Chemical composition and coercivity of SmCo5 magnets

Abstract

The effects of alloy composition and heat treatment on the intrinsic coercivity Hci of SmCo5 magnets were studied. Alloys having six chemical compositions near that of stoichiometric SmCo5 were used to produce magnets via the usual powder metallurgy techniques. Magnets were either as sintered (1150 °C) or sintered (1150 °C) and treated at 850 °C. The substantial increase in Hci due to the 850 °C heat treatment occurs reversibly and with a negligible change in lattice parameters, Curie temperature Tc and anisotropy field HA. Quantitative metallography and thermomagnetic measurements showed that the microstructural constituent present in addition to the SmCo5 phase in hyperstoichiometric alloys is composed of both the Sm2Co7 phase and the Sm5Co19 phase. Measurements of magnetization in dc magnetic fields up to 33 T suggest that HA is around 53 T, considerably higher than previously reported values. The coercivity of the magnets is discussed in terms of thermal equilibrium populations of lattice defects.

Effect of Sm content on energy product of rapidly quenched and oriented SmCo5 ribbons

“…Therefore, the V of SmCo 5 continuously expands with the increase in Sm content, which verifies the existence of the high-temperature homogeneity range for SmCo 5 . A similar tendency of change of lattice parameters with the variation of Sm content was observed in sintered SmCo 5 magnets [16,17]. and Figure 3c summarizes the deduced magnetic properties.…”

Kinetical analysis of the heat treatment procedure in SmCo5 and other rare-earth transition-metal sintered magnets

“…It has been suggested that the removal of lattice defects can be the responsible for the large increase of coercivity between sintering and heat treatment temperatures [2,3]. Even with a detailed verification of microstructure, before and after the post-sintering heat treatment in SmCo 5 [3,4,23] and NdFeB [4] magnets, no significant difference was found in microstructure, supporting the idea that the elimination of defects in atomic level can be the reason of the beneficial effect of heat treatment.…”

“…Previous microstructural studies [3,4,23] indicated that a possible microstructural change-between sintering and heat-treatment temperatures-is the elimination of rare-earth atoms from a supersatured matrix. The calculation presented in this study will take into account the experimentally measured diffusion coefficients of Sm into SmCo 5 phase [24][25][26] and the Sm-Co phase diagram [27].…”

“…This effect is observed for all main types of rare-earth transitionmetal magnets like SmCo 5 [1][2][3][4][5][6][7][8], Sm(CoCuFeZr) z [8][9][10][11][12] and NdFeB [13][14][15], but the reason of the coercivity increase remains not plentifully clarified [3,4,11].…”

Large coercivity in nanostructured rare-earth-free MnxGa films

“…The inset also shows the temperature dependence of the coercive field, H C (T), which appears to have a dependence similar to the remanence. To conclude, we note that the observed 2.5 T coercive field is on the order of those found in some important rare-earth permanent magnets, such as Nd 2 Fe 14 B where  o H C ~ 2.6 T 20 , and SmCo 5 where  o H C ~ 4 T. 21 The large coercivity of nanostructured Mn x Ga films is also present in the electronic properties through the anomalous Hall effect (AHE). The Hall effect in magnetic materials contains two main contributions, ρ H (H) = R o H + R 1 M(H,T), where R o = -1/ne is the ordinary Hall effect (OHE) coefficient, n the carrier concentration, R 1 the AHE coefficient, and M(H,T) the field and temperature-dependent magnetization.…”