Low-dimensional magnetism in the mixed Cr valence spin-chain compound Sr_4Cr_3O_9

Abstract

Sr4Cr3O9 is the n = 2 member of a family of quasi-one-dimensional compounds An+2Tn+1O3n+3 (A = Ca, Sr, or Ba, T = transition metal, and n = 1 − ∞) having a crystal structure which consists of chains of nT O6 octahedra alternated by one T O6 trigonal prism running along the caxis. The chains are arranged on a triangular lattice in the ab-plane. We report the synthesis, structure, magnetization M versus magnetic field H, magnetic susceptibility χ versus temperature T and specific heat C versus T measurements on sintered and arc-melted polycrystalline samples of Sr4Cr3O9. The χ data have a T depdendence which is typical of low-dimensional magnetic systems with dominant antiferromagnetic (AF) exchange interactions. Specifically, χ(T ) shows a broad maximum at Tmax ≈ 200 K for the sintered pellet and Tmax ≈ 265 K for the arc-melted sample, indicating the onset of short-range magnetic order. Below T = 15 K we observe 2 anomalies in the χ(T ) data for both samples suggesting the onset of long-range magnetic ordering. The corresponding anomalies in the C(T ) data however are weak indicating that only a small amount of the expected magnetic entropy is recovered at the magnetic transitions and that strong short-range AF order exists above these temperatures.