Far-Infrared Absorption in CoCl2·2H2O

Abstract

Measurements of the magnetic resonance absorption in ${\mathrm{CoCl}}_2\text{·2}{\mathrm{H}}_2\mathrm{O}$ over the frequency range from 18 to 50 cm⁻¹ are briefly reported. Resonance lines are observed in fields up to 55 kOe, covering all three of its magnetic phases. The rather complex spectrum suggests that we observe not only simple, single excitations but also clustered, multiple ones, in which $\text{m\hspace{0.17em}>\hspace{0.17em}1}$ spins are flipped. The energy required to create such an $\mathrm{m‐}\mathrm{fold}$ excitation is much less than $m$ times the energy to create a single excitation. This and other major features of the experimental data are accounted for by application of the cluster model of Date and Motokawa, which describes spin clusters in the ferromagnetic chains of ${\mathrm{CoCl}}_2\text{·2}{\mathrm{H}}_2\mathrm{O}$ .