Sintered ${\hbox {Sm}}_{2}{\hbox {Co}}_{17}$-Based Magnets With Small Additions of Indium

Abstract

In an attempt to develop anisotropic high-temperature permanent magnets consisting of Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Co,Fe) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> grains separated by thin layers of a nonmagnetic phase, small amounts of Ag, C, Ga, In, and Sn were added to the Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> -based alloys and sintered magnets. Grain-boundary phase(s) with the melting temperature of 985-1070 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C was obtained by adding 0.5-1.5 at. % In to Sm-Co, Sm-Co-Fe, and Sm-Co-Mn alloys with the Sm content slightly enriched compared to the 2 : 17 stoichiometry. Iron, manganese and, apparently, oxygen tend to decrease the melting temperature of the grain-boundary phase(s). Due to this low-melting-temperature phase, sintering of the milled Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> -based alloys becomes possible at temperatures as low as 1025-1075 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C. This phase is also believed to be responsible for the coercivity of 6-8 kOe observed in the Sm-Co-Fe-Mn-In alloys. The coercivity was found to be critically sensitive to the postsintering heat treatment: it dramatically deteriorates when the magnets are annealed below the melting temperature of the grain boundary phase(s).