Intercalation of n-alkylamines in FePS₃

Abstract

The intercalation of linear alkylamines (C₁-C₄) in the two-dimensional (2D) Ising antiferromagnet, FePS₃, has been investigated. Intercalation proceeds with a dilation of the interlayer distance. The expansion (~3.8 Å) is the same for all four amine molecules, suggesting that they are oriented flat with respect to the layers. From an analysis of the products of deintercalation, it is concluded that the intercalated species are the alkylammonium cations and neutral amine molecules. The intercalated compounds are highly moisture sensitive, as reflected in the chemical nature of the intercalated species. Charge neutrality of the lattice after intercalation is preserved by the loss of Fe²⁺ ions from the lattice. These Fe²⁺ ions are further oxidized to form superparamagnetic Fe₂O₃ clusters, as confirmed by Mossbauer spectra and magnetic measurements. This was further corroborated by in situ EPR studies. The ⁵⁷Fe Mossbauer spectra of the intercalated compounds showed evidence for two species other than Fe₂O₃. On the basis of the observed isomer shifts and quadrupole splittings, they have been assigned to Fe²⁺ in an environment similar to that in FePS₃ and in a distorted FePS₃ environment. The temperature and field dependence of the magnetic susceptibility of single crystals of the amine-intercalated FePS₃ have been measured. Their magnetic behavior shows many of the features expected of a 2D Ising antiferromagnet with random defects, Fe_1-xPS₃, in agreement with the mechanism of intercalation.