Electromigration effects on atomic migration barriers in hard magnetic L1_0 intermetallic phases
We are investigating electromigration effects on the formation of hard magnetic intermetallic L10 phases. From an atomistic perspective this addresses the influence of external electric fields and currents on atomic migration in these binary ferromagnetic phases. We are especial-ly interested in the transition from the disordered A1 phase to the ordered L10 phase of FeNi, a promising candidate for a rare-earth-free high-performance hard magnetic material. The aims are an assessment in how far electromigration effects can be effective in processing hard mag-netic materials, as well as a better understanding of electromigration in intermetallic phases. Hence we extend the scope to the hard magnetic L10 phases of FePt, MnAl and MnGa. These four binary alloys cover a wide range of thermal ordering time scales and related experimental feasibilities.
In the first part we examine the effect of an external electric field on migration barriers of atoms near surfaces in the considered L10 phases. Using density functional theory (DFT) and surface-slab models for various surface configurations we study hops of atoms in the vi-cinity of the crystal surface and present the barrier change as a function of the applied field.
The second part concerns atomic migration under the influence of an electric current, i.e., the change in migration barriers as a result of so called electron wind forces. With DFT, unlike calculations of migration barriers in an external electric field, calculations of current-induced forces are not straightforward. Based on linear response theory we present a formal-ism to calculate corrections to atomic migration barriers in terms of ground state quantities accessible by DFT calculations.
The investigations are part of a joint project ‘Processing magnetic materials enhanced by electric fields or currents’ in the DFG SPP 1959 ‘Fields Matter’.