Influence of pH on the structural optical and magnetic properties of Zn_1-xMn_xO thin films grown by sol-gel method

In this research, Zn_1-xMn_xO (0 ≤ x ≤ 0.2) thin films were synthesized by sol-gel technique for ferromagnetic and paramagnetic responses at high and low temperatures. In this respect, the produced films were characterized through X-ray diffraction (XRD), scanning electron microscope (SEM), UV-vis spectrometer and superconducting quantum interference device (SQUID) magnetometer. Based on the characterizations and measurements, the influence of pH on the structural, optical and magnetic properties of a Zn_1-xMn_xO thin films was scrutinized in detail. The analyzed results indicate that the films possess a good crystal quality and homogeneous, smooth surfaces with a pure hexagonal zincsite syn structure of ZnO without any Mn based phases. By increasing the Mn content, the films exhibited increase or decrease in both the c-axis lattice constant and fundamental band gap energy depending on their respective pH. It is clear that the Zn_1-xMn_xO (x = 0.02 and 0.05) thin films prepared at pH of 4.6 exhibited both a ferromagnetic at high temperatures (100, 200, and 300 K) and a paramagnetic response at low temperature (5 K), whilst Zn_1-xMn_xO (0.01 ≤ x ≤ 0.2) films prepared at pH value of 7.56 have paramagnetic behavior and antiferromagnetic contributions. The observed room temperature ferromagnetic behavior of the Zn_1-xMn_xO (x = 0.02 and 0.05) thin films at pH of 4.6 may be related to the interaction between Mn doping and the oxygen vacancies, an oxygen-vacancy-stabilized metastable phase Mn _2-xZn_xO_3-d or clustering of Mn ions.