Magnetic Studies of the Canted Ising Linear Chain CsCoCl3·2H2O

Abstract

Specific-heat, nuclear-magnetic-resonance, magnetic-susceptibility, magnetization, and antiferromagnetic-resonance measurements on the orthorhombic crystal CsCo${\mathrm{Cl}}_3$·2${\mathrm{H}}_2$O have led to the following model of the magnetic structure and the exchange interactions: The interaction is Ising-like with very strong exchange along the $\overrightarrow{\mathrm{a}}$ axis resulting in canted-antiferromagnetic chains lying in the $\mathrm{ac}$ plane with their moments 10° from the $\overrightarrow{\mathrm{c}}$ axis and a net moment in the $\overrightarrow{\mathrm{a}}$ direction. At $T_N=3.38\mathrm{}$ K the chains in each $\mathrm{ac}$ plane couple ferromagnetically so that their net moments are all in the same sense, but with the net moments in alternate planes antiparallel. At a critical field of 2.9 kOe at 1.1 K ($\overrightarrow{\mathrm{H}}$ applied along the $\overrightarrow{\mathrm{a}}$ axis) the moments in half of the planes reverse giving rise to an induced ferromagnetic moment parallel to the $\overrightarrow{\mathrm{a}}$ axis. At temperatures well above $T_N$ the strong Ising interaction produces correlations which manifest themselves as a large induced moment at relatively modest fields. The general features of these experimental results have been reproduced using a Hamiltonian which includes Ising and Dzyaloshinsky-Moriya terms for the interaction along the $\overrightarrow{\mathrm{a}}$ axis and isotropic terms for the interactions along $\overrightarrow{\mathrm{b}}$ and $\overrightarrow{\mathrm{c}}$. Applying this Hamiltonian to the critical-field and antiferromagnetic-resonance data, we obtain the following values: $J^a=-13\mathrm{}$ K, $J^b=-0.2\mathrm{}$ K, $J^c=+4.5\mathrm{}$ K, and $D=+3.6\mathrm{}$ K. These numerical values are the result of applying a very simplified model to a very complex system and thus must be considered as qualitative rather than quantitative.