Morphology evolution of SmCo_x permanent magnetic nanoparticles

Sm-Co nanoparticles (NPs) are promising candidates for preparing superstable magnets and exchange-coupled nanocomposite magnets with unprecedented magnetic properties. However, the morphology evolution of the NPs remains unclear. Here, single crystalline SmCo_x (x = 4.07, 4.79, 6.94, and 8.61) NPs with dimensions below the critical size of a single magnetic domain were synthesized. These NPs consist of Sm₂Co₇, SmCo₅, and Sm₂Co₁₇ phases with divergent typical morphologies. An evolution model for the different morphological characteristics was proposed based on phase-structure changes and surface-energy calculations using the density functional theory. The results show that these SmCo_4.79 NPs can be well aligned along the easy magnetization axis and exhibit an ultrahigh coercivity of 5.7 T, thus enabling to advance the control of NP morphology and to facilitate their use in superstable or nanocomposite magnets.