Mechanical alloying:: a route to room-temperature ferromagnetism in bulk Zn1-xMnxO

High-purity commercial ZnO and MnO2 powders have been used as starting materials for the production of the compound Zn0.98Mn0.02O. The magnetic properties of these source materials have been investigated before a powder-mix corresponding to Zn0.98Mn0.02O was mechanically alloyed for periods of up to 15 h. It is found that the effect of grinding the two powders together generates a ferromagnetic component that exhibits hysteresis at room temperature. At 290 K, the component has a coercivity of 110 +/- 10 Oe and saturates in a field of about 6 kOe. The magnetic moment per Mn atom is estimated to be about 0.1 mu(B). On low-temperature anneal, there is a slight increase in the saturation magnetisation of the compound until, after anneal at 700 degreesC, the ferromagnetism has decayed and, at room temperature, the powder-mix shows a nett paramagnetic behaviour. On a further anneal at temperatures up to 1000 degreesC, several low-temperature peaks are observed in low-field measurements. We interpret these as arising due to the thermal decay of the MnO2 and its subsequent interaction with ZnO. No room-temperature ferromagnetism is observed after anneal at 700 degreesC. (C) 2004 Elsevier B.V. All rights reserved.