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Diluted Magnetic Semiconductors（DMSs）are referred as a functional material,in which a small fraction of Transition Metal（TM）ions are substituted into host lattice of semiconductors.From the last few decades,DMSs have attracted a lot of interest due to their potential applications in the field of spin electronics（spintronics）,microelectronics,and optoelectronics.In order to utilize these devices,it is essential to develop DMS materials that display Room Temperature Ferromagnetism（RTFM）and lucid its mechanism.Since the prediction of high-temperature Ferromagnetism（FM）DMSs,TM-doped ZnO becomes one of the most extensive research topics of the DMS materials to achieve FM property at Room Temperature（RT）.However,the outcomes of RTFM were inconsistent,which led to controversy of observed mechanism of the FM behaviour in TM-doped ZnO based DMS.In this thesis,the magnetic property of Fe doped-ZnO,（Fe,Ni）co-doped ZnO,（Al,Fe）co-doped ZnO and（Cu,Fe）co-doped ZnO samples with a different concentration of dopant elements was studied.In addition,the high Pulsed Magnetic Field（PMF）was introduced during the process of hydrothermal technique.Characterization of doped ZnO samples was carried out using the X-ray diffraction（XRD）,Scanning Electron Microscopy（SEM）,Raman spectroscopy,X-ray Photoelectron Spectroscopy（XPS）,Ultra Violet spectra（UV）,Photoluminescence（PL）,and Vibrating Sample Magnetometer（VSM）.The main results are as follows:1.The Zn1-xFexO（x=0.01,0.02,0.03）,Zn1-xFexNi0.02O（x=0.01,0.02,0.03）,Zn1-xFe0.02AlxO（x=0.01,0.02,0.03,0.04）and Zn1-xFe0.02CuxO（x=0.01,0.02,0.03）were synthesized by hydrothermal method with high PMF.All the samples exhibited pure wurtzite structure and no secondary phases were detected within the sensitivity of the characterization measurements.It was found that Fe-doped ZnO,（Fe,Ni）co-doped ZnO and（Fe,Cu）co-doped ZnO systems show RTFM behavior for the low concentration of dopant ions.For the high concentration of dopant ions,the FM was suppressed and the paramagnetism was detected.However,In order to recognize the role of free carriers in mediating the ferromagnetic order,the A1 element（n-type dopant）was co-doped in the Fe-doped ZnO.The Fe and A1 ions were successfully incorporated into ZnO lattice and the RTFM was observed in co-doped ZnO.While,the RTFM behavior decreased with increasing the concentration of A1 ions.Therefore,this result showed that the free carrier-mediated exchange may not only able to stabilize the long-range ferromagnetic ordering.But,the VOs are responsible for the observed FM behavior.Hence,the A1 ions doped in ZnO:Fe matrix show better RTFM property as compare to other doping elements such as Ni,Cu.2.The influence of PMF on the microstructure,morphology,and RTFM of Fe doped ZnO,（Fe,Ni）,（Al,Fe）and（Cu,Fe）co-doped ZnO based DMSs were investigated systematically to understand and explain the possible mechanism of observed RTFM property.All the synthesized samples exhibited single phase hexagonal wurtzite structure.The Lorentz force affected the microstructure and morphology during the crystal growth.The results showed that the concentration of Oxygen Vacancies（VOs）and the content of TM ions in the host semiconductor were improved due to the PMF processing.The Optical analysis displayed that the absorption edge shifts to the higher wavelength（redshift）.The TM-doped ZnO poweders synthesized with HMF exhibited high Room Temperature Ferromagnetism（RTFM）.Hence,it is proposed that the inherent exchange interaction is mediated by magnetic ions through VO assist to produce Bound Magnetic Polorans（BMPs）,which is responsible for the observed RTFM in TM-doped ZnO DMS.From these experimental studies,it is determined that the origin of RTFM in ZnO based DMS materials are due to the intrinsic defect（such as oxygen vacancies）.In addition,the PMF assisted hydrothermal method is a potential way to improve the contents of intrinsic defects and RTFM of TM-doped ZnO materials.