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The present paper describes Raman studies of chemically synthesized nanocrystalline cobalt-substituted (up to 10%) ZnO samples exhibiting room temperature ferromagnetism. These studies were carried out using Laser excitation wavelengths -457.9, 532 and 785 nm. The Raman spectra of the samples excited with 457.9 nm show predominantly lattice modes of ZnO because of pre-resonance enhancement. In the Raman spectra of cobalt added ZnO samples excited with 532 and 785 nm, clear evidence is seen for the presence of Co3O4 (an impurity phase not detectable in XRD) in the samples with cobalt exceeding 3%. The presence of Co3O4 in the samples having higher concentration of cobalt explains the nonmonotonic increase in magnetization with Co-concentration in the ZnO1 - xCox samples. [ABSTRACT FROM AUTHOR]

The present paper describes room temperature ferromagnetism in Ni-doped SnO2 thick films (∼3 µm) with a maximum saturation moment at a Ni-concentration of 8 at.%. On further increase in Ni-concentration, saturation magnetization decreases with the appearance of a paramagnetic component. Orthorhombic phase of SnO2, found along with the tetragonal phase in the undoped SnO2, disappears at 6 at.% of Ni in the film. The appearance of NiO beyond 5 at.% is responsible for the change in lattice constants and preferential orientation of the grains. The observed magnetic behavior is correlated with these phases/observations. [ABSTRACT FROM AUTHOR]