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- ItemMagnetic excitations in polyoxotungstate-supported lanthanoid single-molecule magnets: an inelastic neutron scattering and ab initio study(American Chemical Society, 2016-01-03) Vonci, M; Giansiracusa, MJ; Van den Heuvel, W; Gable, RW; Moubaraki, B; Murray, KS; Yu, DH; Mole, RA; Soncini, A; Boskovic, CInelastic neutron scattering (INS) has been used to investigate the crystal field (CF) magnetic excitations of the analogs of the most representative lanthanoid-polyoxometalate single-molecule magnet family: Na9[Ln(W5O18)2] (Ln = Nd, Tb, Ho, Er). Ab initio complete active space self-consistent field/restricted active space state interaction calculations, extended also to the Dy analog, show good agreement with the experimentally determined low-lying CF levels, with accuracy better in most cases than that reported for approaches based only on simultaneous fitting to CF models of magnetic or spectroscopic data for isostructural Ln families. In this work we demonstrate the power of a combined spectroscopic and computational approach. Inelastic neutron scattering has provided direct access to CF levels, which together with the magnetometry data, were employed to benchmark the ab initio results. The ab initio determined wave functions corresponding to the CF levels were in turn employed to assign the INS transitions allowed by selection rules and interpret the observed relative intensities of the INS peaks. Ultimately, we have been able to establish the relationship between the wave function composition of the CF split LnIII ground multiplets and the experimentally measured magnetic and spectroscopic properties for the various analogs of the Na9[Ln(W5O18)2] family. © 2016 American Chemical Society.
- ItemHot carrier transfer processes in nonstoichiometric titanium hydride(IOP Publishing, 2017-07-25) Wang, P; Iles, GN; Mole, RA; Yu, DH; Wen, X; Aguey-Zinsou, KF; Shrestha, SK; Conibeer, GThe absorber of the hot carrier solar cell (HCSC) needs to have a considerably reduced hot carrier thermalisation rate, in order to maintain the photo-generated hot carriers for enough time such that they can be extracted. The slow carrier cooling effect is predicted in materials in which the phononic band gap is sufficiently large to block the Klemens decay. Binary compounds with a large mass ratio between the constituent elements are likely to have large phononic band gap. Titanium hydride is one of these binary compounds that has the potential to become an absorber of the HCSC. Whilst a large phononic gap has been observed in stoichiometric TiH2, it has not been experimentally confirmed for hydrogen deficient TiH x (where x < 2). In this article, we report the phonon density of states of TiH1.65 measured using inelastic neutron scattering and presented to clearly show the phononic band gap. We also present the carrier thermalisation process of a TiH x (1< x <2) thin film by transient absorption, and estimate the carrier cooling time in this material. © 2017 The Japan Society of Applied Physics.
- ItemEvolution of the metallic state in LaNiO3/LaAlO3 superlattices measured by Li8β-detected NMR(American Physical Society (APS), 2021-11-12) Karner, VL; Chatzichristos, A; Cortie, DL; Fujimoto, D; Kiefl, RF; Levy, CDP; Li, RH; McFadden, RML; Morris, GD; Pearson, MR; Benckiser, E; Boris, AV; Cristiani, G; Logvenov, G; Keimer, B; MacFarlane, WAUsing ion-implanted Li8 β-detected NMR, we study the evolution of the correlated metallic state of LaNiO3 in a series of LaNiO3/LaAlO3 superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of 6.55T reveal two equal amplitude components: one with metallic (T linear) 1/T1 and a second with a more complex T dependence. The metallic character of the slow relaxing component is only weakly affected by the LaNiO3 thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing toward low T) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed in terms of electronic phase separation. ©2021 American Physical Society.
- ItemModulation of slow magnetic relaxation in Gd(III)‐tetrahalosemiquinonate complexes(Wiley, 2022-07-15) Dunstan, MA; Brown, DS; Sorace, L; Mole, RA; Boskovic, CIncorporating lanthanoid(III)‐radical magnetic exchange coupling is a possible route to improving the performance of lanthanoid (Ln) single‐molecule magnets (SMMs), molecular materials that exhibit slow relaxation and low temperature quantum tunnelling of the magnetization. Complexes of Gd(III) can conveniently be used as model systems to study the Ln‐radical exchange coupling, thanks to the absence of the orbital angular momentum that is present for many Ln(III) ions. Two new Gd(III)‐radical compounds of formula [Gd(18‐c‐6)X4SQ(NO3)].I3 (18‐c‐6=18‐crown‐6, X4SQ⋅−=tetrahalo‐1,2‐semiquinonate, 1: X=Cl, 2: X=Br) have been synthesized, and the presence of the dioxolene ligand in its semiquinonate form confirmed by X‐ray crystallography, UV‐Visible‐NIR spectroscopy and voltammetry. Static magnetometry and EPR spectroscopy indicate differences in the low temperature magnetic properties of the two compounds, with antiferromagnetic exchange coupling of JGd‐SQ∼−2.0 cm−1 (Hex=−2JGd‐SQ(SGdSSQ)) determined by data fitting. Interestingly, compound 1 exhibits slow magnetic relaxation in applied magnetic fields while 2 relaxes much faster, pointing to the major role of packing effects in modulating slow relaxation of the magnetization. © 2022 The Authors. Chemistry – An Asian Journal published by Wiley-VCH GmbH - Open Access - CC-BY-NC
- ItemA quantitative assessment of Geant4 for predicting the yield and distribution of positron-emitting fragments in ion beam therapy(IOP Publishing, 2024-06-21) Chacon, A; Rutherford, H; Hamato, A; Nitta, M; Nishikido, F; Iwao, Y; Tashima, H; Yoshida, E; Akamatsu, G; Takyu, S; Kang, HG; Franklin, DR; Parodi, K; Yamaya, T; Rosenfeld, AB; Guatelli, S; Safavi-Naeini, MObjective. To compare the accuracy with which different hadronic inelastic physics models across ten Geant4 Monte Carlo simulation toolkit versions can predict positron-emitting fragments produced along the beam path during carbon and oxygen ion therapy. Approach. Phantoms of polyethylene, gelatin, or poly(methyl methacrylate) were irradiated with monoenergetic carbon and oxygen ion beams. Post-irradiation, 4D PET images were acquired and parent 11C, 10C and 15O radionuclides contributions in each voxel were determined from the extracted time activity curves. Next, the experimental configurations were simulated in Geant4 Monte Carlo versions 10.0 to 11.1, with three different fragmentation models—binary ion cascade (BIC), quantum molecular dynamics (QMD) and the Liege intranuclear cascade (INCL++) - 30 model-version combinations. Total positron annihilation and parent isotope production yields predicted by each simulation were compared between simulations and experiments using normalised mean squared error and Pearson cross-correlation coefficient. Finally, we compared the depth of the maximum positron annihilation yield and the distal point at which the positron yield decreases to 50% of peak between each model and the experimental results. Main results. Performance varied considerably across versions and models, with no one version/model combination providing the best prediction of all positron-emitting fragments in all evaluated target materials and irradiation conditions. BIC in Geant4 10.2 provided the best overall agreement with experimental results in the largest number of test cases. QMD consistently provided the best estimates of both the depth of peak positron yield (10.4 and 10.6) and the distal 50%-of-peak point (10.2), while BIC also performed well and INCL generally performed the worst across most Geant4 versions. Significance. The best predictions of the spatial distribution of positron annihilations and positron-emitting fragment production along the beam path during carbon and oxygen ion therapy was obtained using Geant4 10.2.p03 with BIC or QMD. These version/model combinations are recommended for future heavy ion therapy research. © 2024 The Author(s). Published on behalf of Institute of Physics and Engineering in Medicine by IOP Publishing Ltd - Open Access - Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.