I have an odd coin with legends ADELIE REGIES from 2007 and denominated as 25 Francs that features two penguins under a crown and is said to be made of hafnium, for French Antarctica, Adelie Land. They do exist. Minor legends include FRZ "fec(it) and T.A. Essai. It has three stylized fleur di lis' and an anchor in a square design.
They are, like all other "Antarctic coins", unoffical, privately-made coin-like medals; "fantasy coins", to use the proper classification.
The website says they're made of nickel, no mention of a halfnium version. Given that halfnium's only commercial use is in nuclear power plants, I don't think halfnium coins would be legal to make or own or be unregulated. Depending on your jurisdiction, you'd need a permit to own one.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis