Vibrational and magnetic signatures of extended defects in Fe
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THE EUROPEAN PHYSICAL JOURNAL B
Regular Article
Vibrational and magnetic signatures of extended defects in Fe Robert Meyer 1,2 , Andreas Mutter 1,2 , Philipp Umst¨atter 1,2 , Volker Sch¨ unemann 1 , Tilmann Beck 3 , Marek Smaga 3 , and Herbert M. Urbassek 1,2,a 1 2
3
Physics Department, University Kaiserslautern, Erwin-Schr¨ odinger-Straße, 67663 Kaiserslautern, Germany Research Center OPTIMAS, University Kaiserslautern, Erwin-Schr¨ odinger-Straße, 67663 Kaiserslautern, Germany Department of Mechanical and Process Engineering, University Kaiserslautern, Erwin-Schr¨ odinger-Straße, 67663 Kaiserslautern, Germany Received 2 March 2020 / Received in final form 5 May 2020 Published online 22 June 2020 c The Author(s) 2020. This article is published with open access at Springerlink.com
Abstract. Defects change the phonon spectrum and also the magnetic properties of bcc-Fe. Using molecular dynamics simulation, the influence of defects – vacancies, dislocations, and grain boundaries – on the phonon spectra and magnetic properties of bcc-Fe is determined. It is found that the main influence of defects consists in a decrease of the amplitude of the longitudinal peak, PL , at around 37 meV. While the change in phonon spectra shows only little dependence on the defect type, the quantitative decrease of PL is proportional to the defect concentration. Local magnetic moments can be determined from the local atomic volumes. Again, the changes in the magnetic moments of a defective crystal are linear in the defect concentrations. In addition, the change of the phonon density of states and the magnetic moments under homogeneous uniaxial strain are investigated.
1 Introduction Since point defects are the most common defect type in metals, their influence on the phonon density of states (pDOS) was studied intensely. This influence is of basic importance because it enters the calculation of defect migration energies and defect formation entropies as well as the temperature dependence of the free energy of Fe. Early calculations of the vibrational spectra of vacancycontaining crystals were limited to pair potentials [1–5]. In view of the known limitations of pair potentials to describe the elastic properties of metals properly [6], later approaches turned to many-body potentials. Kislov and Mazurenko [7] calculated the vibrational spectrum of bccFe using the Finnis-Sinclair potential [8]. They found a shift of the transverse phonon peaks towards lower frequencies which they ascribed to a weakening of the interatomic interaction in the near-neighbor environment. Gairola et al. [9] calculated the local density of states of the neighbors of a vacancy in bcc Fe using a Green’s function method and a self-determined interaction potential. They found that changes in the vibrational spectrum are restricted to first neighbors; the pDOS features a decrease towards higher frequencies and a small shift towards lower frequencies. Self-interstitials show localized modes (related to the stretching of the dumbbell bond), which are absent for vaca
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