Magnetic behavior of Co ions in the exotic spin-chain compound,Ca3Co2O6, from 59Co NMR studies

TL;DR

This study uses 59Co NMR to investigate the magnetic properties of Ca3Co2O6, revealing the presence of non-magnetic Co ions and providing microscopic evidence for a magnetic transition at 12 K.

Contribution

First NMR investigation of Ca3Co2O6, identifying non-magnetic Co ions and elucidating the 12 K magnetic transition at a microscopic level.

Findings

Detection of non-magnetic Co ions around 10 K

Dramatic increase in relaxation times below 12 K

Confirmation of a magnetic transition at 12 K

Abstract

We have performed field-swept 59Co NMR measurements on the 'exotic' spin-chain material, Ca3Co2O6, crystallizing in K4CdCl6-type rhombohedral structure, believed to exhibit two magnetic transition temperatures (around 24 and 12 K). This is the first NMR investigation of this family of compounds. We are able to detect the NMR signal below about 15 K, which is a conclusive proof for the existence of non-magnetic Co ions (Co3+ - low-spin 3d6, in addition to magnetic Co ions) at least in a narrow temperature range around 10 K, thereby resolving a controversy on this issue in the literature. In addition, we find that the spin-lattice and spin-spin relaxation times undergo a dramatic increase below about 12 K, with a profound influence on the intensity of the NMR signal as a function of temperature, providing a microscopic evidence for the existence of 12K-transition. The spectral features present quite an interesting situation.