No room temperature ferromagnetism in Mn over-doped Zn1−xMnxO (x>0.02)

Mn-doped ZnO samples having composition Zn1−xMnxO (x=0.02, 0.04 and 0.05) were synthesized by solid state reaction technique with varying concentration of Mn from 0.02 to 0.05. Evidence of room temperature ferromagnetism was observed only in the composition Zn0.98Mn0.02O sintered at 500 °C. Our XRD pattern confirms the presence of Mn3O4 impurity phase in all the Zn1−xMnxO samples with the exception of Zn0.98Mn0.02O. We emphasize that the appearance of Mn3O4 phase in the system forbids the exchange type of interaction between the Mn ions and suppresses the ferromagnetism in all the Mn over-doped Zn1−xMnxO (x>0.02) system. SEM microstructure study also supports the interruption of exchange type of interaction inside the system with the increase in Mn concentration in the sample. Interestingly, for this particular composition, Zn0.98Mn0.02O sintered at 500 °C, glassy ferromagnetism type of transition is observed at low temperature. This type of transition is attributed to the formation of the oxides of Mn clusters at low temperature.

Research highlights▶ Zn1−xMnxO (x=0.02, 0.04 and 0.05) system synthesized by solid state reaction technique. ▶ Room temperature ferromagnetism in Zn0.98Mn0.02O. ▶ Glassy ferromagnetism at low temperature. ▶ Secondary phases of Mn3O4 suppresses the ferromagnetic ordering at low temperature.