Ultrafast demagnetization in NiCo2O4 thin films probed by time-resolved microscopy

Using a time-resolved magneto-optical Kerr effect microscope, we observed ultrafast demagnetization of inverse-spinel-type ferrimagnet NiCo2O4 (NCO) epitaxial thin films with perpendicular magnetic anisotropy. This microscope uses a pump-probe method, where the sample is pumped at 1030 nm, and magnetic domain images are acquired via magneto-optical Kerr effect microscopy at 515 nm (the second harmonic). We observed the dynamics of the magnetic domain of the NCO thin film via laser irradiation and obtained a demagnetization time constant of approximately 0.4 ps. This time constant was significantly smaller than the large time constants reported for other half-metallic oxides. This timescale of ∼0.4 ps agrees with the spin polarization of ∼0.7 determined by tunnel magnetoresistance [Shen et al., Appl. Phys. Lett. 117, 042408 (2020)].