Thermal Stability and Magnetic Properties of Fe−Polyoxocation Intercalated Montmorillonite

Iron polyoxocation montmorillonite complexes were prepared by ion exchange. The thermal stabilities of the complexes were determined to 750 degrees C. Their magnetic behavior was investigated between 2 K and room temperature. The complexes were stable when heated to 500 degrees C for as long as 60 h although the magnetic behavior for that specimen differs from those heated for shorter periods. At 750 degrees C the pillared sample collapsed but could be reexpanded with additional Fe-polycation. A dried specimen of the Fe-polycation exhibits spin glass behavior. Intercalated specimens heated in the range 200-500 degrees C for 1-2 days exhibit complex magnetic behavior when susceptibilities are measured for zero-field-cooled samples. An initial asperomagnetic spin arrangement at 2 K undergoes a transition at 4.4 K to a new asperomagnetic state that then relaxes to a speromagnet. The freezing temperature is about 15 K.