In Operando investigation of barium titanate based oxide multiferroic nanostructures – IOBTO

The goal of this project is to grow and investigate technologically pertinent artificial multiferroic thin films and embedded nanostructures tailored to the need for advanced characterization techniques. We want to investigate the magneto-electric coupling in multiferroic systems and in particular the coupling of ferromagnetic and ferroelectric domains and domain walls under operation in static and dynamic electrical and/or magnetic excitation. Our model structures can reasonably be considered as elementary building blocks of technologically relevant structures that are likely to be involved in the next generation of multiferroic devices that will find their place in a large panel of genuine devices (e.g. magneto-electric memories cells, switchable ferroelectric barrier tunnel junctions and domain wall motion controlled information storage). These studies will be a first step in the in-depth understanding of the magneto-electric domain coupling as well as the basis for the design of new original devices that have high potential in the framework of new information technologies. Such measurements are very challenging and would constitute a major scientific breakthrough in the field.
The IOBTO project proposes a fundamental approach to the study in operando of artificial multiferroic structures using advanced characterization methods available on large scale facilities. We propose to elaborate fully epitaxial layers and nanostructures of ferrites – at the interface of – or embedded in barium titanate (BaTiO3) epitaxial layers grown by atomic oxygen assisted molecular beam epitaxy. Such structures have the advantage of being relevant from an application point of view but can still be considered as model single crystalline systems allowing the use of the most advanced characterization methods with the highest possible level of output. We want to investigate the coupling between ferroelectricity and ferromagnetism in these multiferroic systems and in particular the coupling of domains and domain walls under operation in static and dynamic electrical excitation.
The combination of ferro -electric and -magnetic compounds to elaborate artificial multiferroics has been demonstrated in recent years to be a fruitful approach to overcome the lack of intrinsic single phase multiferroics; which are rare and mostly without adequate properties (too small magneto-electric coupling coefficients, small Curie temperatures…). This new class of composites multiferroics rise however a number of new and challenging problems. In particular the interaction at the ferroelectric/ferromagnetic interfaces has to be elucidated from elastic/magnetic and electronic structure points of view. Beyond the proof of concept, the cross-boundary coupling coefficient will determine the usefulness of the grown heterostructures. The question becomes even more challenging when considering the investigation in operando by applying a static (DC) or dynamic (AC) electrical field during investigation.
In the IOBTO project we will produce dedicated "on demand" samples adapted to the individual constraints of each advanced characterization technique, which will include state of the art spectromicroscopy (X-PEEM), micro-diffraction, and X-ray absorption (XAS, XMCD) under variable electrical field. The combination of these techniques will provide a unique picture of the impact and coupling phenomena on the electronic and crystalline structures as well as on the magnetic domain structure and boundaries under operation. The consortium includes specialists of the growth of such systems as well as experts in the use of the each advanced characterization methods. Fully oxide samples present the advantage high stability in atmosphere and of possible operation in harsh environments. Moreover these systems are of a phase separation type warrant high chemical stability. All materials are chosen to be technologically relevant and environment friendly.