  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.
