三方四方相共存多铁性薄膜全电场调控的磁交换偏置效应研究

In this proposal, a novel full electrical field controlled magnetic exchange bias bilayer is suggested. This new kind of magnetic exchange bias bilayer is fabricated by doped BiFeO3(BFO) ferromagnetic (FM) film with co-exiting R3c and orthorhombic phases and antiferromagnetic (AFM) R3c BFO film. Researches are focused upon the mechanism of the ferromagnetism induced by the doped resulted chemical strains, as well as the mechanism of the external electrical field controlled exchange bias between the doped BiFeO3 FM layer and the AFM BiFeO3 layer. In detail, the polarization of the magnetic domains in BFO is controlled by external electric filed due to ME effect, thus, the FM or AFM coupling between doped BFO and BFO can be established and modulated by electric field. In this way, a novel full electric filed controlled exchange bias effect in BFO related homosturcture bilayer can be realized. We propose study the electric field controlled globe properties of the exchange bias effects and the local magnetic-, ferroelectric- domains, as well as the ME effects in the morophotropic phase boundary between the doped BOF and BOF homo-structure bilayer, including static and dynamic in multi-scale and multi-technologies integrated and cooperated. Based upon these studies, we will reveal the mechanism of the stain, due to the rotation of Fe-O octahedral structure in doped BFO and BFO, induced modulation of the full electric field controlled magnetic exchange bias, including exchange bias field, magnetic coercivity, training effects. The conclusion of the study will supply information for the design and fabrication of the magnetoelectric random access memories devices both in theoretical and technological.

提出制备全电场调控的以三方相/四方相共存掺杂BiFeO3铁磁层、三方相BiFeO3反铁磁层并具有磁交换偏置效应同质双层膜的新思想。研究掺杂应力诱导铁磁相的形成机理、电场诱导的铁电应力对铁磁相与反铁磁相界面磁交换偏置效应调控规律及其机理。具体地，通过外加电场调控三方相BiFeO3中铁电畴取向并通过磁电耦合来调控BiFeO3铁磁畴取向和形态来实现对掺杂BiFeO3铁磁性薄膜表面的局域磁矩进行调控，进而实现电场对铁磁层与反铁磁层之间磁交换偏置耦合效应调控。提出宏观磁交换偏置效应测量与准同型性相界处局域磁畴和铁电畴及其磁电耦合受电场应力调控进行静态和动态的多方法和多测度的同步协同测量新技术和新方法。研究应力导致的Fe-O八面体旋转取向对同质双层膜中磁电耦合机理、磁交换偏置场、铁磁层磁矫顽力和training效应的调控规律及其机理。为设计和制备出具有应用价值的磁电耦合随机存储器件提供理论和技术支持。

本项目的支持下，完成了一下几方面的工作：.1、.BiFeO3及其Ho，Gdp掺杂薄膜合成制备与多铁性研究：.完成了Bi1-xHoxFeO3(x=0.00，0.05，0.07，0.10，0.12，0.15)和Bi1-xGdxFeO3（x=0.00、0.05、0.07、0.10、0.12、0.15）研究取得了如下进展：。.对于Ho和Gd掺杂样品掺杂浓度在7-12%之间样品呈现R3C和证据相（Pnma）共存，当掺杂量为大于12-15%时，样品的结构转变为正交Pnma相。特别是在5-12%掺杂量样品中明显存在同型形相结构。在具有同型形相结构的样品中获得了最佳的多铁电性：最佳饱和磁矩为64.4emu/cm3，最佳剩余极化值Pr=30.97μC/cm2。比未掺杂时的BiFeO3样品约大一个数量级。 .随着掺杂浓度薄膜剩余极化强度值增大的原因：（1）Ho3+，Gd3+离子取代了易挥发的Bi3+离子，减弱了由氧空位聚集引起的对铁电畴的钉扎作用，从而提高剩余极化强度。（2）由于Ho3+，Gd3+的掺杂降低了样品的晶格结构对称性，增强了晶格畸变程度，提高BiFeO3薄膜的极化程度；（3）Ho3+，Gd3++离子掺杂增强了样品的磁性，样品中存在的磁电耦合效应，使Ho3+掺杂样品极化度增加。.对不同温度下热处理后得到的Bi0.88Ho0.12FeO3和Bi1-xGdxFeO3（x=0.00、0.05、0.07、0.10、0.12、0.15）样品铁电测量结果表明： .掺杂样品中，既存在BiFeO3结构的三方相，又有正交相的迹象。随着掺杂浓度的增大，正交相逐渐增加并分布在六方相的界面，在界面处产生较大的化学应力，因此5%~12%这个应力层为样品的准同型相界层。对不同温度下热处理后样品的磁性稍有不同。在7%~12%掺杂浓度中，样品的磁性稍强些，而且观察到自发交换偏置效应。.研究结果表明样品在出现同型形相界时其同时具有良好的铁磁性和铁电性，由此可推断出该温度下，准同型相界区域内可能存在较强的磁电耦合效应。.2、碱金属掺杂BiFeO3 纳米颗粒研究：.1）碱金属对A位掺杂BiFeO3样品的磁性影响：.研究表明：1、K掺杂能调控成样品品质。2、K+掺杂能调控BiFeO3相变温度温度。3、铁电/顺电热滞后效应减小。.K掺杂样品中的磁电耦合导致导致所合成的BiFeO3样品具有显著的磁交换偏置效应。综合表征