Preparation and Magnetic Properties of Sub-Micrometer Sized Sm-Co Powders Prepared From Nanostructured Precursor Oxides

Submicrometer-sized Sm-Co powders have been prepared by the calciothermic reduction and subsequent solid-state diffusion of a nanostructured Sm-Co-O/Co-O precursor. The Sm and Co containing precursor was prepared by an autocombustion process. X-ray diffraction identified the product as a mixture of SmCoO
₃
and Co
₄
O
₄
. This powder was mixed in a 1:2 mass ratio with CaO (which served as a thermal ballast and aggregation inhibitor) and milled to reduce the particle size below 1 micrometer. Ca metal was added to the mixed powder in amounts between 2 and 6 times those required to reduce the Sm and Co oxides, and sealed in Nb tubes for heat treatment at 900°C for various lengths of time. After cooling to room temperature, metallic Sm-Co particles were isolated from the undesired reaction products by a series of washing steps in acetic acid and ethyl alcohol. The Sm-Co particles were characterized by scanning electron microscopy, vibrating sample magnetometry, and X-ray diffraction. These measurements demonstrated that smaller particle sizes were associated with shorter reaction times and smaller quantities of reducing agent. The formation of hard SmCo
₅
was systematically associated with either long diffusion times with small amounts of reducing agent, or short diffusion times with large amounts of reducing agent.