Abstract
Resistivity, Hall voltage, magnetic susceptibility and Mössbauer parameters of Fe0·25NbS2 and Fe0·33NbS2 have been measured on powders and on single crystals as a function of the temperature, from 4·2 to 300 K. The structures of both compounds are related to the NbS2–2s type (hexagonal cell a, c) with the Fe ions forming an ordered superlattice (2a, c in Fe0.25NbS2 and a √ 3, c in Fe0.33NbS2). Magnetic susceptibility and Mössbauer experiments show that these compounds are antiferromagnetically ordered respectively at 137 and 47 K; the magnetic moments in the antiferromagnetic state are parallel to the c axis. Two anomalies are observed in the transport properties of Fe0.25NbS2, evidenced by an increase of the resistivity when the temperature decreases and by a change of the sign of the Hall coefficient. A metallic behaviour is observed in both compounds. The comparative Mössbauer study shows that the ionic Fe2+ behaviour is more pronounced in Fe0·33NbS2 than in Fe0·25NbS2.