. Precise values a0(T)...
Spin correlations in the paramagnetic phase of La(2)CuO(4) have been studied using polarized neutron scattering, with two important results. First, temperature dependence characteristic energy scale fluctuations and amplitude structure factor are shown to be quantitative agreement predictions quantum nonlinear sigma model. Second, a comparison high-temperature series expansion equal-time spin diffuse intensity provides definitive experimental evidence for ring exchange.
Abstract Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order fractional excitations. Classical spin ices provide first context which it is possible control emergent magnetic monopoles, anisotropic exchange leads even richer behaviour associated with large quantum fluctuations. Whether ground state Yb 2 Ti O 7 a liquid or ferromagnetic phase induced by Higgs transition appears be...
The J1-J2 model on a square lattice exhibits rich variety of different forms magnetic order that depend sensitively the ratio exchange constants J2/J1. We use bulk magnetometry and polarized neutron scattering to determine J1 J2 unambiguously for two materials in new family vanadium phosphates, Pb2VO(PO4)2 SrZnVO(PO4)2, we find they have ferromagnetic J1. ordered moment collinear antiferromagnetic ground state is reduced, diffuse enhanced, as predicted bond-nematic region phase diagram approached.
The analysis of ac magnetic susceptibility data has shown that mechanically alloyed ${\mathrm{Fe}}_{30}{\mathrm{Ag}}_{40}{\mathrm{W}}_{30},$ a highly heterogeneous nanogranular system, exhibits critical dynamics in its transition to low-temperature spin-glass-like phase, as proved by the power-law divergence relaxation time at ${T}_{g}=19.7\mathrm{K},$ and dynamic scaling behavior out-of-phase component susceptibility. Both analyses yielded exponent...
The superparamagnetic blocking temperature of a series granular Co22Ag78 alloys grown by reactive sputtering under oxygen atmosphere exhibits minimum when plotted as function the pressure. magnetic stabilization observed above this is found to arise from exchange-bias between Co core and CoO shell, which appears be spin disordered. initial decrease in at low pressures mainly attributed inhibition RKKY-like interactions formation an insulating oxide layer, too thin give rise exchange bias,...
Exchange bias has been studied in epitaxial Fe/Ir0.2Mn0.8 (IrMn) bilayers grown by molecular beam epitaxy on MgO (0 0 1) substrates. The IrMn layer a chemically disordered fcc structure with an relationship of MgO(0 1)[1 1 0]//Fe(0 0]//IrMn(0 [1 0]. In this system, exchange is induced during growth at room temperature without post-annealing, applying small magnetic field, HA, along the bcc Fe 0] easy axis. dependence field and coercivity axis, measured up to approximately half Néel...
The sodium reordering in ${\text{Na}}_{x}{\text{CoO}}_{2}$ the vicinity of room temperature is rationalized at high $x$ terms phase transitions between square and striped phases. A striking hexagon-of-hexagons diffraction pattern observed for $x=0.78$ can be reproduced using coexisting phases that are related by simple shear deformations. All compositions exhibit a partial melting transition to disordered stripe just below temperature, which alters topology electrical conduction pathways.
The mineral linarite, ${\mathrm{PbCuSO}}_{4}(\mathrm{OH}{)}_{2}$, is a spin-$1/2$ chain with frustrating nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic exchange interactions. Our inelastic neutron scattering experiments performed above the saturation field establish that ratio between these exchanges such linarite extremely close to quantum critical point spin-multipolar phases state. We show predicted multipolar are fragile actually suppressed by tiny...
We report on combined neutron and resonant x-ray scattering results, identifying the nature of spin-orbital ground state magnetic excitations in ${\mathrm{LuVO}}_{3}$ as driven by orbital parameter. In particular, we distinguish between models based orbital-Peierls dimerization, taken a signature quantum effects orbitals, Jahn-Teller distortions, favor latter. order to solve this long-standing puzzle, polarized beams were employed prerequisite details structure, which allowed quantitative...
Fe/Mn is a model system in which to study exchange bias, since the antiferromagnetic (AF) Mn layers are believed have uncompensated moments with all spins aligned plane and parallel those of Fe. We determined microscopic AF ordering at interfaces using single-crystal neutron diffraction. An unexpected magnetic structure obtained, out-of-plane perpendicular This explains low bias field shows that simple assumed variety exchange-biased systems may well be revised.