The Effect of Reduction Process Parameters on Magnetic and Structural Properties of SmCo/Co Nanocomposites

Abstract

SmCo nanoplates were synthesized by a combination of Pechini type sol-gel method and reduction-diffusion process. The synthesis process started with (i) preparation of Sm-Co citrate gel, (ii) followed by annealing to obtain Sm-Co oxide powder and (iii) reduction of the powder by CaH2 at different temperatures of 870, 890, 910, 930, 950, and 970 °C for 3 h under hydrogen flow and (iv) separation of the magnetic nanoparticles through a multi-step washing process. A range of characterization techniques including XRD, TG-DTA, FE-SEM, and VSM were employed to investigate the effect of reduction temperature in terms of phase, morphology, microstructure, and magnetic properties of products. The results showed that the SmCo/Co nanocomposites were synthesized at all reduction temperatures of 870–970 °C, but by temperature increase from 930 to 950 °C, the dominant phase turned into SmCo5; the superior phase was Sm2Co17 before this step. The TG/DTA analysis indicated that at reduction temperature of 950 °C and higher, the Sm2Co17 phase is formed at the beginning, then releasing more Sm atoms results in the phase transformation to SmCo5. Meanwhile, after the temperature of 930 °C, the particle’s morphology was also changed from the nanoplates and turned into lumps. Reduced particles at 910 °C, had a maximum coercivity of 881 Oe, and the highest amount of remanence ratio (78%). However, in this sample, in spite of the presence of cobalt, as the soft phase along with SmCo, the magnetic hysteresis loop behaved like a single-phase and it proposed the hard-soft exchange coupling interaction. SmCo/Co nanocomposites were synthesized via Pechini type sol-gel method followed by reduction-diffusion process. By increasing the temperature, the dominant phase changes to SmCo5 due to the formation of excessive amount of Sm atoms. By raising reduction temperature from 930 to 950 °C, the morphology of particles changed from nanoplates to lumps. Magnetic single phase behavior as well as high remanence ratio of samples proposed the existence of exchange coupling interaction between hard and soft phases of SmCo/Co nanocomposites.