Origin of ferromagnetism in Fe- and Cu-codoped ZnO

Abstract

Fe- and Cu-codoped ZnO was previously reported as a room-temperature dilute magnetic semiconductor. We have investigated the origin of the ferromagnetism in Zn0.95−xFe0.05CuxO using the zero-field Fe57 nuclear magnetic resonance and neutron diffraction. These measurements reveal that some Fe ions of Zn0.95−xFe0.05CuxO form a secondary phase, ZnFe2O4. Detailed comparison of nuclear magnetic resonance spectra of Zn0.95−xFe0.05CuxO, bulk ZnFe2O4 with normal spinel structure, and nanocrystalline ZnFe2O4 with inverted spinel structure shows that the secondary phase possesses an inverted spinel structure and is ferrimagnetic at room temperature, while normal zinc ferrite is nonmagnetic. The ferromagnetism in Fe- and Cu-codoped ZnO stems from the secondary phase, while the majority of Fe ions substituted into the ZnO lattice appears to remain magnetically inert.