33 results found
Classical models of spin-lattice coupling are at present unable to accurately reproduce results for numerous properties of ferromagnetic materials, such as heat transport coefficients or the sudden collapse of the magnetic moment in hcp-Fe under pressure. This failure has been attributed to the absence of a proper treatment of effects that are inherently quantum mechanical in nature, notably spin-orbit coupling. This paper introduces a time-dependent, non-collinear tight binding model, complete with spin-orbit coupling and vector Stoner exchange terms, that is capable of simulating the Einstein-de Haas effect in a ferromagnetic Fe15 cluster. The tight binding model is used to investigate the adiabaticity timescales that determine the response of the orbital and spin angular momenta to a rotating, externally applied Β field, and we show that the qualitative behaviours of our simulations can be extrapolated to realistic timescales by use of the adiabatic theorem.
An analysis of the trends in the torque contributions with respect to the field strength demonstrates that SOC is necessary to observe a transfer of angular momentum from the electrons to the nuclei at experimentally realistic Β fields.
The simulations presented in this paper demonstrate the Einstein-de Haas effect from first principles using a Fe cluster.
Ma P-W, Mason DR, Van Boxel S, et al., 2023, Athermal evolution of nanocrystalline tungsten driven by irradiation, Journal of Nuclear Materials, Vol: 586, Pages: 154662-154662, ISSN: 0022-3115
Reali L, Gilbert MR, Boleininger M, et al., 2023, γ-photons and high-energy electrons produced by neutron irradiation in nuclear materials, Journal of Nuclear Materials, Vol: 585, ISSN: 0022-3115
Neutrons interacting with atomic nuclei in most of the materials included in the current fusion reactor designs—notably tungsten, ferritic and stainless steels, copper alloys—generate a γ-photon flux that is comparable in magnitude and energy with that of the neutrons, and which in turn generates an intense flux of high-energy electrons in the materials themselves. The occurrence of these γ- and electron fluxes has implications, among others, for the mobility of crystal defects in the materials, for the stability of the plasma, and for the internal heating of reactor components. While a highly spatially resolved numerical calculation of neutron, photon, and electron fluxes on the reactor scale is computationally unfeasible, it is possible to provide estimates based on solutions of Boltzmann's transport equation in a stationary and homogeneous material. Within their limits of validity, these estimates are robust and straightforward and they enable studying photon and electron generation in various materials, under different fission and fusion irradiation conditions and at various locations inside a reactor. We show that the irradiation environment provided by the IFMIF irradiation facility is similar to the expected fusion power plant conditions both in terms of the energy and intensity of photons and electrons generated by the neutrons in tungsten and steels.
Fedorov M, Wróbel JS, London AJ, et al., 2023, Precipitation of Cr-rich clusters in Fe-Cr alloys: Effects of irradiation from first principles modeling and experimental observations, Journal of Nuclear Materials, Pages: 154715-154715, ISSN: 0022-3115
Reali L, Gilbert MR, Boleininger M, et al., 2023, Intense <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>γ</mml:mi></mml:math>-Photon and High-Energy Electron Production by Neutron Irradiation: Effects of Nuclear Excitations on Reactor Materials, PRX Energy, Vol: 2
Warwick AR, Thomas R, Boleininger M, et al., 2023, Dislocation density transients and saturation in irradiated zirconium, International Journal of Plasticity, Vol: 164, Pages: 103590-103590, ISSN: 0749-6419
Boleininger M, Mason DR, Sand AE, et al., 2023, Microstructure of a heavily irradiated metal exposed to a spectrum of atomic recoils, Scientific Reports, Vol: 13
<jats:title>Abstract</jats:title><jats:p>At temperatures below the onset of vacancy migration, metals exposed to energetic ions develop dynamically fluctuating steady-state microstructures. Statistical properties of these microstructures in the asymptotic high exposure limit are not universal and vary depending on the energy and mass of the incident ions. We develop a model for the microstructure of an ion-irradiated metal under athermal conditions, where internal stress fluctuations dominate the kinetics of structural evolution. The balance between defect production and recombination depends sensitively not only on the total exposure to irradiation, defined by the fluence, but also on the energy of the incident particles. The model predicts the defect content in the high dose limit as an integral of the spectrum of primary knock-on atom energies, with the finding that low energy ions produce a significantly higher amount of damage than high energy ions at comparable levels of exposure to radiation.</jats:p>
Reali L, Boleininger M, Gilbert MR, et al., 2022, Macroscopic elastic stress and strain produced by irradiation, NUCLEAR FUSION, Vol: 62, ISSN: 0029-5515
Warwick AR, Boleininger M, Dudarev SL, 2021, Microstructural complexity and dimensional changes in heavily irradiated zirconium, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
Mason DR, Granberg F, Boleininger M, et al., 2021, Parameter-free quantitative simulation of high-dose microstructure and hydrogen retention in ion-irradiated tungsten, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
Ma P-W, Dudarev SL, 2021, Elastic dipole tensor of a defect at a finite temperature: Definition and properties, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
Gilbert MR, Arakawa K, Bergstrom Z, et al., 2021, Perspectives on multiscale modelling and experiments to accelerate materials development for fusion, JOURNAL OF NUCLEAR MATERIALS, Vol: 554, ISSN: 0022-3115
Duc N-M, Wrobel JS, Klimenkov M, et al., 2021, First-principles model for voids decorated by transmutation solutes: Short-range order effects and application to neutron irradiated tungsten, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
Wróbel JS, Zemła MR, Nguyen-Manh D, et al., 2021, Elastic dipole tensors and relaxation volumes of point defects in concentrated random magnetic Fe-Cr alloys, Computational Materials Science, Vol: 194, Pages: 110435-110435, ISSN: 0927-0256
Ma P-W, Dudarev SL, 2021, Nonuniversal structure of point defects in face-centered cubic metals, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
Mason DR, Das S, Derlet PM, et al., 2020, Observation of Transient and Asymptotic Driven Structural States of Tungsten Exposed to Radiation, PHYSICAL REVIEW LETTERS, Vol: 125, ISSN: 0031-9007
Ma P-W, Mason DR, Dudarev SL, 2020, Multiscale analysis of dislocation loops and voids in tungsten, PHYSICAL REVIEW MATERIALS, Vol: 4, ISSN: 2475-9953
Ma P-W, Dudarev SL, 2020, CALANIE: Anisotropic elastic correction to the total energy, to mitigate the effect of periodic boundary conditions, COMPUTER PHYSICS COMMUNICATIONS, Vol: 252, ISSN: 0010-4655
Arakawa K, Marinica M-C, Fitzgerald S, et al., 2020, Quantum de-trapping and transport of heavy defects in tungsten, NATURE MATERIALS, Vol: 19, Pages: 508-+, ISSN: 1476-1122
Mason DR, Duc N-M, Marinica M-C, et al., 2019, Relaxation volumes of microscopic and mesoscopic irradiation-induced defects in tungsten, JOURNAL OF APPLIED PHYSICS, Vol: 126, ISSN: 0021-8979
Dudarev SL, Liu P, Andersson DA, et al., 2019, Parametrization of LSDA plus U for noncollinear magnetic configurations: Multipolar magnetism in UO2, Physical Review Materials, Vol: 3, Pages: 1-14, ISSN: 2475-9953
To explore the formation of noncollinear magnetic configurations in materials with strongly correlated electrons, we derive a noncollinear LSDA+U model involving only one parameter U, as opposed to the difference between the Hubbard and Stoner parameters U−J. Computing U in the constrained random phase approximation, we investigate noncollinear magnetism of uranium dioxide UO2 and find that the spin-orbit coupling (SOC) stabilizes the 3k ordered magnetic ground state. The estimated SOC strength in UO2 is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3k magnetic ground state with canted ordering of uranium f orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the noncollinear 3k state, which has the lowest energy even in an undistorted lattice. The choice of parameter U in the LSDA+U model has a notable quantitative effect on the predicted properties of UO2, in particular on the magnetic exchange interaction and, perhaps trivially, on the band gap: The value of U=3.46eV computed fully ab initio delivers the band gap of 2.11 eV in good agreement with experiment, and a balanced account of other pertinent energy scales.
Mason DR, Sand AE, Dudarev SL, 2019, Atomistic-object kinetic Monte Carlo simulations of irradiation damage in tungsten, MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, Vol: 27, ISSN: 0965-0393
The Einstein-de Haas (EdH) effect, where the spin angular momentum of electrons is transferred to the mechanical angular momentum of atoms, was established experimentally in 1915. While a semiclassical explanation of the effect exists, modern electronic structure methods have not yet been applied to model the phenomenon. In this paper, we investigate its microscopic origins by means of a noncollinear tight-binding model of an O2 dimer, which includes the effects of spin-orbit coupling, coupling to an external magnetic field, and vector Stoner exchange. By varying an external magnetic field in the presence of spin-orbit coupling, a torque can be generated on the dimer, validating the presence of the EdH effect. The avoided energy level crossings and the rate of change of magnetic field determine the evolution of the spin. We also find that the torque exerted on the nuclei by the electrons in a time-varying B field is not only due to the EdH effect. The other contributions arise from field-induced changes in the electronic orbital angular momentum and from the direct action of the Faraday electric field associated with the time-varying magnetic field.
Ma P-W, Dudarev SL, 2019, Effect of stress on vacancy formation and migration in body-centered-cubic metals, Physical Review Materials, Vol: 3
Ma P-W, Dudarev SL, 2019, Symmetry-broken self-interstitial defects in chromium, molybdenum, and tungsten, Physical Review Materials, Vol: 3
Ma P-W, Dudarev SL, 2019, Universality of point defect structure in body-centered cubic metals, Physical Review Materials, Vol: 3
Dudarev SL, Mason DR, Tarleton E, et al., 2018, A multi-scale model for stresses, strains and swelling of reactor components under irradiation, NUCLEAR FUSION, Vol: 58, ISSN: 0029-5515
Coury MEA, Dudarev SL, Foulkes WMC, et al., 2018, Erratum: Hubbard-like Hamiltonians for interacting electrons in s, p, and d orbitals (vol 93, 075101, 2016), Physical Review B, Vol: 98, ISSN: 2469-9950
Nordlund K, Zinkle SJ, Sand AE, et al., 2018, Improving atomic displacement and replacement calculations with physically realistic damage models., Nature Communications, Vol: 9, Pages: 1-8, ISSN: 2041-1723
Atomic collision processes are fundamental to numerous advanced materials technologies such as electron microscopy, semiconductor processing and nuclear power generation. Extensive experimental and computer simulation studies over the past several decades provide the physical basis for understanding the atomic-scale processes occurring during primary displacement events. The current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model, has nowadays several well-known limitations. In particular, the number of radiation defects produced in energetic cascades in metals is only ~1/3 the NRT-dpa prediction, while the number of atoms involved in atomic mixing is about a factor of 30 larger than the dpa value. Here we propose two new complementary displacement production estimators (athermal recombination corrected dpa, arc-dpa) and atomic mixing (replacements per atom, rpa) functions that extend the NRT-dpa by providing more physically realistic descriptions of primary defect creation in materials and may become additional standard measures for radiation damage quantification.
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