Empirically, the rather low-nickel alloy (it's 70-75% copper, as I recall, you can look it up, I'm not bothering right now) that US nickels (currency, coin) are made from ignores a nice strong hard-drive magnet...
It may depend on crystal structure, as does steel (most back-yard heat treaters are aware of steel going non-magnetic as a good temperature indicator of when it might be hot enough to quench, at least if it's plain carbon steel.)