High temperature electrical resistivity measurements of sintered samarium Cobalt magnets

• Anisotropic resistivity observed in both 1:5 and 2:17-type SmCo sintered magnets. • Increased Zr content lowered resistivity perpendicular to c-axis for 2:17-type. • Resistivity change up to 200 °C found to be linear for all orientations. • When magnetised, resistivity at 200 °C observed to be lower than non-magnetised. When modelling permanent magnet motors, it is important to understand the resistivity of the magnetic material, and its eddy current flow. These motors often operate over a wide range of temperatures and thus an understanding of the temperature dependency of resistivity is necessary for accurate modelling. For SmCo type magnets it has been shown that electrical resistivity can be anisotropic for 1:5 and 2:17-type magnets, and that operating temperature can significantly change resistivity. The authors investigated the temperature dependence of different commercial grade SmCo 2:17-type and 1:5-type magnets, up to 200 °C, in both a magnetised and non-magnetised condition. Anisotropic resistivity was observed in both types, with the 2:17-types having lower resistivity in the plane perpendicular to the c-axis, and the 1:5-type having lower resistivity in the parallel plane. At room temperature, resistivity was found to be similar in both the magnetised and non-magnetised states and a linear increase in resistivity was observed with increasing temperature for both. However, the temperature coefficient was found to be lower in the magnetised state, leading to a lower resistivity at higher temperatures than for the non-magnetised state. For 2:17-type magnets of similar composition, differences in the Zr content and the Zr-rich lamellae within the cellular structures were found to produce variations in the resistivity, only in the axis perpendicular to the c-axis. An additional 0.31 wt% of Zr is shown to lower resistivity by 0.7%.