Understanding and Controlling Magnetic
Damping Behaviour in Synthetic
Ferromagnetic Thin-Film Multilayers

Abstract

Magnetisation precessional dynamics have a great role in ferromagnetic thinfilms
and nanostructures, where the underlying mechanisms of intrinsic and extrinsic
damping are crucial for spintronic and magnonic devices. This important role
drives the research activity with a goal of acquiring a better understanding and the
ability to tune magnetic damping properties as desired. Research has tackled these
issues through many routes linked with the ferromagnetic material type or thickness,
while others have tried different aspects by including other nonmagnetic or
ferromagnetic elements as dopants or adjacent layers.
The effect of the additional nonmagnetic materials on the magnetic damping in
ferromagnetic system is the focus in this thesis, where a range of implementations of
the nonmagnetic material was studied. The role of nonmagnetic layer on damping
is shown in this study as the evolution of damping as the thickness of this capping
layer developed gradually from none to a partial and to a full covering layer. The
effect of nonmagnetic elements was also shown when the changes of the interface
takes place, the magnetic damping depends on the development of the interface
and the reduction of the NM capping layer is also demonstrated. These routes helps
to establish an understanding of damping and the underlying mechanisms.
Linking magnetic damping with other dynamic magnetisation phenomena gives
an insight into the reversal behaviour mediated by domain walls in ferromagnetic
systems. Studying jointly the contributions of damping and interfacial Dzyaloshinskii-
Moriya Interaction gives a better insight into the factor effecting the magnetisation
dynamics. As the understanding of the magnetic damping became clearer and the
underlying mechanism and effects, linking between two-magnon scattering, spinpumping
and spin-mixing conductance with the crystal structure give more information.
This understanding and theory initiated a study to test the theory with a
new route to control magnetic damping through modifying the contributions to the
total magnetic damping that come from the individual atomic layers that make up
a ferromagnetic thin-film. This showed outstanding results consistent with theory
and demonstrating very low damping in a new synthetic ferromagnet.