Stress modulated antiferromagnetism in thin film heterostructures

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.