Microstructure, electrical resistivity, and magnetic properties of Fe-rich Sm(Co0.66-xSixFe0.25Cu0.065Zr0.025)7.8 magnets

The effect of Si substitution for Co on the microstructure, electrical resistivity, and magnetic properties were systematically investigated in the Fe-rich Sm(Co_0.66-xSi_xFe_0.25Cu_0.065Zr_0.025)_7.8 (x = 0–0.04) magnets. Minor Si substitution of x  = 0.01 scarcely changes the constituent phases and microstructure in the magnets. With increasing x from 0.01 to 0.04, the Zr₆(Co,Fe,Si)₂₃ and Cu-rich impurity phases increase and the crystal grain becomes fine in the magnets gradually, accompanied by the incomplete cellular structure. Besides, the Si/Cu ratio in the cell boundary phase reaches a maximum value for the x  = 0.01 magnet. As a result, the electrical resistivity at 27℃ monotonously increases from 81.9 µΩ·cm for x  = 0 to 118.0 µΩ·cm for x  = 0.04 in the direction perpendicular to the c-axis of the magnets. The vanishing of Zr-rich lamellar phase leads to an isotropy in electrical resistivity for x  = 0.04. The similar relationship exists between electrical resistivity and Si substitution at 127℃ as well. The intrinsic coercivity of the magnets first slightly increases and then decreases with increasing Si content.