Size-dependent Magneto-catalytic Effect in Ferromagnetic Nanoparticles

The magneto-catalytic effect (MCE) indicates that the paramagnetic (PM) state of a ferromagnet could exhibit a distinct chemical reactivity from its ferromagnetic (FM) ground state. Recently, we have system-atically investigated the MCE on cobalt-catalyzed ammonia synthesis by ab initio spin dynamics. Howev-er, our model is still in the scope of ideal single-crystal facets rather than realistic nanoparticles (NPs). In this work, we employ an atomistic model using a nearest-neighbor Heisenberg Hamiltonian exchange to computationally study the size dependence of the MCE at nanoscale particles. As a result, the optimal reac-tion temperature for cobalt NPs to achieve the Sabatier optimal activity for ammonia synthesis can be de-creased by 300 K at an adequate particle size compared with that derived from bulk. We believe our find-ings could bridge the gap between the properties of bulk phase transition and the localized chemical reac-tions at heterogeneous interfaces.