Viscous spin exchange torque on precessional magnetization in $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_{n}$ superlattices

TL;DR

This study investigates magnetization dynamics in LaMnO3/SrMnO3 superlattices, revealing exchange torque effects due to coupling between viscous and fast spins, with implications for understanding spin interactions in complex oxides.

Contribution

The paper introduces a model explaining the emergence of exchange torque as a coupling between viscous and fast spins in superlattices.

Findings

Monotonic frequency-field dependence in n=1 superlattice

Large precession frequency at low fields for n≥2 superlattices

Exchange torque arises from coupling between two spin populations

Abstract

Photoinduced magnetization dynamics is investigated in chemically ordered $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_n$ 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 $n\geq2$ 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.