Fig. 5. Zeeman splitting maps extracted from the ODMR data for the four NV center orientations within the diamond crystal. Due to the bias magnetic field, the absolute splitting contains corresponding offset values. Due to the strong magnetic field amplitude generated by the MNPs, the peak positions for different orientations slightly overlap in some areas resulting in a noisy image area. Comparing with 3a, (a) corresponds to NV₁ (b) to NV₂, (c) to NV₃ and (d) to NV₄.