Phase transitions in quasi-one-dimensional magnetic structures: Quantum effects

Semiclassical spin-wave theory leads to a low-temperature (kBTJ) static correlation function for a one-dimensional Heisenberg antiferromagnet having the approximate form 〈Sₓ(0)Sₓ(r)〉 r^-λe^-rξ, where ξ(T) is the classical correlation length and λ=2(πS)^-1 (S is the spin quantum number) is the quantum correction. This leads to a three-dimensional N\'eel temperature for exchange-coupled chains (with interchain exchange J_⊥), TN∝(J_⊥J)^1(2-λ). The magnetic field dependence of the quantum exponent λ is shown to lead to an important field dependence for TN.