paper

Thermodynamics of the frustrated - Heisenberg ferromagnet on the body-centered cubic lattice with arbitrary spin

arXiv:1505.07219 · doi:10.1140/epjb/e2015-60113-7

Abstract

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- - Heisenberg magnet on the body-centered cubic lattice. We consider ferromagnetic nearest-neighbor bonds and antiferromagnetic next-nearest-neighbor bonds and arbitrary spin . We find that the transition point between the ferromagnetic ground state and the antiferromagnetic one is nearly independent of the spin , i.e., it is very close to the classical transition point . At finite temperatures we focus on the parameter regime with a ferromagnetic ground-state. We calculate the Curie temperature and derive an empirical formula describing the influence of the frustration parameter and spin on . We find that the Curie temperature monotonically decreases with increasing frustration , where very close to the -curve exhibits a fast decay which is well described by a logarithmic term . To characterize the magnetic ordering below and above , we calculate the spin-spin correlation functions , the spontaneous magnetization, the uniform static susceptibility as well as the correlation length . Moreover, we discuss the specific heat and the temperature dependence of the excitation spectrum. As approaching the transition point some unusual features were found, such as negative spin-spin correlations at temperatures above even though the ground state is ferromagnetic or an increase of the spin stiffness with growing temperature.

19 pages, 10 figures, version as in EPJB

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