Applied Physics Seminar: " Electric field Control of Magnetism"

Complex oxides have fascinated the scientific community for years due to the rich physics and the often-unique phenomena displayed by these materials. More specifically, complex perovskite oxides have been studied intensively as of the past few decades due to the vast collection of functional (even multifunctional) electronic phases observed in this class of materials (magnetism, ferroelectricity, superconductivity, and other highly correlated electron behavior). Due to this collection of electronic phases, the complex oxides offer unparalleled opportunities for investigating and defining functional properties in engineered heterostructures and devices.

Modern magnetic memory technology is faced with issues of scalability and energy consumption as the required electrical current causes significant heating and stray magnetic fields. An ideal solution to this problem would be a magnetic device that can be controlled with an electric field in a capacitor structure as the electric field is well confined and minimal energy is dissipated. One issue is that the switching a magnetic device requires breaking time reversal symmetry, a symmetry that is broken by an applied current or magnetic field but not by an applied electric field. There is a set of complex oxide perovskites, known as multiferroics, which possess both a ferroelectric polarization and a (anti)ferromagnetic order. Furthermore, a multiferroic is deemed magnetoelectric when these two orders are coupled together. These materials then open pathways towards the electric field control of magnetism which ultimately depends on the mechanism of magnetoelectric coupling.

Unfortunately, these materials are exceedingly rare. Currently, there is only one multiferroic with unambiguous magnetoelectric coupling at room temperature (BiFeO3). I will discuss the local magnetoelectric switching of an anisotropically strained multiferroic BiFeO3 film in response to an electric field. The switching is influenced by the mechanical and electrical boundary conditions set by the substrate and the domain structure of the film matrix. A heterostructure of BiFeO3 and a ferromagnetic metal – Co0.90Fe0.10 – is used to probe the magnetic structure of the multiferroic and the predicted multistage magnetoelectric switching which is capable of reversing the ferromagnetic moment of the exchange coupled ferromagnet. This result has the potential to impact spintronics and magnetic based logic and memory.

Lastly, I will discuss our current research directions within the field of ferroic oxides.