Berlin 2015 – scientific programme

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MA: Fachverband Magnetismus

MA 46: Magnetic Thin Films I

MA 46.5: Talk

Thursday, March 19, 2015, 16:00–16:15, H 1012

Increased magnetic moment induced by lattice expansion from α-Fe to α^′-Fe₈N — Imants Dirba¹, Philipp Komissinskiy¹, Dominik Gölden¹, Oliver Gutfleisch^1,2, and •Lambert Alff¹ — ¹Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt — ²Fraunhofer-Projektgruppe für Wertstoffkreisläufe und Ressourcenstrategie IWKS, 63457 Hanau

We have grown buffer-free and epitaxial α-Fe and α^′-Fe₈N_x thin films by RF magnetron sputtering and molecular beam epitaxy onto MgO (100) substrates. The film thicknesses and densities have been determined with high accuracy by evaluating the Kiessig fringes of X-ray reflectometry measurements allowing a precise volume estimation. A gradual increase of the nitrogen content in the plasma led to an expansion of the iron bcc unit cell along the [001] direction resulting finally in a tetragonal distortion of about 10% corresponding to the formation of α^′-Fe₈N. The α-Fe lattice expansion was accompanied by an increase in magnetic moment to 2.61±0.06 µ_B per Fe atom, and an increase in anisotropy of around 6000 Oe. Our experiments show that - without requiring any additional ordering of the nitrogen atoms - the lattice expansion of α-Fe itself is the origin of the increased magnetic moment in α^′-Fe₈N.