Preparation And Performance Study Of Lead-free Magnetoelectric Composite Film

Multiferroic magnetoelectric?ME?materials not only simultaneously exhibit magnetic and ferroelectric properties,but also exhibit magnetoelectric coupling effect.Direct control of electric polarization?magnetization?via external magnetic?electric?field can be achieved based on the coupled ME effect.Multiferroic magnetoelectric materials have drawn increasing research interest due to the prospect of applications in the electronic information functional devices.ME composite materials typically yield a giant coupling response above room temperature,have drawn increasing research interest.Compared with bulk multiferroic composite,ME composite thin films have better compatibility with microelectronic devices and are beneficial to understand the physical mechanism of magnetoelectric effects at the atomic scale,so most researches on ME materials have focused mainly on the nanostructured thin films.The research of heterostructure ME composite films is still in the primary stage and the growth control of high-quality heterostructure ME composite films is still the key.It is still a difficult and hot point in the research of ME materials to prepare high quality heterostructure composite films.High-performance multiferroic magnetoelectric composite films are mainly composed of lead-based ME composites.Recently,the focus of ongoing research has been on lead-free ME composites,considering the environmental toxicity of lead.Although BaTiO₃?BTO?-based lead-free magnetoelectric composites have been studied for a long time,there are few studies on BT-based magnetoelectric composites with excellent electrical properties and magnetoelectric coupling properties.And BTO-based magnetoelectric composite thin films with excellent magnetoelectric coupling properties and high Curie temperature are rarely reported.In this paper,the doped BTO-based systems were used as the ferroelectric phase,and NiFe₂O₄?NFO?material was used as the ferromagnetic phase.The pulsed laser deposition method was used to grow high quality 2–2 type layered heterostructure magnetoelectric composite films,and an environment-friendly multi-ferroelectric composite film material was constructed.The main research work of this paper is as follows:1.The preferred BTO-based ferroelectric thin films with excellent properties were successfully prepared.Firstly,A and B sites of BTO were doped by Ca²⁺and Zr⁴⁺,respectively,The Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃?BCZT?lead-free ferroelectric thin films epitaxially grown on the?001?-SRO/STO substrates were prepared by PLD.The effects of laser energy,laser frequency and deposition temperature on the properties of BCZT films were studied systematically.BCZT films have excellent electrical properties,buttheCurietemperatureislower.Secondly,the0.8BaTiO₃-0.2Na_0.5Bi_0.5TiO₃?0.8BT–0.2NBT?and 0.65BaTiO₃-0.35Na_0.5Bi_0.5TiO₃?0.65BT–0.35NBT?ferroelectric thin films were prepared by combining Na_0.5Bi_0.5TiO₃?NBT?with BTO system.The two kinds of films showed excellent electrical properties and higher Curie temperature,especially the remanent polarization of 0.8BT–0.2NBT and 0.65BT–0.35NBT are P_r³2.4?C/cm² and P_r³8.1?C/cm²,respectively.The introduction of NBT phase is one of the important ways to improve the electrical properties and Curie temperature of BTO-based ferroelectric materials.2.The magnetoelectric properties of BTO-based magnetoelectric composite films were studied.The magnetoelectric effect of BTO-base layered composite film was calculated based on the mechanical parameter model,the optimum volume fraction ratio between the ferroelectric layer and the ferromagnetic layer is estimated,when the volume fraction of the ferromagnetic layer and the ferroelectric layer is approximately equal,the magnetoelectric performance is the best,it provides guidance for the construction of BTO-based magnetoelectric composite films.Then,the 2–2 type NFO/BCZT epitaxial heterostructure composite films were prepared by PLD.NFO/BCZT composite film has good ferroelectric,piezoelectric,ferromagnetic and excellent ME coupling properties(?_E⁹3 mV·cm^?1·Oe^?1),it provides an alternative for the design of new multiferroelectronic devices.3.The mechanism of improving the magnetoelectric properties and Curie temperature of BTO-based magnetoelectric composite films was studied.NFO/0.8BT–0.2NBT lead-free magnetoelectric composite films with high Curie temperature were prepared by PLD in?001?-STO single crystal substrate.The structure,morphology,dielectric,ferroelectric,piezoelectric,ferromagnetic and magnetoelectric coupling properties of NFO/BTO and NFO/0.8BT–0.2NBT magnetoelectric composite films were studied.The results show that:?1?The Curie temperature?T_c²32°C?of the NFO/BTO–NBT composite thin film is higher than that of NFO/BTO composite thin film?¹20°C?.The introduction of NBT possessing a larger T_c?³20°C?,can effectively improve the T_c of BTO-based ME composites.?2?The ferroelectric,piezoelectric and magnetoelectric coupling properties of the NFO/BTO–NBT thin film are higher than those of the NFO/BTO thin film.The introduction of NBT phase can improve the ferroelectric and piezoelectric properties of BTO ferroelectric phase,thus effectively improving the magnetoelectric coupling performance.4.The effect of deposition sequence on the magnetoelectric properties of BT-based layer magnetoelectric composite films was studied.The NFO/0.65BT–0.35NBT?the top layer is NFO?and 0.65BT–0.35NBT/NFO?the top layer is BT–NBT?bilayer thin films epitaxially grown on the?001?-SRO/STO substrates were prepared by PLD,the physical mechanism of the effect of different growth order of ferromagnetic phase and ferroelectric phase on magnetoelectric properties was analyzed..The results show that:?1?X-ray diffraction patterns indicated that all the films display the?00l?preferred orientation and epitaxial heterostructure.?2?NFO/0.65BT–0.35NBTand0.65BT–0.35NBT/NFO heteroepitaxial magnetoelectric composite films exhibit simultaneously excellent ferroelectric,dielectric,ferroelectric and ferromagnetic properties,especially excellent ferroelectric properties?P_r²7.3?C/cm²,P_r³1.8?C/cm²?.?2?NFO has different lattice distortion with different deposition sequences,the magnetic coercive field H_c of NFO/0.65BT–0.35NBT structure is significantly lower than that of 0.65BT–0.35NBT/NFO structure,indicating that the magnetic domain can be rotated easier in the NFO/0.65BT–0.35NBT.?3?The deposition sequences have a great influence on the ME coupling properties of the bilayer thin films,the magnetoelectric coupling of the NFO/0.65BT–0.35NBT heterostructure better than that of the 0.65BT–0.35NBT/NFO heterostructure,due to the different substrate clamping effect.