A granular system of FeRh-based nanoprecipitates (similar to 10-15 nm diameter) embedded in a rapidly solidified copper ribbon matrix was found to transit from a metastable tetragonal L1(0) (AuCu-1-type) structure to a stable B2 (CsCl-type) structure upon annealing-induced coarsening to similar to 94 nm. The hysteretic magnetic transition observed at similar to 100 K develops a gradual broadening that accompanies the L1(0) -> B2 crystal structure transition. It is proposed that the Cu matrix influences the structural and magnetic properties of the FeRh-based nanoparticles through interfacial strain and chemical effects. These results emphasize the sensitivity of the magnetostructural response of FeRh to changes in the nanostructural scale, and provide pathways for tailoring the transition. (C) 2013 AIP Publishing LLC.