A tight-binding method for predicting magnetic ordering in Gd-containing solids: Application to GdB2C2

Herein we present a method to compute d-f mediated exchange coupling in Gd-containing systems with a spin-dependent extended Hückel-tight binding (EHTB) method. EHTB parameters were chosen to exactly reproduce the spin density functional calculation (SDFT) energy gap of the S = 45/2 and 39/2 spin patterns for a model compound, Gd6CoI12(OPH3)6. Comparison between SDFT and EHTB results shows a good match between the spin-pattern energy distribution for the two methods. We applied our EHTB method to the solid-state compound GdB2C2 by considering 6 different variations in the ordering of the 4f7 moments. Calculations indicate that this metallic system should exhibit antiferromagnetic ordering of the 4f7 moments with a magnetic structure consistent with published neutron diffraction results.