Spin Frustration, Magnetic Susceptibility and Excitations in Spatially Anisotropic Triangular-Lattice Antiferromagnets*

We calculate the temperature dependent magnetic susceptibility and excitation spectra for the spatially anisotropic triangular- lattice Heisenberg model. We show that suitably scaled plots of magnetic susceptibility provide a direct measure of frustration in the system and allow one to infer the exchange parameters from the susceptibility data. We find that the organic material $\kappa-(BEDT-TTF)_2Cu_2(CN)_3$ is very well described by the isotropic triangular lattice model. We also find that the excitation spectra of the model shows various anomalies in the Neel and Spiral phases.