PHASE-TRANSITION AND ELECTRON LOCALIZATION IN 1T-TAS2

The magnetic properties and phase transitions of 1T-TaS2 and 1T-Fe0.07 Ta0.93S2 have been studied in the interval of 1.5-300 K and over the r ange of 100 Oe-60 kOe. Experimental results show that at high temperat ures the compounds are in a diamagnetic state and the -charge-density- wave-triclinic-nearly-commensurate transition temperature of 1T-TaS2 d ecreases with increasing magnetic field. The amount of variation is a function of the magnetic held. At low temperatures both 1T-TaS2 and 1T -Fe0.07Ta0.93S2 are in a paramagnetic state owing to the localized mom ents that come from the single Anderson-Mott localization state. The c urves of magnetization versus temperature do not follow the Curie law or Curie-Weiss law, but can be described fairly well as M = M(0) + gam ma T--n. The fitting parameters of experimental curves show that a par t of the neighboring moment appears as antiferromagnetic coupling due to exchange interaction between the moments. The magnetic-field depend ence of magnetization exhibits a complicated feature at low temperatur e. It shows that the compounds may undergo a phase transition at the m aximum value of magnetization and then they are probably in a mixed ch arge-density-wave-spin-density-wave (CDW-SDW) state or SDW state due t o the coherent superposition of the antiferromagnetic coupling.