Negative Colossal Magnetoresistance Driven by Carrier Type in the Ferromagnetic Mott Insulator GaV₄S₈

Abstract

We report here a study on the evolution of structural and electronic properties of the lacunar spinel compounds GaV 4 S 8 with charge doping. In this ferromagnetic (FM) Mott insulator, the heterovalent substitutions of Ga 3+ by Zn 2+ or Ge 4+ allow induction of charge doping either by holes or by electrons. We show that electron-doped GaV 4 S 8 displays a bulk, negative, and colossal magnetoresistance (CMR) with a relative drop of resistivity reaching −80% at 7 T in the vicinity of the Curie temperature. Conversely, hole-doped GaV 4 S 8 does not display any negative CMR but a classical positive magnetoresistance. This asymmetric electron–hole doping effect challenges the common view stating that CMR effects in doped FM Mott insulators depends only on the density of carrier and not on their electron/hole nature. We show that a simple model based on multiorbital effects and Hund’s rule is able to capture the presence (absence) of negative CMR in electron- (hole-) doped GaV 4 S 8 .