Theory of Curie temperature enhancement in electron-doped EuO

Abstract

We present a comparative, theoretical study of the doping dependence of the critical temperature TC of the ferromagnetic insulator-metal transitions in Gd-doped and O-deficient EuO, respectively. The strong TC enhancement in Eu1−xGdxO is due to Kondo-like spin fluctuations on the Gd sites, which are absent in EuO1−x. Moreover, we find that the TC saturation in Eu1−xGdxO for large x is due to a reduced activation of dopant electrons into the conduction band, in agreement with experiments, rather than antiferromagnetic long-range contributions of the RKKY interaction. The results shed light on possibilities for further increasing TC.