Creating a bipolarity of semiconductors has been a key technology to develop recent advanced semiconductor devices. Such bipolarity for manganese oxides, of which “hole-doped manganites” exhibit a rich variety of electric transport and magnetic properties, has been of great importance. Although theoretical calculation predicts the presence of ferromagnetic “electron-doped manganites” with doping tetravalent cations [Q. Zhang and W. Zhang, Phys. Rev. B 68, 134449 (2003)], the ferromagnetic origin in experiments has been controversial due to the lack of direct experimental evidence. Here, we investigate the ferromagnetism in $\left(\text{La},\text{Ce}\right){\text{MnO}}_3$ thin films by measuring the magnetic circular dichroism in soft x-ray absorption (XMCD). Despite the presence of ${\text{Mn}}^{2+}$, i.e., electron doping for manganese, the ${\text{Mn}}^{2+}$ amount did not correlate with the Curie temperature, indicating the minor magnetic contribution of ${\text{Mn}}^{2+}$. More crucially XMCD measurements clarified that the ferromagnetism is not caused by the presence of ${\text{Mn}}^{2+}$ but by self-hole doping for manganese.

• Received 28 May 2008

DOI:https://doi.org/10.1103/PhysRevB.79.132405