Ferromagnetism-to-paramagnetism transition in the ZnMnO system

The magnetic properties of Mn- and P-doped ZnO prepared by using the solid state reaction and pulsed laser deposition (PLD) were investigated by measuring the magnetization and the absorption derivative of the electron paramagnetic resonance (EPR). The film's thickness was about 0.3 mu m. The X-ray diffraction pattern indicated a single-phase polycrystalline ZnO structure without any MnO2 phase in both the polycrystalline samples and the thin films. The magnetic behaviors of the samples were determined by using an alternating gradient magnetometer (AGM) at room temperature. All the bulk samples showed ferromagnetism at room temperature. Mn-doped ZnO films with Zn3P2 added also showed ferromagnetism at room temperature. A transition from ferromagnetism to paramagnetism with increasing in sintering temperature was detected in the EPR experiments. The absorption derivative of the EPR signal showed hyperfine splitting for the samples sintered at 800 and 900 degrees C due to a spin degeneracy of Mn2+, the hyperfine splitting disappeared for the samples sintered at 1000 degrees C due to a superposition of the six lines of hyperfine splitting.