Magnetic properties of novel FeSe(Te) superconductors

Magnetization studies were carried out for the novel FeSe1-xTex superconductors (0 <= x <= 1) to investigate a behavior of the intrinsic magnetic susceptibility chi in the normal state. The magnetic susceptibility was found to increase gradually with Te content. The temperature dependencies of the magnetic susceptibility chi and its anisotropy Delta chi = chi(parallel to)-chi(perpendicular to) were measured for FeSe in the temperature range 4.2-300 K, and a growth of susceptibility with temperature was revealed. For FeTe a substantial increase of chi under pressure was found. Ab initio calculations of the band structure and magnetic susceptibility have shown, that FeSe1-xTex systems are close to magnetic instability with dominating enhanced spin paramagnetism. The calculated paramagnetic susceptibility exhibits a strong dependence on the unit cell volume V and especially the height of chalcogen species from the Fe plane. With appropriate values of these parameters the calculations have reproduced the experimental data on chi(T) and chi(P) for FeSe and FeTe, respectively. (C) 2012 Elsevier B.V. All rights reserved.