Relationship between microstructure and magnetic properties in high- energy permanent magnets characterized by polytwinned structures. Final report

摘要

This research program was initially conceived to investigate the structure-property relationships in a unique family of permanent magnet alloys which exhibit a polysynthetically twinned microstructure and high magnetocrystalline anisotropies. The polytwinned structures derive from the A1 (cubic) (r-arrow) L1(sub 0) (tetragonal) atomic ordering wherein the strain energy attendant to the transformation is relaxed by the formation of twin-related lamellae through mutual arrangement of crystallographic variants of the c-axis. This behavior is characteristic of the Co-Pt. Fe-Pt and Fe-Pd alloy systems in the vicinity of the equiatomic composition which exhibit a high, uniaxial crystal anisotropy (K(sub 1) (approximately) 10(sup 7)--10(sup 8) ergs/cm(sup 3)) with an easy c- axis. The twinned microstructure results in a magnetically modulated state since the easy axis of magnetization varies quasi-periodically on a scale (approx) 10 to 100 nm. The transformation twins are conjugated along the (l-brace)110(r-brace) planes of the fcc parent phase. In this research program, the microstructural and magnetic studies have focused on the FePd polytwinned ferromagnets. In the latter stages of the program, the work on the L1(sub 0) FePd alloys was extended to investigated of the relationship between the structure and properties of nanostructured FePd ferromagnets, as well as preliminary studies of the deformation behavior of the L1(sub 0) FePd intermetallic phase.