Fig. 4: 3D FFT spectra of the 3D magnetic images of the Nd-Fe-B permanent magnet sample.

Cross sections in the (qx-qy), (qy-qz), and (qx-qz) planes are shown with line profiles along the (qx, 0, 0) and (0, 0, qz) directions. a, b Thermally demagnetized state and coercivity state at μ0H = −2.7 T, respectively. Inset (a) a central part of the FFT spectrum in the (qx-qz) plane with an expanded color scale. Back triangles indicate the peak positions of the line profiles.