Search for ferromagnetism in transition-metal-doped piezoelectric ZnO

We present results of a computational study of ZnO in the presence of Co and Mn substitutional impurities. The goal of our work is to identify potential ferromagnetic ground states within the (Zn,Co)O or (Zn,Mn)O material systems that are also good candidates for piezoelectricity. We find that robust ferromagnetism is not obtained by substitution of Co or Mn on the Zn site, unless additional carriers (holes) are also incorporated. This is consistent with the conventional wisdom that carriers are required to induce ferromagnetism in diluted magnetic semiconductors, but in contrast to a previous theoretical prediction for this system [K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000); K. Sato and H. Katayama-Yoshida, Phys. Status Solidi B 229, 673 (2002)]. We propose a practical scheme for achieving such p-type doping in ZnO.