Coercivity of titanium-substituted high-temperature permanent magnets

Abstract

Abstract-The temperature dependence of the coercivity of Sm-Co based magnets is investigated by magnetization measurements and model calculations. The Zr-free titanium-substituted Sm-Co material exhibits a positive temperature coefficient of the coercivity (TCC) above room temperature, a reasonable hysteresis-loop shape, and an appreciable coercivity of 12.3 kOe at 500 C for the nominal composition Sm(Co 6 2 Cu 0 8 Ti 0 3 ). The samples were produced by heat-treating the disordered 1 : 5 alloy commonly referred to as the TbCu 7 (or 1 : 7) phase. X-ray diffraction analysis shows that, upon annealing at 1165 C, the starting material segregates into more-or-less stoichiometric 1 : 5 and 2 : 17 phases. The TCC is explained by taking into account that two-phase Sm-Co magnets are of the pinning type, that is the coercivity is realized by capturing (or repelling) domain walls at 1 : 5/2 : 17 phase boundaries. Starting from a planar-defect approach, the TCC is modeled as a function of the anisotropy constants of the involved phases. The present approach yields a fair agreement between theory and experiment, and explains the existence of a coercivity maximum in terms of the Cu concentration.Index Terms-Domain wall pinning, high-temperature permanent magnets, Sm-Co based permanent magnets, temperature dependence of coercivity.

Effect of Iron Substitution on the High-temperature Properties of Sm(Co,Cu,Ti)z Permanent Magnets

“…This is due to the different temperature dependence of the two phases (1:5 and 2:17). A detailed explanation of this mechanism has been given elsewhere [4]. Figure 3(a) shows the room-temperature loop of a sample, whereas 3(b) shows the same sample after alignment.…”

“…On further addition of Fe, the TCC becomes negative and also the coercivity drops to a relatively low level. The positive TCC has been explained by a model in terms of domain-wall-pinning mechanism in a two-phase magnet [4]. As in the case of conventional SmCo 2:17 magnets, Fe substitutes for Co and most likely enters the main 2:17 phase in the cellular structure, and also stabilizes the 2:17 phase at the presence of Cu [5].…”

“…Our previous studies have been focused on SmCo-based alloys with Ti-substitution and their possible use as high temperature permanent magnets [3,4]. An abnormal temperature dependence of coercivity has been found and an explanation for that has been given.…”

Hybrid High-Temperature Nanostructured Magnets

“…In the last couple of years efforts have been made to improve the properties of this class of material by adjusting the composition and Hc values up to 10 kOe have been obtained at 500 'C [I]. Recently we have discovered a relatively simple Sm-Co-Cu-Ti alloy that consists of two phases, 2:17 and 1:5, and which has a positive dHc/dT and H, values above 10 kOe at 500 'C [2,3]. We discuss here our most recent improvements in this material and our understanding of its behavior.…”

“…where Ho is the anisotropy field of the main (2:17) phase, Kh is the anisotropy constant of same phase, b is the thickness of the boundary (1:5) phase, 5 is the domain-wall thickness, and AK = Kh -K, where Ks is the anisotropy of the softer boundary phase [3]. By considering the expected temperature dependence of Kh and K, and the expected dependence of Ks on Cu content, it is possible to rationalize the temperature dependence of H-(T) shown in Figure 5, including the maximum in H,(T) seen for the sample with x = 0.6.…”