Manipulating polar ferromagnetism in transition-metal-doped ZnO: Why manganese is different from cobalt (invited)

High-temperature magnetic ordering in $Mn2+$- and $Co2+$-doped ZnO diluted magnetic semiconductors has been predicted theoretically and confirmed experimentally to have different charge-carrier requirements. This paper summarizes some of these experimental and theoretical results and relates the different carrier polarity requirements for $300K$ ferromagnetism in $Mn2+:ZnO$ and $Co2+:ZnO$ to differences in the charge-transfer electronic structures of these two materials.