Preparation And Characterization Of Layered Magnetoelectric Composites

In 1960,Astrov discovered a single-phase magnetoelectric?ME?material named Cr₂O₃.After that,people found the ME effect in Ti₂O₃,GaFeO₃,the boron and the phosphate compound.However,the experimental results show that the single-phase ME materials have a very small ME conversion coefficient at the room temperature,which leads to them failing to be applied to the smart device.In order to obtain a desired ME conversion coefficient,many people are turning their attention to ME composite materials.In general,the ME composite materials can be divided into three types:0-3 type particulate composite,2-2 layered composite and 1-3 type columnar composite.In this paper,the 2-2 layered ME composite materials have been prepared by the electroless deposition and magnetron sputtering.The material properties are characterized by means of X ray diffraction?XRD?,energy dispersive spectroscopy?EDS?,scanning electron microscopy?SEM?,vibration sample magnetometer?VSM?,scratch tester and thermal ME integrated testing system.The main research contents are as follows:Firstly,according to the electroless deposition,the Ni/PZT/Ni,as a layered ME composite material,is fabricated by using metallic nickel and PZT-5H.In this scheme,the main salt is nickel sulfate hexahydrate and the reducing agent is hydrazine hydrate or sodium hypophosphite.In addition,we can change the reaction temperature,time and pH to optimize the test conditions.The present experiments show that?1?the purity of the nickel layer with hydrazine hydrate up to ninety percent is far higher than the one with Sodium hypophosphite;?2?the optimal pH value of sodium hypophosphite as reductant is between 10 and 11,and the bonding strength between prepared film and substrate is 30 mN;?3?when the magnetic field strength is between0KOe and 8KOe,with the increase of magnetic field,the electrode strength of the composite becomes small,and the maximum electric polarization is 0.547C/m².Secondly,based on the magnetron sputtering method,the Ni/PMN-PT,as a layered ME composite material,is prepared by means of nickel target and PMN-PT.By changing the substrate temperature,one can adjust the nickel film crystallization and control its bonding strength with PMN-PT.Through analyzing the apparent morphology,magnetic and mechanical properties of the material,it can be found that the nickel film is relatively uniform and the lattice direction is consistent with the direction of?1 1 1?.When the temperature varies from room temperature to 100?,the magnetic property of the film will become better and better,and the hardness of the film is the best at 100?.But the second critical load between the film at 100?and the substrate becomes the smallest value because of the high temperature.As a result,it can be concluded that the thermal stress has a significant effect on the adhesion of the film.In addition,the smallest value of the electrode strength is only0.05C/m².After taking overall consideration,the optimal experimental temperature is80?where the magnetism is 340emu/cc and the bonding force is 173mN.Thirdly,according to the magnetron sputtering method,the layered ME composite Ni/PMN-PT,which consists of nickel target and PMN-PT,is prepared by controlling sputtering pressure,argon flow rate,ignition pressure,sputtering power and sputtering time.By analyzing the present Ni/PMN-PT,one can find that the magnetization strength can reach 420emu/cc if the time of magnetization is 30minutes.Furthermore,the magnetization strength is 345emu/cc when the open glow pressure is 0.7Pa,and it increases to 300emu/cc when the rate of argon flow keeps 90sccm.Besides,when the sputtering power is 75W,the electric polarization is the strongest and it is 0.08C/m².