Imants Dirba

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

Buffer-free and epitaxial α-Fe and α′-Fe8Nx 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 ± 0.06μB 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.

Engineering perpendicular magnetic anisotropy in Fe via interstitial nitrogenation: N choose K

In this work, combining experimental results and first principles calculations, we show that interstitial nitrogen not only serves for inducing tetragonality in α′-Fe8Nx but is also essential for achieving a high degree of perpendicular magneto-crystalline anisotropy, K. Our results demonstrate that the orbital magnetic moments of the iron atoms above and below N in the direction of magnetization are much more susceptible to the applied magnetic field than their in-plane counterparts, leading to a giant value of K as compared to a hypothetical distorted material without N.

Increased magnetic moment induced by lattice expansion from α-Fe to α-Fe 8 N

Here we provide experimental evidence by the careful preparation of thin films with controlled nitrogen content and induced tetragonality as a consequence. We have correlated the increase of the unit cell volume in expanded bcc Fe buffer-free and epitaxial thin films with their accurately measured magnetic moment, in-plane saturation field, magnetic domain patterns and change in electronic structure by systematically changing the amount of added nitrogen, allowing a comparison to the theoretical predictions.