On the question of ferromagnetism in alkali metal thin films

TL;DR

This study uses density functional theory to investigate the magnetic properties of alkali metal thin films, finding ferromagnetism only in a specific case of cesium films, which contrasts with simpler models.

Contribution

It provides first-principles calculations of the magnetic states of K and Cs thin films, highlighting differences from jellium model predictions.

Findings

Only 6-layer Cs film shows possible ferromagnetism.

Ferromagnetic and paramagnetic states are nearly degenerate in Cs films.

Results differ from predictions of the uniform jellium model.

Abstract

Electronic and magnetic structure of $(100)$ films of K and Cs are calculated within the plane-wave projector augmented wave (PAW) formalism of the density functional theory (DFT) using both local spin density approximation (LSDA) and the PW91 generalized gradient approximation (GGA). Only a 6 layer Cs film is found to have a ferromagnetic (FM) state which is degenerate with a paramagnetic (PM) state within the accuracy of these calculations. This is at variance with the results obtained from a finite thickness uniform jellium model (UJM). Implications of these results for the experiments on transition metal doped alkali metal thin films and bulk hosts are discussed.