| Multiferroic material refers to a material containing two or more basic ferroics,which possess some couplings between them.Ferroics include ferroelectricity,ferromagneticity,ferroelasticity and ferrotoroidicity.Couplings exist between different ferroics,for example,materials with ferroelectric ity and ferromagneticity simultaneously can dispaly electric polarization by controlling magnetic field or dispaly magnetic polarization by controlling electric field,which is called magnetoelectric coupling effect.With the rapid development of the electronic information industry represented by large-scale integrated circuits,thin film materials are increasingly playing an important and critical role.Among thin film materials,composite magnetoelectric thin film are expected to be applied in new technology fields,such as information storage,filter and phase shifter,due to the magnetoelectric coupling effect.In fact,the key to achieve efficient magnetoelectric coupling in composite magnetoelectric thin film is to ensure that ferromagnetic phase in different directions can be applied different forces from ferroelectric phase.As a result,ferromagnetic phase is subjected to uneven forces.Thus,magnetic moment can be changed effectively by lattice distortion,which leades to a obvious changes of magnetic property in the ferromagnetic phase.Therefore,theoretical maximum magnetoelectric coupling effect can be obtained by preparing 1-3 type composite film.However,the preparation of 1-3 type film is very complex,which is not conducive to the practical application.0-0 type composite film can be obtained simply and directly by magnetron sputtering method.However,most of these films are of uniform two-phase distribution structure,namely,0-0 type which is hard to obtain efficient magnetoelectric coupling effect.If 0-0 type film can be prepared by magnetron sputtering method,and oriented growth is achieved in ferromagnetic phase at the same time,which means that ferromagnetic phase is subjected to the effect of anisotropic force field,it will be able to obtain highly efficient magnetoelectric coupling effect similar to that of 1-3 type film.Obviously,preparation and application of such composite film have important theoretical significance and practical value.To solve problems above,Cu doping BaTiO3(BTO)-Ni0.5Zn0.5Fe2O4(NZFO)thin films of 0-0 type are prepared by RF magnetron sputtering.Effects of preparation process and Cu2+ ion doping on crystal phase composition,orientation growth,lattice strain,magnetic property and dielectric property are studied.The specific research conclusions are as follows:(1)BTO-NZFO target and Cu target are simultaneously bombarded by RF magnetron sputtering,and Cu doping BTO-NZFO thin films with(222)plane orientation of NZFO are prepared by depositing on Si(111).(2)Cu2+ doping leads to anisotropic strain of NZFO lattice.Cu2+ ions replace Ni2+ ions of B sites in NZFO lattices.The oxygen octahedrons with Cu2+ ion center would be "elongated" because of Jahn-Teller effect of Cu2+ ions.As a result,interplanar spacing d//of NZFO(222)plane parallel to film surface stretches by 0.41%,and interplanar spacing d1 of NZFO(222)plane perpendicular to film surface shrinks by 0.62%.(3)Combined controlling of substrate induction and surface energy minimums leads to NZFO phase to grow along(222)plane.(4)A lot of Cu2+ ions replace Ni2+ ions in NZFO phase lattice,then magnetic moment at B position decreases sharply,thus A-B type exchange coupling becomes weaker,and thin films show weak magnetism.(5)Introduction of Cu2+ ions greatly improves permittivity of composite film. |
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