Hopping conductivity in one-dimensional Ca/sub 3/Co/sub 2/O/sub 6/ single crystals

Abstract

We studied the electronic conductivity and magnetic properties of quasi-one-dimensional Ca₃Co₂O₆ single crystals. The results evidence a variable range hopping conductivity with temperature-induced crossover between one-dimensional (intrachain) and three-dimensional (3D) transport and the opening of a Coulomb gap in the d bands along with the ferromagnetic intrachain ordering. At low temperatures, an applied magnetic field induces a large negative magnetoresistance (MR) in apparent dissociation with the 3D magnetic ordering. Both spin-dependent hopping and field-induced suppression of the Coulomb gap are discussed. The electronic hopping parameters we infer agree remarkably with the accessible Co sites. Surprising narrow peaks corresponding to a transient resistivity decrease are observed on the MR curves. We discuss these in terms of peculiar in-plane magnetization states in an Ising-like Heisenberg antiferromagnetic triangular lattice during the magnetization reversal.