Investigations on the effect of gaseous environment during synthesis on the magnetic properties of Mn-doped ZnO

The bulk polycrystalline samples of Mn-doped ZnO were synthesized with the nominal compositions Zn1-xMnxO (x = 0.02, 0.05, 0.10, 0.15, 0.20 and 0.25) via the standard solid state reaction route by sintering at 800 deg. C in air and argon atmospheres. The X-ray diffraction (XRD) studies of the as synthesized samples exhibit the presence of mainly wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples. In addition to this, XRD results also indicate the presence of secondary phases like ZnMn2O4 and Mn3O4 in minority. The M-H plots, recorded at room temperature, of the samples sintered in air reveals the presence of mainly paramagnetic behavior along with signature of weak ferromagnetic interactions. On the other hand, the M-H curves of all the samples sintered in argon atmosphere shows clear hysteresis loop indicating the presence of room temperature ferromagnetism (RTFM) in the samples. The value of magnetization at a particular field increases as content of Mn in the samples increases. The annealing of the samples in the hydrogenated argon further enhances the magnetization and ferromagnetism, whereas the same deteriorates on annealing in oxygen atmosphere. The possible mechanisms of the observed room temperature ferromagnetism have been discussed