Trace Ferromagnetism in Zeolites

Broad, intense electron resonance signals have been observed in heat‐treated synthetic zeolites. Static susceptibility and high‐temperature resonance measurements prove that the signals are ferromagnetic resonances. The observed Curie temperature of about 570°C strongly suggests that, during activation, ferromagnetic Fe3O4 is formed from trace amounts of ionic impurities present in the zeolitic starting materials.