fig2

Figure 2. Structural characterization and spin-dependent performance of heterostructures. (A) Atomic force microscopy (AFM) image of the NiCo₂O₄/MgAl₂O₄ (NCO/MAO) bilayers with a root-mean-square (RMS) roughness of 0.05 nm. The length of the scale bar is 1 μm; (B) X-ray diffraction (XRD) patterns of MAO (12 nm), NCO (16 nm), and NCO (16 nm)/MAO (3 nm). The characteristic diffraction peaks at (004)-plane are indicated; (C) Reciprocal space mapping (RSM) of the (408) reflection of the NCO/MAO bilayers; (D) Annular bright-field (ABF) micrograph of the magnetic tunnel junction (MTJ) heterostructures along the [100] axis, with labels indicating different layers. The length of the scale bar is 20 nm. Inset: Atomic-resolution higher-magnification high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the region enclosed by the red dashed box, illustrating the unit cell scheme of the NCO crystal structure. Red and blue spheres represent T_d and O_h sites, respectively; (E) Schematic illustration of hall-bar device for anomalous Hall effect (AHE) measurements; (F) AHE loops of the Co₈₂Gd₁₈ (5 nm)/Pt (50 nm) bilayers at various temperatures; (G) AHE loops of the NCO (16 nm)/MAO (3 nm) bilayers at different temperatures; (H) Out-of-plane magnetic hysteresis loops of the NCO/MAO bilayers, Co₈₂Gd₁₈ /Pt bilayers, and MTJ heterostructures at 10 K. BF: Bright-field.