Dynamic processes in magnetoelectrics – DYNAMECS

The complexity of magnetoelectric coupling mechanisms and the coexistence of different ferroic orders on nanometer length scale (e.g., in a domain wall or at the interface between two thin films) calls for the application of advanced techniques. For this purpose, DYNAMECS suggests the development and the combination of primarily optical methods, both linear and nonlinear, which are particularly suited for time-resolved measurements. The possibility to combine these methods with microscopes (wide field or confocal) allows us moreover to access the ferroic domains (magnetic, ferroelectric, and magnetoelectric/ferrotoroidal).

DYNAMECS has succeeded in developing a method that allows to selectively study different mechanisms of magnetoelctric coupling. We could thereby demonstrate that in Co/PZT bilayers the magnetoelastic coupling can be reduced by more than 50 % with increasing frequency, while the interfacial coupling remains unchanged.
Another remarkable result obtained by DYNAMECS is the observation of internal (bulk) ferroelectric domain walls, investigated with SHG nonlinear microscopy. This result corroborates theoretical predictions concerning the possibility of non-Ising type internal domain walls and it proves the existence of Néel and Bloch type domain walls in ferroelectrics.

We anticipate DYNAMECS to provide a variety of outcomes, including efforts to:
- develop a unique combination of facilities and expertise in time-resolved imaging methods to study both quasi-static and dynamic processes in magnetoelectrics;
- probe original switching effects that possibly could not be evidenced with standard techniques;
- gather a knowledge support on fast magnetic/electric switching in magnetoelectrics;
- generate interest among a wide research community working in material science magnetism, photonics, spintronics and instrument/method developments.

This project has led to the development of experimental measurement setups which are especially suited to study the magnetoelectric coupling. These experimental systems are currently accessed in the context of various scientific collaborations since 2014, for instance as a part of the GdR OXYFUN. The project has moreover resulted in five publications and 14 communications, three of which were invited talks of the PI. Two international workshops have also been co-organized by the PI in 2013 and 2015.

New trends in nanomagnetism involve the magnetization switching by means of spin polarized currents or by electrical fields instead of magnetic fields. The coupling between coexisting magnetic and electric orders in magnetic multiferroics makes these materials promising candidates for such electrical manipulation of the magnetization. In addition, ultrafast laser-induced magnetization reversal has been recently demonstrated in magnetic films. This electrical and/or optical manipulation of the magnetization in magnetoelectrics will likely inspire the design of new ultrafast magnetoelectric memory devices. Besides the potential for applications, fundamental research at the interface between optomagnetism and spintronics is expected to improve our knowledge of switching dynamics in magnetolectric multiferroics down to the sub-ps range.
Similar to the case of ferromagnetism or in ferroelectrics, where the scientific community has made considerable efforts for more than one decade to improve the understanding of dynamical processes and to explore the ultimate switching speed, such questions equally arise in magnetoelectric materials. The intricate coupling between magnetic and electric orders and the emergence of new functionalities at ferroic domain walls (such as, e.g., conductivity in insulating oxides, polarization in non-polar adjacent domains or local ferromagnetism in boundary regions of antiferromagnetic domains) makes it difficult to probe the switching dynamics or the propagation kinetics in such multiferroic nano-elements. The possibility to access different order parameters and to study their coupling and dynamics with both temporal and lateral resolution are major goals in the framework of DYNAMECS.
DYNAMECS aims primarily at studying dynamic processes in magnetoelectrics, by combining various advanced experimental techniques and simulation studies. In particular, time-resolved nonlinear optical second-harmonic generation microscopy (SHG) is employed to probe different ferroic orders (magnetic, ferroelectric and magnetoelectric/ferrotoroidic) at different temporal regimes, namely: quasi-static (> microsecond), dynamic (ns), and ultrafast (sub-ps). Particular attention will be drawn to laser-induced ultrafast switching in magnetoelectrics.