A granular longitudinal or perpendicular magnetic recording medium with enhanced corrosion resistance comprises: (a) a non-magnetic substrate having a surface; (b) a layer stack on the substrate surface, including a granular longitudinal or perpendicular magnetic recording layer having a surface distal the substrate surface treated to provide at least one of: (i) a reduction of nano-scale roughness and porosity; (ii) increased compositional homogeneity; (iii) increased microstructural homogeneity; (iv) preferential removal of at least one element; and (v) increased grain boundary coverage by the subsequently deposited protective overcoat layer; and (c) a protective overcoat layer on the treated surface of the granular magnetic recording layer.