Synthesis And Properties Of Ordered Porous CeO₂ Thin Films By Magnetron Sputtering

Cerium oxide?CeO₂?is one of the most attractive materials in rare-earth-oxide family for its multi-functionality in various fields,such as spintronic devices,buffer layers in oxide heterostructures,catalysis.In this paper,we deposited porous CeO₂ thin films by DC-reactive magnetron sputtering on porous anodic alumina substrates in a home-made system.Morphology of the films was implemented by using a field-emission scanning electron microscope?FE-SEM,Hitachi S-4800?.The crystallographic structure was examined using X-ray diffractometer?XRD?with Cu K radiation at a scan rate of 1°/min and 2?scanning from 20°to 80°.The composition of the porous CeO₂ thin films with porous anodic alumina?PAA?substrate was analyzed by EDS.Magnetic measurements were carried out using a physical property measurement system?PPMS-6700?at room-temperature.Current-voltage?I-V?characteristics of the devices were investigated using a Keithley 2612A source meter semiconductor characterization system with a DC voltage sweeping mode.The research results were listed as follows:?1?Ordered porous CeO₂ thin films were prepared on the ordered porous anodic alumina template?PAA?substrate by reactive DC magnetron sputtering.The relationship between the morphology and composition of CeO₂ thin films and the preparation conditions was studied.The structure and composition of the samples were characterized by XRD,SEM and EDS,and the best conditions for preparing ordered porous CeO₂ films were found.It was found that with the increase of sputtering time,the pore size of CeO₂ films became smaller and larger.?2?The physical properties of the prepared CeO₂ films were characterized by PPMS and other methods.The porous CeO₂ film has obvious room temperature ferromagnetism,and the external magnetic field perpendicular to the direction of the film surface is greater than the magnetic direction parallel to the film surface,the direction perpendicular to the film surface of the maximum saturation magnetization can reach 45 emu/cm³;the results show that CeO₂thin films have magnetic anisotropy,and the direction of easy magnetization was along the direction of the hole.Through experimental and theoretical analysis,it is found that the source of room temperature ferromagnetism of porous CeO₂ films is not only related to the porous structure of oxides,but also to the density of single electron oxygen vacancies.It is found that the exchange coupling between the single electron oxygen vacancies with local magnetic moments is similar to the exchange coupling between magnetic transition metals Fe,Co and Ni.?3?On the basis of the CeO₂/PAA composite film,the Ag/CeO₂/PAA/Al resistor switch device was prepared,and the control effect of the electric field on its resistance and magnetic change was studied.Through the characterization of the I-V characteristics of the Ag/CeO₂/PAA/Al device,it is found that the device realizes the stable function of the bipolar resistor switch.It is found that if the device is triggered to a high impedance state or low resistance state,the magnetic properties of the films will change accordingly,that is,under the action of the external electric field,the magnetic regulation of the CeO₂/PAA composite films can be realized by the resistance conversion behavior.It is considered that the characteristics of the bipolar resistor switch are related to the formation and fracture of the oxygen vacancy conductive filaments in the system.The research shows that in Ag/CeO₂/PAA/Al devices,the phenomenon of resistance and magnetic variation can be controlled at the same time under the action of electric field.The above research results enable porous CeO₂ thin films to be widely applied in multifunctional data storage and spintronic devices.