Manifestation of intra-atomic 5d6s-4f exchange coupling in photoexcited gadolinium

Abstract

Intra-atomic exchange couplings (IEC) between $5d6s$ and $4f$ electrons are ubiquitous in rare-earth metals and play a critical role in spin dynamics. However, detecting them in real time domain has been difficult. Here we show the direct evidence of IEC between $5d6s$ and $4f$ electrons in gadolinium. Upon femtosecond laser excitation, $5d6s$ electrons are directly excited, their majority bands shift toward the Fermi level while their minority bands do the opposite. For the first time, our first-principles minority shift now agrees with the experiment quantitatively. Excited $5d6s$ electrons lower the exchange potential barrier for $4f$ electrons, so the $4f$ states are also shifted in energy, a prediction that can be tested experimentally. Although a significant number of $5d6s$ electrons, some several eV below the Fermi level, are excited out of the Fermi sea, there is no change in the $4f$ states, a clear manifestation of intra-atomic exchange coupling. Based on our results, we propose that the demagnetization time of a material be inversely proportional to the density of states at the Fermi level and the excited, not the whole, spin moment. This can be tested experimentally.

arXiv comment18 pages, four figures, one supplementary material file

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Cited by in corpus (2)

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