Observation of Magnetic and Structural Phase Transition in CsFeS₂

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Both neutron diffraction and Mössbauer investigation reveal that CsFeS₂ remains paramagnetic down to 70 K, at which a sudden first order magnetic and structural phase transition takes place. Antiferromagnetic coupling of spins both along the c-axis and along the diagonal direction in the a-b plane of the orthorhombic crystal structure of the high temperature phase accounts best for the observed low temperature neutron diffraction data. Mössbauer parameters determined over the temperature range from 4.2 K to room temperature indicate that the iron in CsFeS₂ is in a ferric state having large covalent bonding to sulfur ligands. The measured hyperfine field of 193.0±0.1 kOe at 4.2 K is a quite reduced value compared with those of other high spin ferric compounds.