Magnetic nanoscale laminates with tunable exchange coupling from first principles

Abstract

The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1-x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling

Magnetic MAX phases from theory and experiments; a review

“…This was later suggested to be related to the choice of competing phases, e.g., lack of the inverse perovskite Fe 3 AlC. By including these phases, Fe 2 AlC was found to be at best metastable, with ∆H cp = +116 meV/atom [7]. The first predicted stable magnetic MAX phase [7] to be synthesized was (Cr 1−x Mn x ) 2 AlC [12].…”

“…By including these phases, Fe 2 AlC was found to be at best metastable, with ∆H cp = +116 meV/atom [7]. The first predicted stable magnetic MAX phase [7] to be synthesized was (Cr 1−x Mn x ) 2 AlC [12]. Theoretically, a chemically ordered structure with Mn-C-Mn-Al-Cr-C-Cr-Al layer stacking along the c-direction was identified as the low energy structure, with FM ordered Mn layers coupled via nearly nonmagnetic Cr layers [7].…”

“…Phase stability calculations at 0 K have been proven successful when it comes to verify existing [12,14,22,26,81,[84][85][86] and, more importantly, predicting new MAX phases and related materials [3,7,25,87]. When it comes to magnetic MAX phases, almost all calculations to date neglect effects from temperature.…”

“…The first predicted stable magnetic MAX phase [7] to be synthesized was (Cr 1−x Mn x ) 2 AlC [12]. Theoretically, a chemically ordered structure with Mn-C-Mn-Al-Cr-C-Cr-Al layer stacking along the c-direction was identified as the low energy structure, with FM ordered Mn layers coupled via nearly nonmagnetic Cr layers [7]. The degree of intermixing between Cr and Mn layers was also addressed as a possible route to tune the sign and magnitude of the coupling.…”

“…[14,81]. In particular, the first magnetic MAX phases were predicted using DFT and evaluation of phase stability and subsequently synthesized [3,7,12,25]. The most successfull approach that has been used for evaluating the stability of a MAX phase of composition M n+1 AX n , defined as the formation enthalpy per atom ∆H(M n+1 AX n ), is to calculate the energy difference with respect to a set of competing phases,…”