Microstructures and magnetic properties of size-controlled Sm-Co nanoparticles synthesized via calcined precursors and reduction-diffusion (RD) process

Abstract

To optimize the magnetic properties of Sm-Co nanoparticles, precise control of the size and phase composition is crucial. Sm-Co-O/CaO composites have conventionally been prepared using the reduction-diffusion (RD) process and sintering to suppress particle growth. However, this diffusion-controlled redox reaction occurs through the CaO layer, and variations in the thickness or density of the CaO layer can lead to irregular Sm-Co particle size distribution. Incomplete reduction may also result in the formation of residual oxide phases. To avoid these issues, this study introduces a calcination process to prepare precursors optimized for the RD process. To achieve a uniform CaO layer during calcination, Sm-Co-O particles synthesized via the solvothermal method were wet-coated with Ca(ac)(2)<middle dot>H2O. The final precursor structure was controlled by analyzing the thermal decomposition and phase transition behavior throughout the calcination process. The synthesized precursor was converted into Sm-Co powder through the RD process. As a result, particle growth was effectively suppressed, and Sm2Co17 particles with an average size of 145 nm, were successfully synthesized at 800 degrees C, which is below the melting point of Ca. Furthermore, by controlling the precursor composition, a mixed phase consisting of Sm2Co17 and SmCo5 was successfully synthesized, achieving a (BH)max calculated from the density of the mixed powder of 21.9 MGOe at an applied magnetic field of 25 kOe.