Formation of a Sm-Co alloy film is carried out by means of wet plating system which is easily practicable and well suited for treatment intricate and/or large configurations. The system uses a plating bath which contains chlorides of samarium and cobalt dissolved with non-aqueous solvent such as formamide. Substantial absence of any aqueous components in the plating bath assures production of a plated film of high purity and quality. Content of samarium in the product can feeely be adjusted by choice of the current density of direct current to be employed in the electrolytic plating.