Elemental asymmetries of spin and electron dynamics in an insulating ferrimagnet

Abstract

NiFe2O4 has gained significant attention from the scientific community due to its potential applications in microwave integrated devices, magnetoelectric coupling heterostructures, and spintronic devices such as spin filters. In this work, we explore the element specific ultrafast dynamics of NiFe2O4 films grown on ZnGa2O4 and MgAl2O4 with different lattice mismatches. To examine the dynamics, we utilize the transverse magneto optical Kerr effect at the extreme ultraviolet (XUV) regime, which provides access to the Fe and Ni M-edges. The demagnetization is almost concurrent with the pump pulse, suggesting that slower phonon based interactions are not crucial for the demagnetization. The reflectivity of the MAO sample is significantly higher than for the ZGO sample, which correlates well with the increased amount of free carriers. Furthermore, the reflectivity exhibits pronounced oscillations in both the Fe and Ni signals with a period of ∼2.8 ps (0.36 THz). Notably, the onset of the oscillations of the Fe is delayed by about 0.2–0.5 ps with respect to the Ni.