Ferromagnetism and structural transformations caused by Cr intercalation into TiTe2

Crystal structure investigations, electrical resistivity, and magnetic measurements have been performed for polycrystalline samples of intercalated compounds CrxTiTe2 with a Cr concentration up to x = 0.65. According to the room-temperature x-ray diffraction study of CrxTiTe2, the initial hexagonal crystal structure transforms to a monoclinic one with increasing Cr content up to x >= 0.5 due to the ordering of Cr ions. The intercalation results in the change of the resistivity behavior in CrxTiTe2 from metal-like at x = 0 to insulator-like above x = 0.33 and leads to ferromagnetic ordering of Cr magnetic moments at x >= 0.5. For the compound Cr0.25TiTe2, structural transformations and anomalous resistivity behavior are observed around 230 K, which cannot be explained only by the order-disorder transition within the subsystem of intercalated Cr ions. Structural changes within Te-Ti-Te sandwiches associated with charge density wave instability are suggested to be involved in this phase transition as well.