Unraveling carrier’s kinetics in tuning the ferromagnetism of transparent Zn0.95Co0.05O epitaxial films

The search of transparent conducting and ferromagnetic properties in Zn1_xCoxO based diluted magnetic semiconductor is explored either by chemically alloying the different concentration (x) of Co or by n-type co-doping. The present work aims to explore the electrical conduction process at variable temperatures, in order to probe the room and low temperature ferromagnetism triggered in transparent Zn0.95Co0.05O films using inert xenon ion irradiation. The origin of the paramagnetism and the tunable ferromagnetism in transparent Zn0.95Co0.05O films is explained from different degree of concentric bound magnetic polarons (BMPs) stabilization inside variable range hopping spheres through implication of strongly and weakly bound carriers to O/Zn related lattice defects and tetrahedrally substituted Co2þ ions. The paramagnetic behavior in as deposited Zn0.95Co0.05O film arises from the smallest density of isolated concentric BMPs resulted mainly from marginal concentration of strongly localized carrier due to its highly insulating nature. The progressive enhancement in strongly localized carriers in post irradiated Zn0.95Co0.05O films as a function of fluence results in overlapping of static concentric BMPs to trigger onset of ferromagnetism. The strength of ferromagnetism is found to be maximal at a particular density of concentric BMPs optimized from the highest concentration of strongly localized carriers in insulating regime and substantial substituted Co2þ ions. Further enhancement in carrier concentration and reduction in substituted Co2þ ions is detrimental to ferromagnetism owing to non-static concentric BMPs percolation from the presence of weakly localized nature of carriers in intermediate regime.