New physics often occurs at boundaries or regions of asymmetry.  One example is novel magnetization dynamics in superlattices composed of alternating layers of LMO and SMO.  In this experiment (a), we apply a magnetic field, H, nearly normal to the sample surface, and detect changes in the magnetization (example shown in b) with the time-resolved magneto-optical Kerr effect (TR-MOKE).  Example data is shown in panel (c).  

By extracting the precession frequency from the observed dynamics, we can gain insight into new physics at the boundary of two complex interfaces.  In this experiment, we investigated the precession frequency of a LMO2n/SMOn superlattice, with n = 1,2,3, as a function of applied field strength (shown in panels (a), (b), and (c), respectively).  For cases of n>1, we observed an unexpected increase in the precession frequency at low fields, indicating the presence of an additional exchange torque caused by coupling between two spin populations: a slow or viscous spin group, caused by frustrated bonds and disorder at the interface, and a fast spin group, comprised of bulk spins. 

Funding: DOE