Metamagnetism of Co${\mathrm{Cl}}_3$ [(C${\mathrm{H}}_3$${)}_3$NH] · 2${\mathrm{H}}_2$O

If a field $H>\mathrm{}64\mathrm{}$ Oe is applied along the $c$ axis of Co${\mathrm{Cl}}_3$[(C${\mathrm{H}}_3$ ${)}_3$NH] · 2${\mathrm{H}}_2$O, the proton and chlorine NMR frequencies exhibit anomalous behavior which may be explained by a metamagnetic model in which all spins in certain $bc$ planes reverse their directions. By minimizing the expressions for the energy of such a system, we derive the internal fields that arise from such a metamagnetic transition. It is shown that such internal fields yield the observed form of the field and angle dependence of the NMR frequencies. The observed angle dependence of the magnetization is also obtained from this model.