Phase transition and electron localization in 1T-TaS2

The magnetic properties and phase transitions of 1T-${\mathrm{TaS}}_2$ and 1T-${\mathrm{Fe}}_{0.07}$ ${\mathrm{Ta}}_{0.93}$ ${\mathrm{S}}_2$ have been studied in the interval of 1.5–300 K and over the range of 100 Oe–60 kOe. Experimental results show that at high temperatures the compounds are in a diamagnetic state and the commensurate-charge-density-wave–triclinic-nearly-commensurate transition temperature of 1T-${\mathrm{TaS}}_2$ decreases with increasing magnetic field. The amount of variation is a function of the magnetic field. At low temperatures both 1T-${\mathrm{TaS}}_2$ and 1T-${\mathrm{Fe}}_{0.07}$ ${\mathrm{Ta}}_{0.93}$ ${\mathrm{S}}_2$ are in a paramagnetic state owing to the localized moments that come from the single Anderson-Mott localization state. The curves of magnetization versus temperature do not follow the Curie law or Curie-Weiss law, but can be described fairly well as M=${\mathit{M}}_0$+γ${\mathit{T}}^{\mathrm{-}\mathit{n}}$. The fitting parameters of experimental curves show that a part of the neighboring moment appears as antiferromagnetic coupling due to exchange interaction between the moments. The magnetic-field dependence of magnetization exhibits a complicated feature at low temperature. It shows that the compounds may undergo a phase transition at the maximum value of magnetization and then they are probably in a mixed charge-density-wave–spin-density-wave (CDW-SDW) state or SDW state due to the coherent superposition of the antiferromagnetic coupling.