Photoinduced magnetization dynamics is investigated in chemically ordered (LaMnO3)2n/(SrMnO3)n superlattices using the time-resolved magneto-optic Kerr effect. A monotonic frequency-field dependence is observed for the n=1 superlattice, indicating a single spin population consistent with a homogeneous hole distribution. In contrast, for n≥2 superlattices, a large precession frequency is observed at low fields indicating the presence of an exchange torque in the dynamic regime. We propose a model that ascribes the emergence of exchange torque to the coupling between two spin populations -- viscous and fast spins.
@article{arxiv.0706.2157,
title = {Viscous spin exchange torque on precessional magnetization in $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_{n}$ superlattices},
author = {H. B. Zhao and K. J. Smith and Y. Fan and G. Lüpke and A. Bhattacharya and S. D. Bader and M. Warusawithana and X. Zhai and J. N. Eckstein},
journal= {arXiv preprint arXiv:0706.2157},
year = {2016}
}