Many Neodymium magnets are coated in Nickel, Copper, and Nickel again. Titanium Nitride is a popular coating used as a biocompatible outer layer. It usually has a gold coloring.
One layer of biocompatible coating isn’t really enough. Microscopic imperfections in the coating allow your body to get at the interior of the magnet and over a few years the magnet falls apart.