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A comprehensive characterization of sintered magnets with composition Sm(Co bal Fe 0.06 Cu x Zr 0.03 ) z , where 0.088 x 0.128 and 5.8 z 7.2, was undertaken with the objective of clarifying the coercivity mechanisms. For the range of compositions evaluated in this study Cu has a small effect on microstructure, while z has a more pronounced effect. The abnormal coercivity behavior as function of temperature takes place preferentially in samples with low Cu and low z. The microstructure of the samples is composed by cells of rombohedral Sm 2 (Co,Fe) 17 phase, a cell boundary hexagonal Sm(Co,Cu) 5 phase and lamellae of the crystallographically coherent Zr rich platelet phase. Magnetic viscosity studies show that the activation length L a (7-20 nm) has a dimension very similar to the width of the cell boundary phase (10 nm) and is also compatible with the cell size (10-90 nm). Through the Barbier plot, it is found a law of the type S V H c 0.71 , for Sm(CoFeCuZr) z samples with coercivity between 0.09 and 4.2 T. Initial magnetization curves and the angular dependence of the coercivity are used to discuss coercivity mechanisms.

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