Effect Of High Pressure And Temperature Treatment On ZnO-based Semiconductors

In recent years,dilute ferromagnetic oxides and nitrides,which are wide-gap semiconductors with Curie temperatures Tc which is higher than room temperature, have become one of thepopular topic in the fields of spin-electronic semiconductors, material physics,condensed matter physics and so on.Diluted magnetic semiconductor(DMS) is a new kind of semiconducting materials combining the degree of freedom of the carrier's spin and charge.The research on DMS has become one of the hot topics.Solid-state reaction method is an important experiment measure.The preparation process was widely explored.We successfully synthesized ZnO nanoparticles doped with Mn and Co ions respectively by solid-state reaction method.The samples were processed under high pressure and temperature on a cubic high pressure apparatus. The structure and magnetic properties of our samples were analyzed and the origin of magnetic properties was discussed.The magnetization behaviors and the origin of ferromagnetism of Zn_1-xMn_xO samples were studied.The main points as follows:The structure properties,particle size of Zn_1-xMn_xO(x=0～0.06) samples,doped with different concentration and disposed at different high pressure,were characterized through X-ray diffraction(XRD) and transmission electron microscopy(TEM).The results of XRD test show that the Zn_1-xMn_xO sample has a single phase crystal structure.The magnetic properties of Zn_1-xMn_xO system were characterized by physical property measurement system(PPMS,Quantum Design).The relationship between magnetization,M,and magnetic field,H,under different doped concentrations and the M_H dependence under different high pressure of Zn_0.98Mn_0.02O were presented. The results showed that the saturated magnetization increased as the doped concentration increased.There was a competence between ferromagnetic and antiferromagnetic coupling in our samples.Meanwhile,high pressure had a significant effect on the ferromagnetic properties of our sample under room temperature.At the pressure of 3GPa,there was a significant improvement on the ferromagnetism of the sample.Based on the structure analysis and magnetic properties testing results,together with preparation process,we discussed the origin of magnetic behaviors in ZnO doped with transition metal ions.The XRD data of our samples showed that there was no secondary phase detected,so we ascribed the ferromagnetic order to be intrinsic. The magnetic property and origin of magnetism of the samples based on double exchange mechanism were discussed.The effect of high pressure and temperature on Zn_1-xCo_xO samples was investigated,and the results showed that high pressure and temperature treatment could produce a large grain and effectively decrease the varistor voltage.It can be a new method for preparing low varistor voltage ZnO ceramic varistor.Meanwhile,it is found that the nonlinear coefficient changed under the high pressure and temperature treatment.