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The domain structures have been found to be different in the Sm(CobalFe0.1CuxZr0.033)6.9magnets (x = 0.07, 0.10, 0.13) with the abnormal and normal temperature dependence of coercivity by quenching at 400 °C and 600 °C, respectively. In the magnets with abnormal temperature dependence of coercivity, the domain structure shows more like the strip domain which is typical domain shape of the ferromagnets of easy-axis anisotropy, while the domain structure becomes narrower and shows more additional domains in the magnets with normal temperature dependence of coercivity. The difference of the domain structure can be attributed to whether the Cu is homogeneous in the 1:5 cell boundary phase, and this will lead to different domain wall pinning and different temperature dependence of coercivity in the magnets according to the noncontinuous domain wall pinning model. As the Cu is nearly homogeneous in the 1:5 cell boundary phase, the domain wall should be pinned near the interface between 2:17 cell phase and 1:5 cell boundary phase, and the coercivity shows abnormal temperature dependence. On the contrary, the domain wall should be pinned into the 1:5 cell boundary phase, where a gradient of Cu content exists, leading to the normal temperature of coercivity.
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