Doping evolution of itinerant magnetic fluctuations in Fe-based pnictides

¹  Max-Planck-Institut für Physik Komplexer Systeme - 01187 Dresden, Germany, EU
²  L.V. Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences - 660036 Krasnoyarsk, Russia
³  Institute für Mathematische und Theoretische Physik, TU-Braunschweig - 38106 Braunschweig, Germany, EU

Corresponding authors: maxim@pks.mpg.de ieremin@pks.mpg.de

Received: 20 May 2008
Accepted: 24 July 2008

Abstract

Employing the four-band tight-binding model, we study theoretically the doping dependence of the spin response in the normal state of novel Fe-based pnictide superconductors. We show that the commensurate spin density wave (SDW) transition that arises due to interband scattering between the hole α-pockets and the electron -pockets disappears already at the doping concentration x ≈ 0.04 reflecting the evolution of the Fermi surfaces. Correspondingly, with further increase of the doping the antiferromagnetic fluctuations are suppressed for and the imaginary part of the spin susceptibility at antiferromagnetic wave vector becomes nearly temperature independent. At the same time, we observe that the uniform susceptibility deviates from the Pauli-like behavior and is increasing with increasing temperature reflecting the activation processes for the α-Fermi surfaces up to temperatures of about T = 800 K. With increase of the doping the absolute value of the uniform susceptibility lowers and its temperature dependence changes. In particular, it is a constant at low temperatures and then decreases with increasing temperature. We discuss our results in a context of recent experimental data.