ABSTRACT
In this work, structural and magnetic characterizations of the Co doped
ZnO samples with different doping levels and preparation conditions were
made. The structural measurements have showed that all the doped samples
are found to be polycrystalline in nature with hexagonal wurtzite structure and
all the Co ion are incorporated in the ZnO wurtzite structure. In addition, the
structural analysis for the hydrogenated samples indicated the formation of
Oxygen vacancies.
The magnetic analysis has showed that the magnetic behaviour of the as
prepared Co doped ZnO samples is dominated by a paramagnetic component,
which is an indicative of uncoupled Co spins. However, the same samples
exhibited strong room temperature ferromagnetic behaviour (RTFM) when
they are hydrogenated which is attributed to the role of Oxygen vacancies in
accordance with the Bound Magnetic Polaron Model (BMP).
Furthermore, the analysis of the magnetisation reversal via fluctuation
fields for the hydrogenated samples shows that the distribution of activation
energies arises from both, the dispersion of anisotropy fields and the sizes
distribution of FM ordered regions. Due to the dispersion of anisotropy fields,
the medicated exchange coupling through vacancies at low ions
concentrations provide stronger RTFM behavior than the highly concentrated
ones. Accordingly, it believed that increasing the ions concentrations to
enhance the direct ions coupling may destabilize the polarons structure and
then weaken the irreversible magnetic behavior.