Study On The Magnetic Properties Of Mn-doped Ge/Si Based Diluted Magnetic Semconductor Films

In our contemporary information industry,data processing is based on using of the charges of carriers,while information storage technique is based on using of spins of carriers. The use of carriers' charge and spin appears promising for a new series of device.Much of attention to diluted magnetic semiconductor(DMS) materials is due to its potential application in what is now called "spintronics" devices,which exploit spin in magnetic materials and charge in conventional semiconductors.Thanks to the incorporation of transition metal or rare earths magnetic ions,DMS exhibits some original properties as compared with conventional semiconductors.In my paper,we prepared series of nano-sized Mn_xGe_1-x and Mn_xSi_1-x samples by magnetron sputtering with high content of Mn.For Mn_xGe_1-x samples,one series were deposited directly,the others were deposited under substrate heating,while the Mn_xSi_1-x samples were only one series,which was deposited directly.X-ray diffraction(XRD) measurements suggest that our samples show intrinsic Ge or Si structure respectively.AFM measurements show that all films have uniform particle size distribution,and columnar growth pattern.Moreover,particle size increases clearly after substrate heating.However,all films do not show clear magnetic domain structure by magnetic force microscope(MFM), which suggest that there are not any high ferromagnetic clusters in our samples.From X-ray photoelectron spectroscopy(XPS) analysis,Ge is in the zero charge state with 28.21 eV binding energy and Mn is in the +2 or +3 state in Mn_xGe_1-x samples,and binding energies of both Mn and Si ions decrease because of the Mn-Si interactions in Mn_xSi_1-x samples. Electrical transport properties show that the resistivity increased with increasing temperature, showing obviously original semiconductor property of intrinsic Si or Ge.Hall effect measurements suggest that all films are p-type semiconductors without abnormal Hall effect at room temperature and concentration of carriers increase with the amount of Mn.Magnetic property measurements performed using a Physical Property Measurement System(PPMS) showed that directly deposited Mn_xGe_1-x samples show ferromagnetism at low temperature, while those deposited upon substrate heating were ferromagnetic at room temperature.Their ferromagnetism were intrinsic,induced by hole carriers through s,p-d exchange coupling between the weakly localized s,p hole carriers and the strongly localized d electron of the Mn atoms as well as by spin-orbital coupling of the hole carriers.All Mn_xSi_1-x samples show intrinsic ferromagnetism at 300 K,there is clearly a decrease in the saturated magnetization with an increase in the Mn ion concentration,which is contrary with that of hole carrier concentration.The ferromagnetism was induced by long-range ferromagnetic coupling between conduction electrons and the sparsely distributed Mn atoms.