Thermodynamics of a one-dimensional frustrated spin-1/2 Heisenberg ferromagnet

We calculate the thermodynamic quantities (correlation functions (S0Sn), correlation length, spin susceptibility X, and specific heat CV) of the frustrated one-dimensional spin-half J(1)-J(2) Heisenberg ferromagnet, i.e., for J(2) < 0.25 vertical bar J(1)vertical bar, using a rotation-invariant Green's-function formalism and full diagonalization of finite lattices. We find that the critical indices are not changed by J(2), i.e., chi = y(0)T(-2) and epsilon = y(0)T(-1) at T -> 0. However, the coefficients y(0) and x(0) linearly decrease with increasing J(2) according to the relations y(0) = (1-4J(2)/vertical bar J(1)vertical bar)/24 and x(0) =(1-4J(2)/vertical bar J(1)vertical bar))/4, i.e., both coefficients vanish at J(2) = 0.25 vertical bar J(1)vertical bar indicating the zero-temperature phase transition that is accompanied by a change in the low-temperature behavior of chi (xi) from chi proportional to T-2 (xi proportional to T-1) at J(2) <0.25 vertical bar J(1)vertical bar to chi proportional to T-3/2 (xi proportional to T-1/2) at J(2) = 0.25 vertical bar J(1)vertical bar. In addition, we detect the existence of an additional low-temperature maximum in the specific heat when approaching the critical point at J(2) = 0.25 vertical bar J(1)vertical bar.