电荷、自旋、晶格强关联的铁磁合金薄膜/PMN-PT多铁性异质结中的磁电耦合效应

In this project, we are going to epitaxially grow FeRh1-xPdx alloy thin films with rich physics and room-temperature “ferromagnetic-antiferromagnetic” phase transition on PMN-PT single-crystal substrates in order to construct “charge, spin, and lattice strongly correlated ferromagnetic alloy film/PMN-PT crystal” multiferroic heterostructures。Through controlling the concentration of the Pd atom, ferromagnetic state, antiferromagnetic state or the “ferromagnetic-antiferromagnetic” phase transition will be achieved at room temperature for the FeRh1-xPdx films. By precisely controlling the film thickness, we will apply electric fields across the PMN-PT to modulate the lattice strain and charge carrier concentration of the films in order to realize strong magnetoelectric coupling effect through the electric-field-controllable and reversible “ferromagnetic-antiferromagnetic” phase transition at room temperature. By taking advantage of the electric field, magnetic field, and temperature field, we will study the mutual coupling rules among the spin, charge, and lattice degrees of freedom of the FeRh1-xPdx films so that we can deeply understand the effects of electric-field-induced lattice strain and interfacial charge on the electrical transport, magnetic, structural, carrier concentration, and magnetoelectric properties. We will try to obtain the intrinsic relationships among the lattice strain, structure, and physical properties, and the relationship between the carrier concentration and physical properties of the films, and disclose the underlying microscopic mechanisms that are responsible for the magnetoelectric coupling, thereby providing experimental basis and theoretical guidance for the possible device applications in microwave filter etc..

本项目提出将具有丰富物理效应且在室温下具有“铁磁－反铁磁”相变的FeRh1-xPdx合金薄膜外延生长在PMN-PT铁电单晶衬底上，构建“电荷、自旋、晶格强关联的铁磁合金薄膜/PMN-PT单晶”多铁性异质结。通过调控Pd原子掺杂浓度，使其在室温下分别处于铁磁态、反铁磁态以及“铁磁－反铁磁”相变附近，结合薄膜厚度的精确控制，对PMN-PT施加电场，调控薄膜的晶格应变和载流子浓度，在室温下实现电场可调控的“铁磁－反铁磁”可逆相变，从而获得强烈的磁电耦合效应。通过多场协同作用(电场、磁场、温度场)，研究薄膜的“电荷－自旋－晶格”自由度的相互耦合规律，深入理解电场诱导的晶格应变和界面电荷对薄膜的电输运、磁性、结构、载流子浓度以及磁电耦合性能的影响，分别获得“晶格应变－结构－性能”以及“载流子浓度－性能”之间的本征关系，揭示磁电耦合的微观物理机制，为其在滤波器等器件中的可能应用提供实验依据和理论指导。

本项目将拓扑绝缘体合金薄膜、锑化铋合金薄膜、锗锑合金薄膜以及稀磁半导体薄膜生长在Pb(Mg1/3Nb2/3)O3-PbTiO3（简称PMN-PT）铁电单晶衬底上，通过对PMN-PT单晶施加电场，诱导晶格应变和极化电荷，调控在其上生长的薄膜的晶格应变、载流子浓度、费米能级、电输运等性能，取得以下成果：（1）将Bi1.89Cr0.11Se3和Bi2-xCrxTe3 (x=0, 0.07, 0.14)拓扑绝缘体薄膜生长在PMN-PT铁电单晶衬底上，在室温下对PMN-PT施加电压，诱导极化电荷，实现了对拓扑绝缘体薄膜载流子浓度、载流子类型、费米能级、磁电导、电子相位相干长度、电子导电通道数等物性的非易失性调控，表明通过操控PMN-PT的极化电荷调控拓扑绝缘体的量子输运具有巨大优势；（2）将Bi1-xSbx (x=0, 0.07, 0.17)合金薄膜生长在PMN-PT铁电单晶上，通过电场调控PMN-PT的极化方向，以界面应变耦合为媒介实现了原位、非易失、可逆地调控薄膜的电学性能；（3）将GeTe合金薄膜生长在PMN-PT铁电单晶上，以界面应变耦合为媒介实现了薄膜的电学性能原位、非易失、可逆地调控，发现薄膜电阻在高、低电阻态之间切换300次后仍能保持稳定且仍能随着正、负电场的切换进行翻转；（4）通过对PMN-PT衬底施加电场，原位调控在其上外延生长的Cr:In2O3薄膜的载流子浓度，实现了对薄膜电阻、磁阻和费米能级的电场调控，并发现半导体薄膜/PMN-PT单晶异质结中电场诱导的极化电荷对薄膜性能的调控起主导作用，而晶格应变效应则可以忽略。. 项目执行期间共发表SCI检索学术论文14篇，其中包括npj Quantum Materials 1篇， Physical Review Materials 1篇，Physical Review Applied 1篇，ACS Applied Materials & Interfaces 4篇，Applied Physics Letters 2篇, Advanced Electronic Materials 1篇，《物理学报》综述论文2篇。授权中国发明专利1项。在本人指导下，有10位学生获得硕士学位（其中的7位学生是联合培养学生，在本课题组完成硕士学位论文工作，本人是毕业论文的共同指导导师），2位学生将于2020年6月获得博士学位。