Two dimensionality in quasi one-dimensional cobalt oxides

J. Sugiyama; H. Nozaki; J. H. Brewer; E. J. Ansaldo; T. Takami; H. Ikuta; U. Mizutani

doi:10.1103/PhysRevB.72.064418

paper

Two dimensionality in quasi one-dimensional cobalt oxides

arXiv:cond-mat/0501232 · doi:10.1103/PhysRevB.72.064418

Abstract

By means of muon spin rotation and relaxation ( $μ^{+}$ SR) techniques, we have investigated the magnetism of quasi one-dimensional (1D) cobalt oxides $A E_{n + 2}$ Co $_{n + 1}$ O $_{3 n + 3}$ ( $A E$ =Ca, Sr and Ba, $n$ =1, 2, 3, 5 and $\infty$ ), in which the 1D CoO $_{3}$ chain is surrounded by six equally spaced chains forming a triangular lattice in the $ab$ -plane, using polycrystalline samples, from room temperature down to 1.8 K. For the compounds with $n$ =1 - 5, transverse field $μ^{+}$ SR experiments showed the existence of a magnetic transition below $\sim$ 100 K. The onset temperature of the transition ( $T_{c}^{on}$ ) was found to decrease with $n$ ; from 100 K for $n$ =1 to 60 K for $n$ =5. A damped muon spin oscillation was observed only in the sample with $n$ =1 (Ca $_{3}$ Co $_{2}$ O $_{6}$ ), whereas only a fast relaxation obtained even at 1.8 K in the other three samples. In combination with the results of susceptibility measurements, this indicates that a two-dimensional short-range antiferromagnetic (AF) order appears below $T_{c}^{on}$ for all compounds with $n$ =1 - 5; but quasi-static long-range AF order formed only in Ca $_{3}$ Co $_{2}$ O $_{6}$ , below 25 K. For BaCoO $_{3}$ ( $n$ = $\infty$ ), as $T$ decreased from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF transition occurred at 15 K.

12 pages, 14 figures, and 2 tables