Thermodynamics of the frustrated J(1)-J(2) Heisenberg ferromagnet on the body-centered cubic lattice with arbitrary spin

摘要

We use the spin-rotation-invariant Green's function method as well as the high-temperature expansion to discuss the thermodynamic properties of the frustrated spin-S J(1)-J(2) Heisenberg magnet on the body-centered cubic lattice. We consider ferromagnetic nearest-neighbor bonds J(1) < 0 and antiferromagnetic next-nearest-neighbor bonds J2 >= 0 and arbitrary spin S. We find that the transition point J(2)(c) between the ferromagnetic ground state and the antiferromagnetic one is nearly independent of the spin S, i.e., it is very close to the classical transition point J(2)(c,clas) = 2/3 vertical bar J(1)vertical bar. At finite temperatures we focus on the parameter regime J(2) < J(2)(c) with a ferromagnetic ground-state. We calculate the Curie temperature T-C(S, J(2)) and derive an empirical formula describing the influence of the frustration parameter J(2) and spin S on T-C. We find that the Curie temperature monotonically decreases with increasing frustration J(2), where very close to J(2)(c,clas) the T-C(J(2))-curve exhibits a fast decay which is well described by a logarithmic term 1/log(2/3 vertical bar J(1)vertical bar - J(2)). To characterize the magnetic ordering below and above TC, we calculate the spin-spin correlation functions < S0SR >, the spontaneous magnetization, the uniform static susceptibility chi(0) as well as the correlation length xi. Moreover, we discuss the specific heat C-V and the temperature dependence of the excitation spectrum. As approaching the transition point J(2)(c) some unusual features were found, such as negative spin-spin correlations at temperatures above T-C even though the ground state is ferromagnetic or an increase of the spin stiffness with growing temperature.