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.

Lorentz microscopy combined with conventional transmission electron microscopy were used to image the magnetic domains and microstructures of sintered Sm͑Co bal Cu x Fe 0.06 Zr 0.03 ) z ͑0.088рx р0.128; 5.8рzр7.2͒ permanent magnets which were specifically designed for high temperature applications. The microstructural data were correlated with the magnetic measurements to understand the origin of coercivity. All sintered magnets showed typical cellular and lamellar microstructures. The cell size and coercivity were found to be more sensitive to z than to the Cu content. For a fixed Cu content, by increasing z from 5.8 to 7.2, the cell size was found to vary dramatically from 10 to 80 nm and the coercivity from 5.6 to 40 kOe, respectively. On the other hand, for fixed z, the cell size decreases slightly with increasing Cu content from 0.08 to 0.128 and the corresponding coercivity increases from 23.6 to 40 kOe. Both z and the Cu content show a smaller effect on the cell boundary width and lamella phase density. Domain wall pinning is observed in all magnets studied, irrespective of their cell size. The smaller the cell size, the less wavy the walls are, and the lower the coercivity. The Lorentz microscopy data indicate that the majority of pinning sites are the cell boundaries with occasional pinning at the intersection of cell boundaries with the lamella phase.

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There has been an increasing demand for high temperature soft magnetic materials with mechanical properties better than those of existing commercial materials such as FeCo alloys. We have designed new magnetic composites by reinforcing FeCo alloys with high strength tungsten fibers. The composite materials were fabricated by electrodeposition. In general, the asdeposited composites have a relatively high coercivity H, and low magnetic permeability t, because of induced strain during fabrication. After appropriate thermal annealing, the composites have good soft magnetic properties, comparable to commercial bulk alloys. However, the saturation induction is reduced due to the non-magnetic inclusions. The composites also show significant enhancements in yield strength and tensile strength that increases linearly with fiber volume fraction as seen in other common composite materials. In addition, near zero creep is observed at 600 TC under a stress of 600 Mpa. The mechanical properties can be further improved by co-depositing soft magnetic material and A1 2 0 3 onto the fibers. An approximately linear relationship was observed between the coercivity and volume fraction of A1 2 0 3 particles. The square-root relationship was observed between the hardness and the A1 2 0 3 concentration.