Electronic properties of Sr14Cu24O41.

Abstract

Crystals of orthorhombic ${\mathrm{Sr}}_{14}$${\mathrm{Cu}}_{24}$${\mathrm{O}}_{41}$ are semiconducting, with an activation energy of 0.18(2) eV for conduction along c, the direction lying parallel to both the (${\mathrm{Cu}}_{2}$${\mathrm{O}}_{3}$) planes and the (${\mathrm{CuO}}_{2}$) chains. The magnetic susceptibility above 80 K follows a Curie-Weiss law with \ensuremath{\theta}=-95 K and ${p}_{\mathrm{eff}}$=0.65${\ensuremath{\mu}}_{B}$/Cu in the ac plane and \ensuremath{\theta}=-190 and ${p}_{\mathrm{eff}}$=0.94${\ensuremath{\mu}}_{B}$/Cu along b, the direction perpendicular to the (${\mathrm{Cu}}_{2}$${\mathrm{O}}_{3}$) planes and the (${\mathrm{CuO}}_{2}$) chains. There is an indication of antiferromagnetic order below ${T}_{N}$=60 K, and a Curie contribution at low temperature due to localized free spins [0.4(1) with S=(1/2 per formula]. The specific heat measured in the range 2--12 K is of the form ${\mathrm{AT}}^{\mathrm{\ensuremath{-}}2}$+\ensuremath{\gamma}T+\ensuremath{\beta}${T}^{3}$, where A=1080 mJ K/mole, \ensuremath{\gamma}=100 mJ/mole ${\mathrm{K}}^{2}$, and \ensuremath{\beta}=5.93 mJ/mole ${\mathrm{K}}^{3}$. A 5-T magnetic field greatly enhances the low-temperature specific heat, an effect which is attributed to the localized states with S=(1/2. The linear term is attributed to a localized density of states with no net spin, possibly associated with peroxide ions. The relevance of these results to the low-temperature specific heat of copper-oxide superconductors is discussed.