A Theoretical Study of the Magnetic Structure of Bulk Iron with Radiation Defects
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A Theoretical Study of the Magnetic Structure of Bulk Iron with Radiation Defects Yang Wang1, D.M.C. Nicholson2, G.M. Stocks2, Aurelian Rusanu2, Markus Eisenbach2, and R. E. Stoller2 1 Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A. 2 Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A. ABSTRACT A fundamental understanding of the radiation damage effects in solids is of great importance in assisting the development of improved materials with ultra-high strength, toughness, and radiation resistance for nuclear energy applications. In this presentation, we show our recent theoretical investigation on the magnetic structure evolution of bulk iron in the region surrounding the radiation defects. We applied the locally self-consistent multiple scattering method (LSMS), a linear scaling ab-initio method based on density functional theory with local spin density approximation, to the study of the magnetic structure in a low energy cascade in a 10,000-atom sample for a series of time steps for the evolution of the defects. The primary damage state and the evolution of all defects in the sample were simulated using molecular dynamics with empirical, embedded-atom inter-atomic potentials. We also discuss the importance of thermal effect on the magnetic structure evolution. INTRODUCTION The radiation damage can have significant impact on the mechanical performance, the phase stability, and the lifetime of structural materials for fission and fusion reactors1. For example, the displacement defects produced in metals by intensive neutron flux can migrate and aggregate to form large clusters of defects and consequently alter the microstructure of the material and lead to the degradation of its mechanical properties. In particular, the defects can form energy barriers to the dislocation motion under the applied stress, causing the irradiation embrittlement, and thus result in the partial loss of plasticity that leads to the brittle fracture. Therefore, a fundamental understanding of the radiation damage effects in solids is of great importance in assisting the development of improved materials with ultra-high strength, toughness, and radiation resistance for nuclear energy applications. For the theoretical studies of radiation induced damages in Fe-based structural materials, while many research efforts have been devoted to the energetics calculation and molecular dynamics simulation of the formation and evolution of the interstitial defects and vacancies, little attention has been paid so far to the role of magnetism played in the defect dynamics. As shown by other studies2, the defects introduced in pure iron have exceptional properties. Specifically, the migration temperature of the interstitials in iron is much higher, and the vacancy cluster formation rate is much lower than in other transition metals. This can be attributed to the fact that iron has more unpaired 3d electrons than other transition metals, e.g., nickel and copper, and consequently, the energy increase due to th
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