Ultrasmall and monodisperse colloidal amorphous Nd–Fe–B–Na magnetic nanoparticles with high TC

Abstract

Ultrasmall and monodisperse air-stable colloidal Nd–Fe–B–Na nanoparticles (NPs) have been synthesized by the solution phase colloidal method and characterized by TEM, EXAFS, Mössbauer spectroscopy, and SQUID. Their size can be controlled in the sub-5 nm regime. The critical temperature (T_C) of Nd–Fe–B–Na nanoparticles with 3 nm diameter is surprisingly high, higher than 650 K. EXAFS gives the chemical environmental information of the Fe center, and Mössbauer spectroscopy confirms that the 3 nm Nd–Fe–B–Na nanoparticles contain the Fe nanocluster. A possible magnetic coupling mechanism is proposed.