Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields

We present a comprehensive experimental and numerical study of magnetization dynamics triggered in a thin metallic film by single-cycle terahertz pulses of $\sim20$ MV/m electric field amplitude and $\sim1$ ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect (MOKE), and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing table-top terahertz sources.Comment: 6 pages, 4 figure

Inertial spin dynamics in ferromagnets

The understanding of how spins move and can be manipulated at pico- and femtosecond timescales has implications for ultrafast and energy-efficient data-processing and storage applications. However, the possibility of realizing commercial technologies based on ultrafast spin dynamics has been hampered by our limited knowledge of the physics behind processes on this timescale. Recently, it has been suggested that inertial effects should be considered in the full description of the spin dynamics at these ultrafast timescales, but a clear observation of such effects in ferromagnets is still lacking. Here, we report direct experimental evidence of intrinsic inertial spin dynamics in ferromagnetic thin films in the form of a nutation of the magnetization at a frequency of ~0.5 THz. This allows us to reveal that the angular momentum relaxation time in ferromagnets is on the order of 10 ps

Micromagnetic measurements of ferromagnetic materials: Validation of a 3D numerical model

This work if focused on (nondestructive) micromagnetic measurements for ferromagnetic materials in view of Material Characterization (MC). The interest in micromagnetic measurements arises from their correlation to mechanical properties. It is well known that the microstructure of a material affects both mechanical and magnetic properties, therefore it is possible to infer mechanical properties from micromagnetic measurements. This is very convenient because micromagnetic measurements canbe carried out ina fast, cheap and nondestructive manner, if compared to mechanical measurements. To date, a lot of experimental workhas been carried in the past years but there is still some lack of proper numerical models capable of modelling micromagnetic measurements, especially when considering 3D models.Inthispaperwepresentanexperimentalvalidationofanad-hoc3Dnumericalmodelcapableofmodellingtheresponseinmicromagneticcharacterizationof ferromagnetic materials