The c-axis out-of-plane Kerr view of SMP and MMP magnets. Magneto-optical Kerr images of thermally demagnetized (a) SMP magnet with 9 wt.% La–Ce and (c) MMP magnet with 18 wt.% La–Ce. The average domain width in the MMP magnet is almost twice the size of the SMP one. The pink arrows in (c) depict the domain clusters that joint together with ∼ 20 μ m wide, and are obviously larger than the average grain size ( ∼ 6.5 μ m ), indicating a strong exchange coupling within the 2:14:1 grains and long-range magnetostatic interactions in the MMP magnets. The corresponding domain patterns under 600 mT (parallel to c-axis) are shown in (b) and (d). The intersecting domain group changes barely, suggesting a higher stability of the MMP magnet in preserving its virgin domain patterns than the SMP one. The box areas A, B, C and D are pointed out for comparisons.^[22]