Why doesn't chromium show ferromagnetism?

I'm guessing you meant Manganese rather than Magnesium, since Manganese has five unpaired electrons but Magnesium doesn't. The answer is that ferromagnetism is not simply a function of having unpaired electrons. The effect is far more subtle than that. read more

It is not possible to explain the antiferromagnetism of chromium with Hund's rules - Wikipedia. You need to use the RKKY interaction - Wikipedia. The lattice constants of chromium metal are the wrong size for the interaction between spins on neighboring chromium atoms to be ferromagnetic. read more

I'm guessing you meant Manganese rather than Magnesium, since Manganese has five unpaired electrons but Magnesium doesn't. The answer is that ferromagnetism is not simply a function of having unpaired electrons. read more