稀土正铁氧体中的磁弹耦合效应研究

Both piezomagnetization and magnetostriction are macroscopic manifestation of the magnetoelastic coupling effect. These interesting physical phenomena have potential applications in important areas of spin device, sonar and stress sensor, ultrasonic transducer and so on. This project will study the magnetoelastic coupling effect associated with the spin reorientation in RFeO3 system by means of magnetic measurements under hydrostatic pressure, strain testing under temperature/magnetic fields and neutron diffraction technique. By optimizing the composition of samples, the large piezomagnetic and magnetostrictive effects under low driving fields can be obtained. With the aid of the first-principles calculation, we are going to further explore the evolution of lattice during the spin reorientation. By analyzing the obtained results as mentioned above, the correlations among magnetoelastic coupling, spin reorientation and lattice distortion can be revealed. Finally, oxides with room temperature giant magnetoelastic coupling effect driven by small magnetic field can be discovered, and the physical mechanism of magnetoelastic coupling effect will be also found.

压磁现象和磁致伸缩是磁弹耦合效应的宏观表现。这些有趣的物理现象在自旋器件、声纳和应力传感器及超声换能器等领域有着重要的应用前景。本项目拟通过压力下的磁性表征、磁场/温度下的应变测试并结合中子衍射等手段来研究稀土正铁氧体RFeO3(R=稀土元素)体系自旋重取向相变所伴随的磁弹耦合效应。通过组分的调节和优化，获得较小外场驱动下，显示出较大的压磁和磁致伸缩效应的样品。以此为基础，在第一性原理计算的指导下，探索自旋重取向相变过程中晶格的演变过程，揭示磁弹耦合效应与自旋重取向及晶格畸变之间的关联，以期获得在室温和低场下具有优异磁弹耦合性能的氧化物材料，并掌握该类材料中磁弹耦合的物理机制。

本项目系统地研究了RFeO3体系自旋重取向及自旋构型的等静压调控，探究了该体系的磁结构耦合行为，系统并详尽的阐述了不同材料的自旋重取向相变的机理。在TmFeO3单晶中，我们通过等静压下的磁化及应变测试，澄清了自旋重取向相变过程中伴随着c方向收缩a方向伸长的结构相变，同时自旋重取向相变随着压力增大而展宽，这暗示着等静压不仅通过调控结构相变来调控磁相变的发生，在等静压的施加过程中，有中间相Γ1的出现。在NdFeO3单晶中，随着等静压的增大，相变类型由无等静压下Γ2-Γ4变为Γ2-Γ2+Γ1+Γ4-Γ1+Γ4-Γ4。通过高温高压热退火样品与未退火样品比较，我们发现退火使自旋重取向类型由Γ2到Γ4变为Γ2过量的Γ24到Γ4过量的Γ24。此外，本项目还对RFeMnO4（R为Er、Tm、Yb和Lu）体系的单晶生长、磁性、介电以及铁电性进行了初步探索。上述研究成果为深入理解RFeO3的自旋重取向相变并设计相应磁器件提供了重要的研究基础。