Effect of the Two Dimensional Property in NiCl2 on the Temperature Dependence of the Antiferromagnetic Resonance Point

Electron spin resonances in the hexagonal layer type compound NiCl 2 in the ordered state have been studied in detail by using microwaves of 10∼70 GHz regions. Considering the resonance data together with other facts, a possible model for the spin arrangement in NiCl 2 in which spins lie in the c -planes by making adjacent ferromagnetic layers which alternate in direction along the c -axis is obtained. The temperature dependence of the resonance point ( H 0 // c -axis) can not be explained by the molecular field theory. A spin-wave calculation which takes into account a two-dimensional property in this salt gives the following temperature dependence of the resonance frequency, \(hν{=}√{(g//μBH)²+|J'|z'SD(S-1/2)}-AT∑_{n{=}1}∞(1/n)exp(-√8|J'|z'SD(S-1/2){·}n/kBT)+BT²∑_{n{=}1}∞(1/n²)exp(-√8|J'|z'SD(S-1/2){·}n/KBT)\). A quantitative agreement between the theory and the experiment is attained.