Suppression of Magnetic Frustration by Doping in a nearest-neighbour   anti-ferromagnetic triangular lattice
  Based on experimental observations in A{x}MO{2} (A = Na, Li; M = Co, Ni), a model for suppression of magnetic frustration by electron doping in a nearest-neighbour antiferromagnetic triangular lattice is presented. It is found that frustration can be quantified, as determined by geometry and bond-counting, and its magnitude is a non-monotonic function of $x$. A mean-field calculation provides temperature-dependent magnetization, spin-entropy and heat capacity. Low-doping (x = 0.25, 0.33) results in a highly frustrated regime. A{0.5}MO{2} has strongest order and no frustration, while high doping (x = 0.67, 0.75) leads to low frustration and higher spin-entropy. The results agree with experiments including neutron scattering, spin entropy-driven thermoelectricity and ion ordering. 
K. Sheshadri and A. Chainani