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• W1572320526 abstract "Including the spin degree of freedom into electronic circuits e.g. as non-volatile memory devices, requires the exact knowledge of the speed with which writing information is possible. All-optical pump-probe experiments with ultra-short pulses generated by Ti:Sapphire lasers give insight into magnetization dynamics on the femtosecond time scale. The magnetization dynamics is triggered by heating the electron system with the intense pump pulses and demagnetizing the system. The demagnetization and subsequent relaxation into the initial state are probed with much weaker probe pulses using the magneto-optical Kerr-effect. In this thesis the ultrafast demagnetization and magnetization recovery were investigated in nickel thin films (2 nm to 40 nm), applying pump fluences from 10mJ/cm2 to 50mJ/cm2. The relative demagnetization was determined from the quenching of the Kerr rotation extracted from hysteresis loops recorded before heating and during maximum demagnetization. Additionally, reflectivity dynamics was measured using the same setup with a different detection scheme to determine the electron temperature during the demagnetization and recovery process. For a quantitative analysis the analytic solution to the Three-Temperature-Model was fitted to the data to extract the demagnetization and recovery times. Magnetization dynamics can be modeled using the Landau-Lifshitz-Bloch equation. The only parameter needed is the electron temperature, which can be obtained independently from the reflectivity experiments. For the 15 nm nickel film the modeled data shows very good agreement with the experimental data. For the other nickel film thicknesses, the reflectivity data are discussed from the perspective, how the extracted electron temperatures are useful as input for modeling with the Landau-Lifshitz-Bloch equation, to obtain results in agreement with the experimental data. Additionally, further models, namely the micro-magnetic three temperature model m3TM and the spin super-diffusion which describe the magnetization dynamics, are discussed and compared. The next step to improve energy efficiency of microprocessor chips will be achieved by using the heat produced during computation as an additional power source to run those processors. This technique together with the utilization of the electron spin in electronic devices is termed spin caloritronics. In this context magnetic tunnel junctions are interesting devices as nonvolatile memory units. They can be read out using voltages generated by temperature gradients created by utilizing the heat produced during operation. There, different voltages are generated depending on the relative magnetization of both magnetic layers in the tunnel junction, termed magneto-Seebeck effect. In this thesis the magneto-Seebeck effect was investigated in CoFeB-MgO-CoFeB junctions by creating the temperature gradient across the junction heating one side of the junction optically using a laser. The realization of the setup is described in detail. The experimental data is compared to ab-initio calculations of the magneto-Seebeck effect." @default.
• W1572320526 created "2016-06-24" @default.
• W1572320526 creator A5059867103 @default.
• W1572320526 date "2022-02-20" @default.
• W1572320526 modified "2023-10-05" @default.
• W1572320526 title "Physics of laser heated ferromagnets: Ultrafast demagnetization and magneto-Seebeck effect" @default.
• W1572320526 doi "https://doi.org/10.53846/goediss-2944" @default.
• W1572320526 hasPublicationYear "2022" @default.
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