Evolution of magnetic domain structures and coercivity in high-performance SmCo 2:17-type permanent magnets

The magnetic domain structure of SmCo 2:17-type magnets has been found to be very sensitive to details of the processing procedure. In optimally processed high-temperature Sm(Co0.784Fe0.100Cu0.088Zr0.028)7.19 magnets, the typical domain width is less than 1 μm, but significantly larger than the typical size of 2:17R cells of about 100 nm. However, quenching straight from the aging temperature of 850 °C, i.e. omitting slow cooling, leads to a much coarser domain structure (domain width ∼10 μm) and a small coercivity (<0.1 T). The fine domain structure of the optimally processed bulk magnet can be considered as interaction domains – an alternative phenomenon compared to the zigzag-shaped domain walls known for thinned specimens. Another, commercially available 2:17-type magnet, developed for low room temperature coercivity and high second quadrant squareness, has a much coarser domain structure, even when slowly cooled from 780 to 400 °C.