Stress modulated antiferromagnetism in thin film heterostructures

在开发新的高密度逻辑和存储器件的挑战中，由于极低能耗器件的潜力，使用电子自旋输运作为数据矢量（即自旋电子学）的概念引起了极大的兴趣。反铁磁材料可以通过在铁磁和反铁磁之间的界面上的磁交换偏置现象在自旋电子器件中发挥关键作用。这种现象允许这种异质结构作为自旋阀，根据它们的自旋来控制电子的传导。调制交换偏置的能力，例如通过开关反铁磁性，将是自旋电子器件设计中一个有价值的概念。本项目研究了BiFeO3-PbTiO3固溶体中的这种反铁磁开关，表现出铁电性和反铁磁性，其中电极化和磁化通过晶格应变耦合。这种耦合在四边形和菱形对称的结构相变中表现得最为敏感。实验计划将集中于脉冲激光沉积和表征BiFeO3-PbTiO3成分的薄膜，在各种衬底上，导致电场和机械应力如何相互作用来调节反铁磁有序参数的理解。

In the challenge to develop new, high- density logic and memory devices, the concept of employing electron spin transport as the data vector (i.e. spintronics) is of great interest due to the potential for very low energy consumption devices. Antiferromagnetic materials can play a pivotal role in spintronic devices through the phenomenon of magnetic exchange bias at the interface between a ferromagnet and an antiferromagnet. This phenomenon allows such heterostructures to act as spin-valves to control the conduction of electrons according to their spin. The ability to modulate the exchange bias, for example by switching the antiferromagnetism on and off, would be a valuable concept in spintronic device design.This project investigates such antiferromagnetic switching in BiFeO3-PbTiO3 solid solutions, exhibiting both ferroelectricity and antiferromagnetism, in which the electrical polarization and the magnetization are coupled via the lattice strain. The coupling appears to be most sensitive at a structural phase transition between tetragonal and rhombohedral symmetries. The experimental programme will focus on the pulsed laser deposition and characterization of thin films of BiFeO3-PbTiO3 compositions, on a variety of substrates, leading to an understanding of how electric field and mechanical stress can interact to modulate the antiferromagnetic order parameter.