Fig. 3: Ultrafast control of magnetization.
From: Generation of ultrafast magnetic steps for coherent control
a, Sketch of the experimental geometry. A film of Bi:LIGG is placed on top of the same YBa2Cu3O7 disc shown in Fig. 2a. The disc is photoexcited with an ultraviolet laser pulse (λ = 400 nm) at T = 55 K < Tc to disrupt superconductivity. The magnetic field step generated (Fig. 2) triggers coherent magnon oscillations in the neighbouring Bi:LIGG sample. b, The data points show the time evolution of the changes in the z component of the Bi:LIGG magnetization ΔMz, quantified by measuring the Faraday rotation above the centre of the superconducting disc versus quench-probe delay. Each data point represents the mean value ± s.e.m. (smaller than the size of the data points) extracted from a sample of 360 acquisitions (Supplementary Section 5). The fluence of the quench pulse is ~0.3 mJ cm–2. At negative time delays, Mz equals –1.4 mT due to negative trapped flux before the pump pulse hits the YBa2Cu3O7 disc (Supplementary Section 14). The solid line shows a simulation of ΔMz above the centre of the YBa2Cu3O7 disc using a Landau–Lifshitz–Gilbert model and the magnetic field step shown in Fig. 2b as the input bias (Supplementary Section 15). c, Representation of the effective magnetic field (Heff) dynamics inside Bi:LIGG. Heff is given by the sum of a constant field accounting for shape anisotropy (HA) and the time-varying magnetic field step (Hstep) generated by photoexciting the adjacent superconducting disc. Hstep is negative at negative delays due to the trapped magnetic flux in the superconductor (Supplementary Section 14). d, Representation of the magnetization (M) dynamics in Bi:LIGG. Initially, M is aligned with Heff. The sudden change in Heff induces a precessional motion of M around the new direction of the effective field. At longer timescales, the magnetization aligns with the effective field.
