Carrier Mediated Ferromagnetism above 300 K in ZnO:Mn

We will present evidence that Zn$_{1-x}$Mn$_{x}$O thin films, grown by reactive magnetron sputtering, are ferromagnetic at temperatures significantly above 300 K. The onset of the ferromagnetic behavior is sensitive to the exact growth conditions - in addition to the Mn concentration, the magnetic properties strongly depended on the substrate type, film growth temperature and Oxygen partial pressure. Anomalous~Hall Effect shows that the charge carriers are spin-polarized electrons, participating in the observed ferromagnetic behavior. Specifically, Zn$_{1-x}$Mn$_{x}$O on Al$_{2}$O$_{3}$(0001) substrates are single-phase, as characterized by XRD and TEM and the magnetic moment for a Mn concentration of x=0.03 is 4.8$\mu _{B}$/Mn at 350 K, one of highest moments yet reported for any Mn doped magnetic semiconductor. Growth of Zn$_{1-x}$Mn$_{x}$O films on Si/SiO$_{2}$ substrates leads to the formation of secondary phases and no ferromagnetism is observed in these cases.