Proton NMR in a Random Mixture with Competing Anisotropies: CsMn_1−xCo_xCl₃·2H₂O

Abstract

Proton NMR measurements were carried out to clarify the spin structure in the intermediate phase of CsMn_1−xCo_xCl₃·2H₂O. Hyperfine fields at proton sites are compared with the calculated values of dipole fields. In Mn-rich antiferromagnetic phase, the moments including Co impurities point to the b-axis, while in Co-“rich” antiferromagnetic phase, most of the moments point to the c-axis. In the intermediate phase, three kinds of NMR lines were observed which are due to the moments parallel to the b-axis, c-axis and distributed in the bc-plane. The fraction of the moments parallel to the c-axis increases with increasing Co concentration. It is shown that in the intermediate phase the b- and c-axis domains coexist, and at the boundary of both domains the moments tilt continuously from the b- to c-axis. The tilting of the averaged moment is achieved by the change in the fraction of each domain. This model is supported by the fact that the relative intensities of the peaks change with an external field.