Enhanced Linearity in NiCo₂O₄ Epitaxial Thin-Film Based Magnetic Sensor Via Graphene Interfacial Modulation

Inverse spinel oxide NiCo 2 O 4 has attracted much attention in recent years because of its potential usage in building out-of-plane magnetized oxide spintronics. However, the perpendicular magnetic anisotropy and anomalous Hall effect (AHE) of NCO remain to be improved for the practical application of novel devices. In this paper, we propose a strategy to modulate the structure, and electrical and magnetic properties of the NiCo 2 O 4 epitaxial films by inserting a layer of graphene at the interface between the MgAl 2 O 4 substrate and the film. The insertion of graphene has not broken the epitaxial nature of the film, but has effectively modulated the grain size and strain state. Correspondingly, stronger room-temperature perpendicular magnetic anisotropy and anomalous hall resistance have been found in NiCo 2 O 4 /graphene/MgAl 2 O 4 -based standard Hall bar device. The linearity ([Formula: see text]) corresponds to the fit of Hall resistivity ([Formula: see text]) vs out-of-plane magnetic field ([Formula: see text]) in the range of 0–1[Formula: see text]T, demonstrating a strong linear relationship critical for magnetic sensing applications. In addition, it reveals that the insertion of graphene can change the sign of the AHE and increase the coercivity of the films at a low temperature. Our findings provide a viable route to design high-performance magnetic sensors with tunable linearity and temperature stability.