Possible room-temperature ferromagnetism in K-doped SnO2: X-ray diffraction and high-resolution transmission electron microscopy study
Résumé
Ab initio studies have theoretically predicted room-temperature ferromagnetism in crystalline SnO2, ZrO2, and TiO2 doped with nonmagnetic 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 microstructural analyses with high-resolution transmission electron microscopy. In particular, the crystalline SnO2 grains are surrounded by K-based 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 moment on the order of 0.2 μB/K /ion, in contrast to ab initio calculations which predict 3 μB, where K atoms are on the Sn crystallographic site. The apparent contradictions between our experiments and first-principles studies are discussed.