Nb doping effect in VO2 studied by investigations of magnetic behavior

Abstract It is shown that for samples of V 1- x Nb x O 2 (0 ≤ x ≤ 3%), each undergoes a magnetic transition characterized by an abrupt variation in susceptibility, and the transition temperature T m , x shifts from 333.4 K to 303 K with x from 0% to 3%. Above T m , x the susceptibility weakly varies with temperature, while below T m , x it varies inversely with temperature. Based on quantitative approaches to susceptibility data, it is proposed that Nb doping not only introduces additional electrons, which leads to an enhancement of the whole in susceptibility for the whole temperature range, but also makes part of V 4+ ions become paramagnetic V 3+ ions, which results in a strong variation of susceptibility inversely with temperature below T m , x . The doping-induced decrease in T m , x is explained to be due to the increase in separation between adjacent V 4+ ions and the presence of PM V 3+ ions, both being unfavorable to the formation of dimers.