Intersublattice exchange interaction probed with high order harmonics over multiscale dynamics

Time Friday, October 26th, 10:10
Speaker: Marie BARTHELEMY, Strasbourg

Over the past few years, optically induced ultrafast magnetization dynamics has been investi-gated in alloyed ferromagnets by probing core level to 3d band optical transitions of transition metals [1,2]. Those chemical selective measurements are sensitive to the sub-lattices interaction processes during the transient magnetization dynamics. For example, it has been found that the inter-sub-lattice exchange interaction has to be taken into account if the demagnetization times of each sub-lattice of the ferromagnet are considered [3,5]. In this work, permalloy sub-lattices magnetic momenta dynamics are measured simultaneously with a table top Transverse Magneto Optical Kerr Effect by probing with High order Harmonics (20-70 eV range) over a broad tempo- ral scale (Figure1). The Landau-Lifshitz-Bloch equation associated to Langevin formalism can be used to deduce the demagnetization time t ε attributed to each element ε, by taking exchange interaction into account [5]. From our measurements in permalloy, both elements demagnetize simultaneously and precess in phase with same period and Gilbert damping due to strong exchange interaction. It will be shown that the ratio between effective exchange interaction constants of Ni and Fe can be retrieved from those measurements. Moreover, the dependence of relaxation rate upon the pump density of excitation will be discussed considering a multiscale approach including tem-perature dependent exchange parameters.

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