The speed of magnetic data storage and information processing is presently limited to a few nanoseconds for a writing process. In this context, the use of ultrashort laser pulses is the most promising tool to overcome this limitation. Femtosecond lasers drive magnetization dynamics covering a wide range of time and length scales, from femtosecond demagnetization and picosecond switching to the nanosecond recovery to equilibrium, involving highly localized spin excitations as well as the dynamics of magnetic domains at the microscale. Optical femtosecond laser pulses have been shown to induce picosecond switching in only some specific ferrimagnetic rare-earth transition metal alloys. Despite intense research in the field, full understanding of the underlying processes is still missing. Open questions are as follows: How does angular momentum and energy dissipate in two-sublattice magnets, such as antiferromagnets and ferrimagnets? What is the role of the specific rare-earth on switching? Can we find a universal spin model to describe both the ultrafast spin dynamics of rare-earths and the successive slower magnetic domain growth and motion? How does the latter in turn depend on the initial ultrafast dynamics and the overall spin structure of the magnet?
To address these questions, we aim to develop and use an advanced multi-scale environment for the modelling of ultrafast spin dynamics experiments in ferro-, ferri- and antiferromagnetic nanostructured materials. To this end, we will focus on rare earths, transition metals, and their combinations in heterostructures. Our goal is to investigate the way ultrashort optical laser pulses, intense THz pulses, and fs spin current pulses control magnetic order at the picosecond time scale. Those dynamics will be investigated by atomistic spin dynamics methods, parametrized from data of first principles calculations. On that basis, the slower temporal evolution of magnetic domains will be studied by micromagnetic models using as input parameters the results of the atomistic spin dynamics calculations. The expectation is that the computational model will go beyond the current state-of-the-art theories to not only describe experimental observations but also to provide theoretical predictions.
Ultrafast magnetization dynamics at very high magnetic fields and elevated temperatures
Phys. Rev. B 98, 014417 (2018) - DOI: 10.1103/PhysRevB.98.014417