Influence of the type of surfactant and hot compaction on the magnetic properties of SmCo₅ nanoflakes

In this study, we discuss the effects of a type of surfactant (oleylamine, oleic acid, and trioctylamine) and hot pressing on the hard magnetic properties of crystallographically anisotropic SmCo₅ nanoflakes prepared by surfactant-assisted high energy ball milling. The phase, microstructure, and magnetic properties of the hot-pressed SmCo₅ were investigated by using x-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The coercivities of the precursor flakes prepared using oleylamine, oleic acid, and trioctylamine were 14.9, 15.8, and 15 kOe, respectively. Hot-compacted SmCo₅ magnets prepared from the nanoflakes milled with oleic acid had the lowest coercivity of 8.1 kOe. It is believed that even after repeated washing in an ultrasonic bath with different solvents, the remaining oleic acid in the SmCo₅ nanoflakes led to oxidation of SmCo₅ at the surface/interface of nanoflakes during the hot-pressing process. The compacted SmCo₅ magnets prepared from the nanoflakes milled with trioctylamine and oleylamine had higher coercivity values of 14.8 and 12.8 kOe, respectively. Unlike oleic acid, oleylamine and trioctylamine contain no oxygen atoms, and therefore there was less oxidation during the process. The compaction temperature also influences the coercivity. The SmCo₅ magnets hot pressed at 550 °C had the highest coercivity, whereas those hot pressed at 650 °C had the lowest coercivity; this is attributed to the change of phases and composition of SmCo₅ alloys during the hot-pressing process.