Mössbauer Study on the Magnetism of Trinuclear Complex Salts

A susceptibility measurement on [Fe 3 O(CH 3 COO) 6 (H 2 O) 3 ]Cl·6H 2 O at temperatures between 4.2 K and 1.3 K shows that the triangular Fe 3+ -clusters have spin 1/2 in the ground state owing to strong antiferromagnetic intracluster interactions. The Mössbauer spectrum of this salt in the external field of 50 kOe at 1.5 K consists of three sets of magnetically split patterns with the effective fields of 210 kOe, 175 kOe and 80 kOe, respectively. The spectrum from the (Cr 2 Fe)-clusters in the isomorphous Cr-salt with Fe 57 substituting for Cr 3+ ions up to 2% has a single pattern with the effective field of 235 kOe. It is shown that antiferromagnetic intracluster interactions cause the constituent Fe 3+ (and Cr 3+ ) ions to have small positive or negative spin components along the large polarizing field. The three interactions in an Fe-cluster are not equivalent to each other. For a (Cr 2 Fe)-cluster, the Fe 3+ -Cr 3+ interactions are stronger than the Cr 3+ -Cr 3+ one.