Magnetic multilayers of a ferromagnetic (FM)/insulator (I)/ferromagnetic (FM) structure have been studied to investigate magnetic exchange coupling between two FM layers. As the Mumetal $(Ni_{77}Fe_{14}Mo_{5}Cu_4$ wt%) growth temperature increases, the grain size and the surface roughness increase simultaneously. The smallest coupling field is obtained at $40^circ{C}$ where the grain size is larger than that of the $20^circ{C}$ sample. The exchange coupling field increases again at temperatures higher than $40^circ{C}$ due to increase in the surface roughness of the Mumetal.