• (a.) Acting by the agency of heat and magnetism; as, a pyromagnetic machine for producing electric currents.
when you can change magnetic properties of a compound through heating
Pyr`o·mag·net'ic adjective [ Pyro- + magnetic .] (Physics) Acting by the agency of heat and magnetism; as, a pyromagnetic machine for producing electric currents. 
(formerly) thermomagnetic (def. 1).