Is room temperature ferromagnetism possible in K-doped SnO2?

TL;DR

This study experimentally investigates K-doped SnO2 to assess room temperature ferromagnetism, finding phase separation and limited magnetic moments, contrasting with theoretical predictions of strong ferromagnetism.

Contribution

It provides the first experimental analysis of K-doped SnO2, revealing phase instability and weak magnetism, challenging prior ab-initio predictions.

Findings

K-doped SnO2 is thermodynamically unstable with phase separation.

K: SnO2 exhibits weak magnetic moments (~0.2 μB/K ion).

No long-range ferromagnetic order was observed.

Abstract

Ab initio studies have theoretically predicted room temperature ferromagnetism in crystalline SnO2, ZrO2 and TiO2 doped with non magnetic element from the 1A column as K and Na. Our purpose is to address experimentally the possibility of magnetism in both Sn1-xKxO2 and Sn1-xCaxO2 compounds. The samples have been prepared using equilibrium methods of standard solid state route. Our study has shown that both Sn1-xCaxO2 and Sn1-xKxO2 structure is thermodynamically unstable and leads to a phase separation, as shown by X-ray diffraction and detailed micro-structural analyses with high resolution transmission electron microscopy (TEM). In particular, the crystalline SnO2 grains are surrounded by K-based amorphous phase. In contrast to Ca: SnO2 samples we have obtained a magnetic phase in K: SnO2 ones, but no long range ferromagnetic order. The K: SnO2 samples exhibit a moments of the order of 0.2 {\mu}B/K /ion, in contrast to ab-initio calculations which predict 3{\mu}B, where K atoms are on the Sn crystallographic site. The apparent contradictions between our experiments and first principle studies are discussed.