Giant magnetoresistance due to orbital-symmetry mismatch in transition metal benzene sandwich molecules

Abstract

Achieving large magnetoresistance (MR) effects in atomic-scale junctions is of great importance in the field of molecular spintronics. In this work, using ab initio quantum transport calculations, we report on the spin transport properties of molecular junctions made of single transition metal benzene sandwich molecules $(\mathrm{TM}{\mathrm{Bz}}_{2})$ bridged by ferromagnetic electrodes. We find that relative magnetic orientations of two electrodes and the molecule can dramatically affect low-bias transport properties of the junction. While the $\mathrm{TM}{\mathrm{Bz}}_{2}$ are insulating in the gas phase, their corresponding molecular junctions bridged between the two electrodes are half-metallic minority-spin conductors (i.e., almost 100% spin polarization) and display very large MR. More interestingly, even larger molecular MR, corresponding to a reversal of molecular spin moment, are found due to the spin-valve behavior of the molecule controlled by the magnetic impurity. Such a particular performance is attributed to strong spin-selective hybridization of electronic states at the molecule/metal interface due to orbital-symmetry mismatch between the electrode's and molecular states. We also discuss the importance of the shape of electrodes on spin transport efficiency.