Electronic structure and magnetic properties of metallocene multiple-decker sandwich nanowires

Abstract

We present a study of the electronic and magnetic properties of the multiple-decker sandwich nanowires ($CP$-M) composed of cyclopentadienyl ($\mathit{CP}$) rings and $3d$ transition-metal atoms (M = Ti to Ni) using first-principles techniques. We demonstrate using density functional theory that structural relaxation plays an important role in determining the magnetic ground state of the system. Notably, the computed magnetic moment is zero in $CP$-Mn, while in $CP$-V a significant turn-up in magnetic moment is evidenced. Two compounds show a half-metallic ferromagnetic ground state $CP$-Fe/Cr with a gap within the minority/majority spin channel. In order to study the effect of electronic correlations upon the half-metallic ground states in $CP$-Cr, we introduce a simplified three-band Hubbard model which is solved within the variational cluster approach. We discuss the results as a function of size of the reference cluster and the strength of average Coulomb $U$ and exchange $J$ parameters. Our results demonstrate that for the range of studied parameters $U=2$--4 eV and $J=0.6$--1.2 eV the half-metallic character is not maintained in the presence of local Coulomb interactions.