Fundamental aspects of all-optical single pulse switching in nanometer-sized magnetic storage media

• Applicant: Dr. Jakob Walowski
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 439225584

Increasing amounts of data for digital storage, call for new technological concepts enabling higher densities with faster writing speeds to the storage media. After over 40 years of miniaturization, conventional techniques for magnetic data storage are facing their limits. Essentially, storing information on a magnetic hard disk is setting the magnetization of smallest domains and thus creating bits. Conventionally, this is done by small electromagnets flying directly above the disk’s surface inducing a magnetic field. As the optimization possibilities using this method are technologically reaching an end, new approaches become interesting. All-optical helicity-dependent magnetization switching (AO-HDS) has the potential for further bit shrinking and at the same time to speed up the writing process. Our precedent studies with granular FePt hard disk media point to stochastic switching triggered by the Inverse Faraday Effect (IFE) as the major source of the deterministic switching mechanism with circularly polarized laser pulses, which we will overcome. I propose a research project performing AO-HDS switching experiment using circularly polarized femtosecond laser pulses in the wavelength range from near-infrared to midinfrared. In this study, the efficiency of the IFE with respect to different photon energies in granular media together with the interplay between the IFE and the magnetic circular dichroism will be elucidated. Using my expertise in time-resolved magneto-optical Kerr-effect (TR-MOKE) measurements will allow implementing these experiments alongside to further analyze the magnetization and switching dynamics on femto- to picosecond time scales. For the examination of plasmonic and dielectric near field amplification and switching enhancement, the required nanostructures at the interface to the disk media will be developed. Two collaborations with experimental groups will extend the analysis of the switching experiments by employing Kerr-Microscopy to image the magnetic structures after switching and to study the microscopic mechanism and origin of AO-HDS using Magnetic Force Microscopy. This project is embedded into existing successful theory collaborations in which the current tools developed for thermal spin modelling, ab-initio IFE calculations and thermal macrospin modelling will be extended to enhance their descriptive spectrum.

• DFG Programme: Research Grants