Time-resolved probing of magnetic and magneto-acoustic excitations

Place: IMDEA Nanociencia conference hall.

Abstract: 

Hybrid quasi-particles in condensed matter systems are observed at the degeneracy points between
different degrees of freedom exhibiting non-zero coupling. These solid-state chimeras could be exploited in
a wealth of applications, ranging from transducers to sensors, to memory and logic units [1]. In particular,
when the dispersion relation of phonons and of magnons are degenerate, magnetostriction can allow for
efficient cross-talk between lattice and spin reservoirs in the few gigahertz range. Notably, such degeneracy
can take place at finite wavevector: suitable experimental methods to investigate the dispersion relation in
the vicinity of the mode crossing are called for.
I will present recent experimental results on finite-wavevector magneto-acoustics in ferromagnetic thin film
and nanostructures [2]. The systems have been investigated via optical Transient-Grating (TG) spectroscopy
and time-resolved MOKE at NFFA-SPRINT laboratory (Trieste) [3]; correlative characterization of the samples
via ferromagnetic resonance, Brillouin scattering and micromagnetic simulations further confirm the
observed dynamics and allow to draw the boundary for reliable data interpretation. Hamiltonian modelling
of the mode crossing allows to quantify the magnon-phonon coupling strength and the degree of coherence
in the coupling.
Impulsive photon-driven excitation of finite-wavevector excitations can be fruitfully extended down to the
mesoscopic scale, e.g. by FEL-based TG spectroscopy, a technique that is getting growing attention from the
scientific community [4-5]. I will present experiments conducted in collaboration at FERMI FEL (Trieste) and
Eu-XFEL (Hamburg) which aim at establishing X-ray TG spectroscopy as a routine tool for condensed matter
physics.