顺磁性La_(2/3)Sr_(1/3)MnO_3层对Bi_(0.8)Ba_(0.2)FeO_3薄膜多铁性能的影响

Influence of paramagnetic La_(2/3)Sr_(1/3)MnO_3 layer on the multiferroic property of Bi_(0.8)Ba_(0.2)FeO_3 film

界面效应在提升异质结构材料的多铁性能方面有着重要的作用.本文采用脉冲激光沉积技术在SrTiO_3(STO)基片上制备了Bi_(0.8)Ba_(0.2)FeO_3(BBFO)/La_(2/3)Sr_(1/3)MnO_3(LSMO)异质结.X-射线衍射图谱表明异质结呈现单相外延生长,利用高分辨透射电镜进一步证实了BBFO为四方相结构.X-射线光电子能谱证实异质结中只存在Fe^(3+)离子,没有产生价态的变化,揭示了异质结铁电和铁磁性的增强与BBFO/LSMO的界面有关.同时,测试了磁电阻(MR)和磁介电(MD),当磁场强度为0.8 T,温度为70 K时,MR约为-42.2%,M D约为21.2%.并且发现在180 K时出现磁相的转变.实验结果揭示出异质界面效应在提升材料的多铁性和磁电耦合效应方面具有超常的优点,是加快多铁材料实际应用的有效途径.

Multiferroics simultaneously exhibit several order parameters such as ferroelectricity and antiferromagnetism,representing an appealing class of multifunctional material.As the only multiferroics above room temperature,BiFeO3（BFO） becomes an attractive choice for a wide variety of applications in the areas of sensors and spintronic devices.The coexistence of several order parameters brings about novel physical phenomena,for example,the magnetoelectric coupling effect.It allows the reversal of ferroelectric polarization by a magnetic field or the control of magnetic order parameter by an electric field.Heterostructure interface plays an important role in enhancing the ferroelectric and magnetic properties of multiferroic materials.Furthermore,the magnetoelectric coupling at the interface between the antiferromagnetism BFO and a ferromagnetic film has the close relation with achieving a functional multiferroic-ferromagnetic heterostructure.In order to determine the relationship between the multiferroic property and the interface experimentally,we prepare the Bi（0.8）Ba（0.2）FeO3（BBFO）/La（2/3）Sr（1/3）MnO3（LSMO） heterostructure on an SrTiO3（STO） substrate by pulsed laser deposition,and the structure characteristics and ferroelectric and magnetic properties are investigated.X-ray diffraction analysis shows that BBFO and LSMO films are epitaxially grown as single-phase.The further study by high-resolution transmission electron microscopy determines that the BBFO film has a tetragonal structure.The ferroelectric and magnetic measurements show that the magnetic and the ferroelectric properties are simultaneously improved,and the maximum values of the remnant polarization（2Pr） and the saturation magnetization of the heterostructure at room temperature are about 3.25 μC/cm2 and 112 emu/cm3,respectively.The reasons for enhancing the ferroelectric and ferromagnetic properties of heterostructure are demonstrated by X-ray photoelectron spectrum that shows being unrelated to the valence states of Fe element.On the contrary,interface effect plays a major role.In addition,the magnetic resistivities and dielectric properties of BBFO/LSMO heterostructure are investigated at temperatures in a range of 50 K to 300 K,finding that magnetoresistance（MR） and magnetodielectric（MD） are respectively about -42.2% and 21.9% at 70 K with a magnetic field of 0.8 T,and the transition of magnetic phase takes place near 180 K.Furthermore,the temperature dependences of magnetodielectric and magnetoloss（ML） present opposite tendencies,suggesting that magnetodielectric is caused by Maxwell-Wagner effect and the magnetoresistance.Experimental results reveal that heterogeneous interface effect shows the exceptional advantages in enhancing multiferroic property and magnetoelectric coupling effect of complex heterostructure material.It is an effective way to speed up the application of multiferroic materials.