Effect of magnetic fields on the metal-insulator transition in BaVS3

We report measurements of the high field magnetoresistance of single crysta ls, and of the low field Hall effect and high field magnetization of polycr ystalline samples of BaVS3. Below the temperature T(MI)similar or equal to 70 K of the metal-insulator (MI) transition, the magnetization is linear fo r 0<H<45 T. The magnetoresistance varies as a(T)H-2 for 0<H<18 T, and a(T) varies proportionally to the logarithmic derivative of the zero field resis tivity (1/rho)d rho/dT. This result allows us to estimate the zero temperat ure critical field H(0)similar or equal to 260 T (=175 K); for this value, the spin gap is substantially smaller than the charge gap given by Delta(c) similar or equal to 500 K. The Hall constant increases to very large positi ve values for T<T-MI, and shows considerable precursive activity for T>T-MI indicative of fluctuations in the gap above the MI transition. We use thes e results to discuss several models for the MI transition. [S0163-1829(99)0 1942-6].