Spin-polarized electrical transport in transition metal encapsulated C20 fullerenes: A theoretical account

Abstract

This work delves into the conductance property of transition metal (Ti, V, Cr, Mn, Fe, Co, Ni) encapsulated C20 endohedral metallofullerenes (EMFs), sandwiched between non-magnetic gold electrodes. DFT optimization of the designed systems casts the encapsulated metal at the center of the C20 cage irrespective of the system and spin states. Application of density functional theory coupled with non-equilibrium green function techniques on these EMFs results variant transport characteristics for different metal encapsulation, represented through transmission spectra at zero bias and current vs. voltage (I-V) plots. Spin-polarized electrical transport has been observed for the Mn, Fe, Co and Ni encapsulated C20, while no such spin polarization could be traced for Ti, V and Cr both in absence and presence of applied bias. The EMFs with Mn, Fe, Co and Ni display half-metallic behavior and significant spin-filtering efficiency, which reaches maximum value for the Fe encapsulated C20. Spin-resolved electrical conductance in the Mn/Fe/Co/Ni-EMFs are explained by density of states, projected density of states at zero bias and molecular orbital analyses, which reveal the contribution of C20 electrons towards the down-spin-polarized transmission for Fe/Co/Ni-EMFs, while for the Mn-EMF, the metal d-electrons mostly participate in the up-spin-polarized transmission. Taken these observations together, the present computational study showcases the importance of encapsulating transition metal inside carbon cages in inducing spin polarization and thus provides an aid to tailor suitable molecules for spintronic applications.