Morphology evolution of SmCox permanent magnetic nanoparticles

Abstract

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 SmCox (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 SmCo4.79 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.