d-electron mediated 4f(7)-4f(7) exchange in Gd-rich compounds; spin density functional study of Gd2Cl3

摘要

Spin-density functional theory (SDFT) calculations of the d-f exchange coupling for the pseudo-one-dimensional (pseudo-1-D) chain compound Gd2Cl3 has been carried out using the 1-D model, Gd8Cl12(OPH3)(4), by considering seven variations in the ordering of the 4f(7) moments. The calculations indicate that this semiconducting system should exhibit antiferromagnetic ordering of the 4f(7) moments in a pattern consistent with published neutron diffraction data. An attempt to account for the calculated magnetic energies of spin patterns using an Ising model was unsuccessful, indicating that the latter model is inappropriate. The qualitative features can be interpreted using a perturbative molecular orbital model that focuses on the influence of the 4f(7)-d exchange interaction on the d-based molecular orbitals. Fundamental to the d-electron-mediated exchange mechanism is the intra-atomic 4f(7)-d exchange interaction. The essence of this interaction is present in the Gd atom [4f(7)5d(1)6s(2)], which is computationally investigated within SDFT. In Gd2Cl3, the d-electron-mediated f-f exchange interaction was interpreted using basic perturbation theory. Computed density of states and spin polarization information was used to support the perturbation-theoretic analysis. (C) 2003 Elsevier Inc. All rights reserved. [References: 52]