Mechanical properties of CrN-based superlattices: Impact of magnetism

Superlattices represent an important design concept for materials with exceptional properties. In this work, we report on the influence of different interface orientations and magnetic configurations of CrN in B1 CrN/(TiN,AlN) superlattices on their mechanical and the structural properties studied with the help of density functional theory. The oscillations of interplanar spacings, formerly linked to the cleavage strength in similar material systems, were found to be in no correlation with the magnetic moments of individual CrN planes. An explicit consideration of the interfaces is important for an accurate estimation of elastic constants. In this context, the continuum mechanics-based Grimsditsch and Nizzoli method ignoring interface properties yields even qualitatively wrong results. Similarly, our calculations show that the ferromagnetic state of CrN as an approximation of (computationally much more demanding) paramagnetic magnetic state does not provide correct predictions of the material behaviour. In other words, explicit treatment of the magnetic moments as well as the interfaces is necessary for qualitatively correct modelling of CrN-based superlattices. Finally, the theoretically predicted elastic constants and fracture toughness values were corroborated by CrN/TiN micro-cantilever experiments.