Electron Spin Resonance in Second-Stage NiCl₂-Graphite Intercalation Compound

Abstract

ESR measurements have been made at 9 GHz in the temperature range 4.2 K≤T≤300 K, on the second-stage NiCl₂-graphite intercalation compound based on a single crystal of Kish graphite, which approximates to an ideal two-dimensional ferromagnet in the presence of an external magnetic field. The angular and temperature dependences of the ESR resonance field and line-width show that the spin symmetry of this system changes from XY-like to Heisenberg-like at ∼T_g (≅30 K) as the temperature increases. The experimental results on ESR at sufficiently high temperatures above T_g are qualitatively explained in terms of the magnetic behaviour of the two-dimensional Heisenberg-like ferromagnet.