Studying magnetization configurations of ever more complex magnetic structures has become a major challenge in the past decade, especially at ultrashort timescales. Most of current approaches are based on the analysis of polarization and magnetization-dependent reflectivity. We introduced a different concept, centered on the coupling of magnetic structures with light beams carrying orbital angular momentum (OAM), which was recently tested it in an experiment with magnetic vortices. Upon reflection by a magnetic vortex, an incoming beam with a well-defined OAM ℓ gets enriched in the neighboring OAM modes ℓ ± 1. It results in anisotropic far-field profiles, which leads to a magnetic helicoidal dichroism (MHD) signal. In this paper we provide a detailed analysis of MHD for the case of a magnetic vortex, providing an intuitive explanation in terms of transverse MOKE. The analysis of MHD allows to retrieve the complex magneto-optical constants. This method, which does not require any polarimetric measurement, is a new promising tool for the identification and analysis of magnetic configurations such as vortices, with a possible extension to the femtosecond to attosecond time resolution.
C. Spezzani, E. Ferrari, E. Allaria, F. Vidal, L. Lounis, A. Ciavardini, R. Delaunay, F. Capotondi, E. Pedersoli, M. Coreno, C. Svetina, L. Raimondi, M. Zangrando, R. Ivanov, I. Nikolov, A. Demidovich, M. Danailov, G. De Ninno, H. Popescu, M. Eddrief, M. Kiskinova, M. Sacchi
Magnetization control without applying magnetic fields has potential for applications in sensors and devices. In Fe/MnAs/GaAs(001), the Fe magnetization can be modified by acting on the MnAs microstructure via temperature control, without applying external magnetic fields. Here we use an optical laser pulse to vary the local temperature and an x-ray free-electron laser pulse to probe the induced magnetic and structural dynamics in a time-resolved resonant scattering experiment, both pulses having ~100 fs duration. Modifications of the MnAs microstructure take place within a few ps, followed by a slower dynamics driven by thermal diffusion. We show that a single optical laser pulse can reverse the Fe magnetization locally, the process being driven not by the fast modifications of the MnAs structure, but rather by its slower return to equilibrium.
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