Ultrafast magnetization dynamics in perovskite films and heterostructures

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In our proposal, we want to investigate photo-induced ultrafast spin dynamics in strongly-correlated perovskite thin films and heterostructures, together with their collective response of charge and lattice degrees of freedom. In particular, we are interested how photo-doping with ultrafast lasers can be used to suppress and enhance ferromagnetic order in these materials, and how femtosecond spin-currents act on the balance of different phases. In order to carry out such experiments, the femtosecond time-resolved magneto-optical Kerr effect is usually applied. However, as has been seen for many years, it is very often impossible to disentangle the photo-induced magnetic response of correlated materials from the electronic and lattice response in the measured Kerr signals. The reason is that the collective response of spins, electrons and lattice to a photo-excitation rapidly changes the refractive index of the material, which itself modifies the measured transient Kerr signal, so that the pure magnetic response cannot be extracted.In order to overcome this problem, and to extend the investigation of ultrafast spin dynamics towards correlated electron materials, we will apply new experimental methods in combination with studies on “contrast” film samples of perovskite oxides. First, we will use our recently developed ultrafast and element-specific magneto-optical Kerr technique in the extreme ultraviolet region of the spectrum, which is only marginally sensitive to changes of the refractive index, and, therefore, is an ideal probe of “pure” magnetization dynamics in correlated materials. In addition, recent progress in our understanding of transient Kerr signals in the visible range of the spectrum helps us to disentangle spin-, electron-, and lattice dynamics. Furthermore, using the metalorganic aerosol deposition technique, we will explore the unique possibility to prepare a multitude of thin perovskite oxide films with different composition and tuned electron-spin-lattice correlations. The in this way produced “contrast” samples will be examined with respect to their ultrafast spin dynamics, helping us to elucidate, for instance, the role of electron-phonon coupling on the (de)magnetization dynamics in optimally doped manganites. In the future, a distinct access to the photo-induced spin dynamics in correlated materials might open up an avenue of possible research directions, spreading from a deeper understanding of the non-equilibrium correlation physics towards generation of transient “hidden” states via photo-excitation.