Ferromagnetism in Mn-Doped ZnO: A Joint Theoretical and Experimental Study

We present a joint theoretical and experimental investigation on the origin of ferromagnetism in Mn-doped ZnO. Theoretical calculations revealed that the zinc vacancy (VZₙ) induces ferromagnetic ordering (FMO), whereas the oxygen vacancy (VO) quenches FMO in the Mn-doped ZnO system. This is further corroborated by the experimental results. Magnetic measurements revealed that Mn-doped ZnO shows room-temperature ferromagnetism (RTFM). Saturated magnetic moment per Mn²⁺ ion increases with oxygen partial pressure, indicating that the VZₙ enhances FMO in Mn-doped ZnO. Electron paramagnetic resonance and photoluminescence measurements revealed the presence of VZₙ in Mn-doped ZnO films. X-ray photoelectron spectroscopy measurements showed mixed oxidation states of Mn in Mn-doped ZnO films. Finally, we show that RTFM at very low doping concentrations is due to the overlapping of bound magnetic polarons. However, due to antiferromagnetic coupling at higher doping concentrations, the FMO weakens.