Magnetic hardening studies in sintered Sm(Co,Cu-x,Fe,Zr)(z) 2 : 17 high temperature magnets

Lorentz microscopy combined with conventional transmission electron microsc opy were used to image the magnetic domains and microstructures of sintered Sm(CobalCuxFe0.06Zr0.03)(z) (0.088 less than or equal to x less than or eq ual to 0.128; 5.8 less than or equal to z less than or equal to 7.2) perman ent magnets which were specifically designed for high temperature applicati ons. The microstructural data were correlated with the magnetic measurement s to understand the origin of coercivity. All sintered magnets showed typic al 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 con tent, by increasing z from 5.8 to 7.2, the cell size was found to vary dram atically from 10 to 80 nm and the coercivity from 5.6 to 40 kOe, respective ly. On the other hand, for fixed z, the cell size decreases slightly with i ncreasing Cu content from 0.08 to 0.128 and the corresponding coercivity in creases from 23.6 to 40 kOe. Both z and the Cu content show a smaller effec t on the cell boundary width and lamella phase density. Domain wall pinning is observed in all magnets studied, irrespective of their cell size. The s maller the cell size, the less wavy the walls are, and the lower the coerci vity. The Lorentz microscopy data indicate that the majority of pinning sit es are the cell boundaries with occasional pinning at the intersection of c ell boundaries with the lamella phase. (C) 2000 American Institute of Physi cs. [S0021-8979(00)29208-6].