ESR Study of the Triangular Lattice Heisenberg Antiferromagnets VX₂ (X=Cl, Br and I)

Abstract

ESR signals from the 2D triangular lattice antiferromagnet VX₂ have been studied in detail in paramagnetic and ordered phases. At high T, the shift and the width are nearly isotropic and an intense exchange narrowed Lorentzian peak is observed. When T is lowered toward the transition point T_s, rapid increase in width and down shift of the resonance field as seen in the spin-glass occur. For T<T_s, however, an extremely strong absorption line reappears when the field is applied normal to the c-axis. This signal becomes sharp and shifts rapidly toward the lower field with T→0 K. Many unusual behaviors which can not be observed in the non-frustrated systems are observable though we can not yet interpret them successfully.