Observation of giant topological Hall effect in Pt/NiCo₂O₄ heterostructure over wide temperature range

The spin configuration of materials significantly influences their transport characteristics. To investigate the potential emergence of novel spin structure in heterostructure of strongly spin-orbit coupled metal Platinum (Pt) deposited on ferrimagnetic NiCo2O4 (NCO)/MgAl2O4 (001) films with perpendicular magnetic anisotropy (PMA)[1], we studied the spin transport properties at various temperature with different NCO thickness (8-30nm). In addition to the anomalous Hall effect expected from NCO, we observed topological Hall effects (THE) before the coercive field (H_C). The magnitude of THE increases with increasing T and vanishes near transition temperature of NCO. These results indicate that interfacial Dzyaloshinskii Moriya interactions (iDMI) of NCO/Pt comes to play, and strong spin orbit coupling enhances the iDMI[2] and becomes influential to compete with exchange interaction to form skyrmions. Based on the measured THE, the maximum estimated skyrmion density is 10³ at 270K for 16 nm thick NCO sample.

[1] C. Mellinger, J. Waybright, X. Zhang, C. Schmidt, and X. Xu, “Perpendicular magnetic anisotropy in conducting NiCo2 O4 films from spin-lattice coupling,” Phys. Rev. B, vol. 101, no. 1, p. 14413, 2020, doi: 10.1103/PhysRevB.101.014413.

[2] A. Fert, V. Cros, and J. Sampaio, “Skyrmions on the track,” Nat. Nanotechnol., vol. 8, no. 3, pp. 152–156, 2013, doi: 10.1038/nnano.2013.29.