Ultrafast Magneto-Acoustics in Nickel Films

TL;DR

This paper demonstrates the existence of ultrafast magneto-acoustic pulses in nickel films induced by femtosecond laser pulses, revealing strong coupling between acoustic waves and magnetization dynamics, leading to magnetization precession.

Contribution

It introduces the observation of magneto-acoustic pulses in nickel films and explains their coupling mechanism with magnetization using ultrafast laser excitation.

Findings

Magneto-acoustic pulses propagate in nickel films upon femtosecond laser excitation.

These pulses can induce magnetization precession via lattice deformation.

The coupling mechanism involves transient changes in crystalline anisotropy.

Abstract

We report about the existence of magneto-acoustic pulses propagating in a 200-nm-thick ferromagnetic nickel film excited with 120 fs laser pulses. They result from the coupling between the magnetization of the ferromagnetic film and the longitudinal acoustic waves associated to the propagation of the lattice deformation induced by the femtosecond laser pulses. The magneto-acoustic pulses are detected from both the front and back sides of the film, using the time-resolved magneto-optical Kerr technique, measuring both the time dependent rotation and ellipticity. We show that the propagating acoustic pulse couples efficiently to the magnetization and is strong enough to induce a precession of the magnetization. It is due to a transient change of the crystalline anisotropy associated to the lattice deformation. It is shown that the results can be interpreted by combining the concepts of acoustic pulse propagation and ultrafast magnetization dynamics.