Samarium Cobalt (SmCo) magnets contain less free iron than Neodymium magnets and therefore provide better corrosion resistance than Neodymium magnets. It is very rare for SmCo magnets to require protective plating (a notable exception is the use of nickel plating for soldering the magnets to printed circuit boards). Sm1Co5 contains no iron so has excellent corrosion resistance. Sm2Co17 has some free iron that may corrode on the magnet surface when exposed directly to water. Sm2Co17 is still, for most applications (other than marineenvironments) regarded as having good to very good corrosion resistance (in marine applications the magnet can be given a simple low cost protective coating such as NiCuNi to prevent any corrosion possibilities) and the corrosion resistance is still far superior compared to NdFeB.

Magnetic Characteristics of Sintered SmCo: