Synthesis and properties of Zn(Cu–Mn)O dilute magnetic semiconductor thin films by chemical spray pyrolysis technique

• This work describes the synthesis of Zn1−2xCuxMnxO thin films with x = 0.05 at much lower ≤300 °C temperatures using the spray pyrolysis of the aqueous precursor solution.
• X-ray diffraction studies show absence of binary oxide phases and substitutional doping of Mn and Cu in ZnO.
• The binding energy shifts and structure of the Mn2p and Cu2p XPS lines confirm Mn and Cu substitute at Zn sites in the Zn0.90Cu0.05Mn0.05O films formed by spray pyrolysis process.
• The observed red shift of the optical band gap and the increased lattice parameter confirms Mn and Cu substitute at Zn sites.
• The distinct S-shaped magnetization hysteresis observed in Zn0.90Cu0.05Mn0.05O films clearly shows ferromagnetic ordering.

The Mn–Cu co-doped ZnO thin films with Zn1–2xCuxMnxO (x = 0.05) composition were synthesized by precursor solution spray pyrolysis at ≤300 °C in the highly crystalline c-axis oriented wurtzite structural form. X-ray diffraction studies show absence of binary oxide phases and substitutional doping of Mn and Cu in ZnO. The chemical environment of the dopant ions probed by the XPS analysis of the binding energy shifts and structure of the Cu and Mn XPS peaks show that Mn2+ and Cu2+ occupy Zn2+ sites in the ZnO lattice with Mn ions having bonding with lattice and interstitial O2− ions. The lowering of the optical band gap energy from undoped ZnO films at ∼3.22 eV to 3.16 eV shows doping by Mn and Cu in ZnO gives rise to band gap bowing in Zn0.90Cu0.05Mn0.05O thin films. The magnetization studies of the Zn0.90Cu0.05Mn0.05O films analyzed at 2 K and 300 K using squid magnetometer show ferromagnetic behavior with magnetization value of 5 × 10−5 emu and saturation magnetization at ∼15 kOe at 300 K. The observance of the ferromagnetism at room temperature is attributed to the mixed valence state of Mn in ZnO akin to the Mn3O4 spinel phase and the interstitial oxygen defects.