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

Abstract

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.

Magnetic domain structure in SmCo 2 : 17 permanent magnets

“…For most magnets, the coercivity is related to domain wall nucleation and propagation. While the domain nucleation mechanism is predominant in most rare-earth permanent bulk magnets like Nd-Fe-B magnets, it is generally agreed that coercivity of the Sm Co -based magnets is controlled by domain wall pinning [3]- [6]. Studies have shown that the SmCo -type cell boundaries act as domain wall pinning sites in Sm Co -based permanent magnets.…”

Magnetic microstructures of phase-separated Sm–Co 2:17-type sintered magnets

“…Although there have been numerous publications on Sm-Co 2:17-type magnets, only few magnetic domain characterizations on Sm-Co 2:17-type sintered magnets [13][14][15] have been reported. Zhang et al [13,14] studied the domain structure of the precipitation hardened 2:17-type Sm-Co magnets using Lorentz microscopy, revealing the pinning effect of domain walls.…”

“…Zhang et al [13,14] studied the domain structure of the precipitation hardened 2:17-type Sm-Co magnets using Lorentz microscopy, revealing the pinning effect of domain walls. It should be noted, however, that domain observation by TEM has only limited relevance concerning the domain structures of bulk materials and the change of those structures in a magnetization process because domain structures are very sensitive to the sample thickness.…”

Behavior of residual carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets

“…Sm(Co, Fe, Cu, Zr) z permanent magnets have excellent intrinsic magnetic properties such as very high Curie temperature (≥800 • C), high anisotropy fields (≥100 kOe) and relatively high saturation magnetizations (≥100 emu/g) [1,2]. Recently Sm(Co, Fe, Cu, Zr) z magnets have attracted considerable interest for high-temperature applications because of their large energy products and high-temperature performances [3,4].…”