Magnetic hardening studies in sintered Sm„Co,Cux ,Fe,Zr...z 2:17 high temperature magnets

Lorentz microscopy combined with conventional transmission electron microscopy were used to image the magnetic domains and microstructures of sintered Sm~CobalCuxFe0.06Zr0.03)z ~0.088<x <0.128; 5.8<z<7.2! 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. © 2000 American Institute of Physics. @S0021-8979~00!29208-6#