Structural and magnetic properties of self-assembled Sm–Co spherical aggregates

Self-assembled Sm–Co nanoparticles in the form of spherical aggregates (referred as nanospheres) with diameter ranging from 50 to 180 nm were achieved by means of polyol technique. The size distribution of the Sm–Co nanospheres can be regulated close to ∼100 nm by controlling the molar ratio of Sm:Co precursor. The spherical aggregates exhibited Sm2Co7 phase as a major constituent; while the aggregates obtained at higher Co concentration showed co-existence of Co-phase with Sm2Co7 phase. Upon annealing, the biphasic nature of nanospheres (Sm2Co7/Co) transformed into Sm2Co17 structure. By varying the Sm:Co precursor ratio from 1:5 to 1:9, the coercivity (Hc) and magnetization (Ms) values of the as-synthesized nanospheres can be tuned from 336 to 140 Oe and from 63.7 to 108 emu/g, respectively, and these values significantly improved after annealing. Maximum values of Hc (1050 Oe) at the Sm:Co molar ratio of 1:5 and Ms of 184.6 emu/g at the Sm:Co molar ratio of 1:9 were achieved in the annealed samples.

► Self-assembled Sm–Co nanoparticles in the form of nanospheres were succeeded.
► Both monodispersity and phase composition are dependent on the Sm:Co molar ratio.
► Upon annealing, phase transformation of Sm2Co7/Co into Sm2Co17 occurred in the nanospheres.
► Hc and Ms values of nanospheres can be tuned by varying the Sm:Co ratio from 1:5 to 1:9.