Eur. Phys. J. B (2014) 87: 112
https://doi.org/10.1140/epjb/e2014-50152-y

Regular Article

Magnetic susceptibility and short-range order in iron pnictides: Anisotropic J₁-J₂ Heisenberg model

¹ Joint Institute for Nuclear Research, 141980 Dubna, Russia
² Institut für Theoretische Physik, Universität Leipzig, 04109 Leipzig, Germany

^a e-mail: plakida@theor.jinr.ru

Received: 7 March 2014
Published online: 15 May 2014

Abstract

A spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the anisotropic non-frustrated J₁-J₂ model for the iron pnictides AFe₂As₂ (A = Ca, Sr, Ba) is presented. The two-spin correlation functions, the spin-excitation spectrum, and the staggered magnetization are calculated self-consistently as functions of temperature and spin. The temperature dependence of the magnetic (uniform static) susceptibility, in particular the linear increase with T in a wide temperature region that is in good quantitative agreement with experiments, is ascribed to a strong in-plane antiferromagnetic short-range order. The values of the Néel temperature resulting from the localized spin model with realistic out-of-plane couplings are found to be much higher than the measured values. From this an extension of the model by including itinerant degrees of freedom is suggested.