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Increased magnetic moment induced by lattice expansion from α-Fe to α' -Fe8N

: Dirba, I.; Komissinskiy, P.; Gutfleisch, O.; Alff, L.


Journal of applied physics 117 (2015), Nr.17, Art. 173911
ISSN: 0021-8979
ISSN: 1089-7550
Fraunhofer ISC ()
Fraunhofer IWKS ()

Buffer-free and epitaxial α-Fe and α' -Fe8N x thin films have been grown by RF magnetron sputtering onto MgO (100) substrates. The film thicknesses were 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 ± 0.06μ B per Fe atom and a considerable increase in anisotropy. These 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.