Magneto-optical diffraction of visible light as a probe of nanoscale displacement of domain walls at femtosecond timescales.

Using diffraction of femtosecond laser pulses of visible light by a magnetic domain pattern in an iron garnet, we demonstrate a proof of concept of time-resolved measurements of domain pattern movements with nanometer spatial and femtosecond temporal resolution. In this method, a femtosecond laser (pump) pulse initiates magnetization dynamics in a sample that is initially in a labyrinth domain state, while an equally short linearly polarized laser pulse (probe) is diffracted by the domain pattern. The components of the diffracted light that are polarized orthogonally to the incident light generate several concentric diffraction rings. Nanometer small changes in the relative sizes of domains with opposite magnetization result in observable changes in the intensities of the rings. We demonstrate that the signal-to-noise ratio is high enough to detect a 6 nm domain wall displacement with 100 fs temporal resolution using visible light. We also discuss possible artifacts, such as pump-induced changes of optical properties, that can affect the measurements.

THz-Scale Field-Induced Spin Dynamics in Ferrimagnetic Iron Garnets.

THz magnetization dynamics of antiferromagnetically coupled spins in ferrimagnetic Tm_{3}Fe_{5}O_{12} is excited by a picosecond single-cycle pulse of a magnetic field and probed with the help of the magneto-optical Faraday effect. Data analysis combined with numerical modeling shows that the dynamics corresponds to the exchange mode excited by the Zeeman interaction of the THz magnetic field with the spins. We argue that THz-pump-IR-probe experiments on ferrimagnets offer a unique tool for quantitative studies of dynamics and mechanisms to control antiferromagnetically coupled spins.