Ab initio prediction of magnetically dead layers in freestanding $\gamma$-Ce(111)

TL;DR

This study uses ab initio methods to show that the (111) surfaces of magnetic $ ext{γ}$-Ce are nonmagnetic, forming $ ext{α}$-like dead layers, and highlights how nanoscale effects and substrates can alter surface magnetism.

Contribution

It predicts that magnetic $ ext{γ}$-Ce surfaces form nonmagnetic dead layers, contrasting with $ ext{α}$-Ce, and demonstrates the influence of substrates on surface magnetic properties.

Findings

$ ext{γ}$-Ce(111) surfaces are nonmagnetic and $ ext{α}$-like.

Nanoscale effects can reverse bulk magnetic properties.

Substrate mismatch can suppress surface magnetic moments.

Abstract

It is well known that the surface of nonmagnetic $\alpha$-Ce is magnetically ordered, i.e., $\gamma$-like. One then might conjecture, in agreement with previous theoretical predictions, that the $\gamma$-Ce may also exhibit at its surfaces even more strongly enhanced $\gamma$-like magnetic ordering. Nonetheless, our result shows that the (111)-surfaces of magnetic $\gamma$-Ce are neither spin nor orbitally polarized, i.e., $\alpha$-like. Therefore, we predict, in contrast to the nonmagnetic $\alpha$-phase which tends to produce magnetically ordered $\gamma$-like thin layers at its free surfaces, the magnetic $\gamma$-phase has a tendency to form $\alpha$-like dead layers. This study, which explains the suppressed (promoted) surface magnetic moments of $\gamma$-Ce ($\alpha$-Ce), shows that how nanoscale can reverse physical properties by going from bulk to the surface in isostructural $\alpha$- and $\gamma$-phases of cerium. We predict using our freestanding surface results that a typical unreactive and non-diffusive substrate can dramatically influence the magnetic surface of cerium thin films in contrast to most of the uncorrelated thin films and strongly correlated transition metals. Our result implies that magnetic surface moments of $\alpha$-Ce(111) can be suddenly disappeared by increasing lattice mismatch at the interface of a typical unreactive and non-diffusive substrate with cerium overlayers.