[pawelkkk1]

Do you know any chemical reaction after which magnetic properties of compound change?

[Rabn]

reduction or oxidation of iron would change the magnetic properties of the compund. i.e oxidation of Fe_(s) to Fe₂O₃.  If I remember correctly the magnetic ability of iron is reflective of its half full d shell electrons' spins in alignment.

[pawelkkk1]

Wow, that was fast! I posted it 5 mins ago

And would it be possible to exhange oxygen with calcium? Im looking for compounds to selectively react with calcium and become magnetic.

Thanks you for reply.

[Rabn]

How much chemistry do you know? Curious after that last question.  You could probably reduce the iron oxide back to solid iron. You would have to check a reduction table.

[pawelkkk1]

Im after studies in physics and there is not much overlap usally between those subjects at university. So I have bit problem with formulating my question.

I'm trying to find some form (liquid preferably) of calcium detector. That is, if there is calcium around - it becomes magnetic.

 

[Rabn]

Calcium specific detectors are available in a form very similar to an electronic pH measuring device. http://www.vernier.com/probes/ca-bta.html is an example.