Phase-Dependent Energy Dissipation Processes in La0.7Sr0.3MnO3 and (La0.6Pr0.4)0.7Ca0.3MnO3 after an Ultrashort Optical Excitation

by Cinja Seick
Doctoral thesis
Date of Examination:2022-09-28
Date of issue:2023-08-31
Advisor:Prof. Dr. Stefan Mathias
Referee:Prof. Dr. Stefan Mathias
Referee:Prof. Dr. Christian Jooss
Referee:Prof. Dr. Thomas Weitz
Referee:PD Dr. Oliver Bünermann
Referee:PD Dr. Martin Wenderoth
Referee:Prof. Dr. Michael Seibt
Persistent Address: http://dx.doi.org/10.53846/goediss-10075

 

 

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Abstract

English

La0.7Sr0.3MnO3 (LSMO) and (La0.6Pr0.4)0.7Ca0.3MnO3 (LPCMO) are perovsikte manganites which both show a ferromagnetic-to-paramagnetic phase transition. Interestingly, the development of the new phase when crossing the phase transition occurs due to two different polaronic effects in both systems: correlated Jahn-Teller polarons in the case of LPCMO and large polarons in the case of LSMO. In order to investigate the changes of energy dissipation which are caused by the two different phenomena, pump-probe experiments in the optical regime are performed to excite dynamics at the fs-timescale. The following dynamical evolution of both systems is studied up to 1.1 ns after the excitation by applying different external stimuli to both systems. With the help of the resulting temperature, fluence, and magnetic field dependencies, suggestions for the underlying processes of the four experimentally found dynamical steps are discussed. To obtain the electronic and a partially phononic response, as well as the contributions by the spin system, two different kinds of time-resolved techniques are used experimentally: transient reflectivity and time-resolved magneto-optical Kerr effect, both measured simultaneously. Detailed static characterizations of the thin film samples as well as finite-difference timedomain simulations based on an one-dimensional 3 temperature model support the hypotheses which are deduced from the dynamical experiments. Thereby, the focus spots onto the excitation transitions where two different kind of excitation steps are suggested as well as onto the relaxation mechanisms back to the ground state where similar behavior are observed.
Keywords: LSMO; LPCMO; perovsikte manganite; ultrafast magnetism; electron dynamics; TRMOKE; transient reflectivity; energy dissipation
 
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