NMR Studies of VO2 and V1-xWxO2

An extensive study of the 51 V NMR in VO 2 has been made between 4.2 K and 600 K, particularly laying stress on the analysis of the temperature dependence of the nuclear relaxation rate 1/ T 1 . In the metallic (M) phase ( T > T t =340 K) an exchange-enhanced Korringa relaxation process for 1/ T 1 is observed and the spin fluctuation effects have been treated within RPA. In the insulating (I) phase ( T < T t ), 1/ T 1 ( T ) cannot be explained from a simple band model and it is proposed that the hopping motion of the self-trapped carriers or excitons are responsible for the relaxation process. The 51 V NMR in the substitutional compounds,V 1- x W x O 2 (0≤ x ≤0.075), has also been studied in the M phase in order to obtain further knowledge to the M-I transition. From the RPA analysis, it is shown that the x -dependence of the experimental data are in general accord with the nesting model proposed by M. Gupta et al .