The magnetic characteristics of high-anisotropy Sm(Co1−xCux)5 phases are determined experimentally at 300 K in the range x<0.6. The saturation magnetization Ms decreases and vanishes for SmCo2Cu3. Identical behaviors of Ms and Curie temperature TC versus x are observed in the range x<0.6. For significant Cu substitution rate (x≳0.35), the decrease of the anisotropy field (HA) when x increases is strong. For lower Cu contents, huge values of anisotropy fields make difficult the accurate determination of the substitution effect. The first anisotropy constant K1 is calculated using the available values of HA and Ms. A linear decrease of K1 is observed from SmCo5 to SmCo2Cu3.

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Despite the research devoted to new compounds, the Sm-Co-Cu-Fe-Zr alloys with the 2:17 type are, as yet, the only hard magnets to be used above 200 °C. However, these materials are not optimized because their coercivity mechanism is not clearly understood. Their typical microstructure consists of a network of 2:17 cells separated by 1:5 boundaries. Their coercivity is ascribed to the domain wall pinning by the 1:5 cell boundaries. The compositions of the 1:5, 2:17 phases during the cell microstructure genesis were recently evaluated for the alloy Sm(Co0.66Fe0.25Cu0.06Zr0.03)7.6. In the present work, the coercivity behavior of this alloy is analyzed from the comparison of the domain wall energies γ 1:5, γ 2:17. Sintered samples, heat-treated in various conditions, are characterized by transmission electron microscopy and hysteresis curves. γ 2:17 and γ 1:5 are calculated from measured and published data of magnetization and anisotropy. The different treatments generate similar cell microstructures but two ranges of coercivity (about 600 and 2200 K A m−1). In the two cases, γ 1:5 is larger than γ 2:17: the cell boundaries appear as repelling energy barriers rather than pinning sites. The existence of a disturbed anisotropy layer along the 1:5/2:17 interface is proposed to explain the higher coercivity state. The evaluation of Hc using the usual models is attempted.

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