The electronic and magnetic properties of the 3d transition metal intercalates of TiS2

The introduction of 3d transition metals (M) into the van der Waals gaps between the weakly coupled layers of transition metal dichalcogenides TX₂ (T:transition metal, X:chalcogen) produces an interesting family of intercalation compounds, M _x TX₂, the physical properties of which are different from those of the host TX₂ matrix because of ‘host-guest’ interactions. In this article we shall review the salient features of the M _x TiS₂ family with the simple 1T-CdI₂ type layered structure, which have been extensively studied by structural, transport, specific heat and lattice dynamic, magnetic and photoemission spectroscopic measurements. In contrast with the previously reported series of intercalation complexes of the Group V transition metal dichalcogenides, a characteristic of the M _x TiS₂ materials is strong hybridisation between the guest atom M 3d orbitals and the host Ti 3d and S 3p orbitals, leading to changes in the Fermi energy E _F of the conduction band, the density of states at E _F and various types of magnetic orderings. These properties are understood in terms of an itinerant electron or band picture for the intercalant, rather than a rigid band or localised model.