Magnetic and Charge Dynamics in a Doped One-Dimensional Transition Metal Oxide

Abstract

We have measured the electrical resistivity, polarized x-ray absorption, and magnetic neutron scattering for ${\mathrm{Y}}_{2\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Ba}{\mathrm{Ni}}_{1\ensuremath{-}y}{\mathrm{Zn}}_{y}{\mathrm{O}}_{5}$ to determine how doping affects the charge and spin dynamics of a Haldane chain compound. While Zn doping, which severs the NiO chains, increases the resistivity beyond that of the pure material, Ca doping introduces holes, residing mainly in the ${2p}_{z}$, orbital of the oxygens in the NiO chains. Both dopants lead to simple finite size effects above the Haldane gap. In addition, we have discovered that Ca doping yields substantial magnetic states below the Haldane gap.