Teaching

# People

Sahar Goharshenasanesfahani

preparing to measure the beam power

Bharat Giri aligning the sample into focus

Mattias Scott-Jones checking the apertures

Farzaneh Hoveyda aligning the sample

in the magneto-optics lab (NS-05LL)

in the ultrafast optics lab (NS-123)

Richard Judge

preparing a pump-probe measurement

Erich Hohenstein optimizing data acquisition parameters

Sultan Alzahrani

# Ultrafast magnetism and thermal transport in nanostructures

Intense laser pulses can fragment the magnetization of a material. In contrast to the precession of an intact magnetization that can be described with classical equations of motion, the quantum time-evolution of a fragmented magnetization requires a different approach. Practical applications include minimizing the bit writing error rate in heat-assisted magnetic recording in materials with perpendicular magnetization.

We apply optical techniques to examine the non-equilibrium magnetization and temperature dynamics in thin metallic films in different experimental conditions and compare the results to model predictions and computer simulations. Films are deposited and characterized with instruments from the large suite of tools at the University of Louisville Micro and Nano Technology Center.

The research revealed that all-optical switching in thin metallic samples on glass substrates is driven by demagnetizing fields and thermal gradients, following full thermal demagnetization. Measurements made possible by heat accumulation probed simultaneously the equilibrium thermal demagnetization and the non-equilibrium ultrafast demagnetization dynamics in a temperature range from room temperature to above the Curie temperature.

Back-reflection echo of the strain wave in a thin nickel film

($1 ps=10-12s$).

Example of cumulative all-optical switching in Co/Pd superlattices. Dark and bright areas correspond to magnetization pointing up and down.

Correlation trace of the laser pulses ($1 fs=10-15s$). The pulse duration is a relevant and adjustable parameter.

Micromagnetic simulations can shed light on the magnetization time-evolution. To download a movie right-click on the image and save (it will play with VLC software)

The vertical stripe made in a Co/Ag heterostructure, disappears when crossing the horizontal stripe pattern, and reappears on the other side of the horizontal stack (above the top of this image).