Research On Preparation, Structures And Magnetic Properties Of Co-doped ZnO Diluted Magnetic Semiconductor Nano Materials

The discovery of giant magnetoresistance make magnetroelectronics the hot topics in theresearch on the magnetics. Along with the rapid decrease of the size, the properties of thesemiconductor devices will be influenced by the quantum effects. Diluted magnetic semiconductorcan obtain the ferromagnetism at room temperature by doping magnetic atoms into semiconductor.But the results after the magnetic doping are different, and even contradict, so the origin offerromagnetism in ZnO is still in debate. There are questions that whether the room temperatureferromagnetism can be obtained in semiconductor or not and how to get and control efficiently theferromagnetism with room temperature spin polarization in semiconductor, which had been confusedus about diluted magnetic semiconductor for a long time. In this paper, we fabricated Co-doped ZnOnanomaterials by hydrothermal and microemulsion methods to reveal the origin of ferromagnetism inZnO. Our researches make some benefit results, which might be widely uesd in the semiconductorindustry in future.The pure ZnO and Co-doped ZnO nanorods were prepared at low temperature by hydrothermalmethod with Zn(NO3)2·6H2O and Co(NO3)2·6H2O. The samples were characterized by energydispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), X-ray powderdiffraction (XRD) and physical property measurement system (PPMS). Good crystallization has beenconfirmed before and after doping and the crystal grows along the direction of the c axis. The averagediameters of pure ZnO and ZnO nanorods doped with2%Co are100nm, while the average lengthsare200nm. When the content of Co is above2%, the average diameter is10nm and the length50nm.Co doping significantly affects the growth of ZnO nanorods. In a series of ZnO nanorods withdifferent concentration of Co fabricated by hydrothermal method, pure ZnO is mainly diamagnetic,while other samples are mainly paramagnetic. Along with the increase of the concentration of Co, thesaturation magnetization of ferromagnetic part in ZnO samples changes little, and that theparamagnetism of the samples increases. The results of the study show that doped Co in ZnO samplesis not the origin of the ferromagnetism.The ferromagnetism in ZnO might be from the defects on Zn and O sites, and differentfabrication can induce different concentration of defects in ZnO with, so in this paper we fabricatedZnO by different method. The pure and Co-doped nano ZnO were prepared at low temperature bymicroemulsion with Zn(NO3)2·6H2O and Co(CH3COO)2·6H2O. Pure ZnO and Zn0.995Co0.005O samples are mainly diamagnetic, while the others are mainly paramagnetic. When Co content exceeds2%,samples’ paramagnetism increased significantly. When Co content increases from0to1%,ferromagnetism increase quickly; when Co content further increase to2%, ferromagnetism drasticallyreduce; when Co content continue to increase, ferromagnetism keeps unchanged. We also fabricated2%Cu doped ZnO by microemulsion, and found that the ferromagnetism in Zn0.98Cu0.02O andZn0.98Co0.02O are nearly the same. Since Cu is nonmagnetic and Co is magnetic, the result suggeststhat Co is not the origin of the ferromagnetism in ZnO. We performed the PL measurements on threeZn1-xCoxO (x=0,1%, and2%) samples. There are a large numbers of O vacancies in the pure ZnOsample. The stronger peak in Zn0.99Co0.01O indicates the higher concentration of O vacancies.However, the peak almost vanished in Zn0.98Co0.02O, indicating the suppressed concentration of Ovacancies.The concentration of O vacancies shows the consistent change with the ferromagnetism inZnO, which suggest that the ferromagnetism is caused by the O vacancies.In this paper, we proved that the ferromagnetism in ZnO-basedsemiconductor is from intrinsicdefects, and fabricated ZnO nano materials with changes ferromagnetism. The control of spin of theelectronics might be used in the produce of semiconductor industry.