Design of the Local Spin Polarization at the Organic-Ferromagnetic Interface

Abstract

By means of ab initio calculations and spin-polarized scanning tunneling microscopy experiments we show how to manipulate the local spin-polarization of a ferromagnetic surface by creating a complex energy dependent magnetic structure. We demonstrate this novel effect by adsorbing organic molecules containing π(pz)-electrons onto a ferromagnetic surface, in which the hybridization of the out-of-plane pz atomic type orbitals with the d-states of the metal leads to the inversion of the spin-polarization at the organic site due to a pz − d Zener exchange type mechanism. As a key result, we demonstrate that it is possible to selectively inject spin-up and spin-down electrons from the same ferromagnetic surface, an effect which can be exploited in future spintronic devices.PACS numbers: 68.43.Bc,71.15.Mb Combining molecular electronics with spintronics represents one of the most exciting avenues in building future nanoelectronic devices [1][2][3]. For example, widely used in spintronic applications, the spin valve [4] is a layered structure of two ferromagnetic electrodes separated by a nonmagnetic spacer to decouple the two electrodes and allows spin-polarized electrons to travel through it. The efficiency of a spin valve depends crucially on the spin injection into and spin transport throughout the nonmagnetic spacer. On one side, since organic molecules are made of light elements with weak spin-orbit coupling as C and H, their use as spacer materials is very promising for transport properties since the spin coherence over time and distance is much larger than in the conventional semiconductors present in today's devices [5][6][7]. On the other side, the spin injection is mostly controlled by the ferromagnetic-organic layer interface [8,9] which is responsible for the significant spin loss in devices [10]. Therefore, a large effort is made to control the electronic properties at the organic-magnetic interfaces and, in this context, the theoretical first-principles calculations represent an indispensable tool to understand and guide experiments toward more efficient devices.In this Letter we propose a simple way to manipulate the local spin-polarization of a ferromagnetic surface by flat adsorbing organic molecules containing π(p z )-electrons onto it. As a consequence, around the Fermi level an inversion of the local spin-polarization at the organic site occurs with respect to the ferromagnetic surface due to a complex energy-and spin-dependent electronic structure of the organic-metal interface. The interaction between the molecule and the ferromagnetic surface reveals a mechanism similar to the p z − d Zener exchange [11] and enables a selective control of electron injection with different spins [i.e. up(↑) or down(↓)] from the same ferromagnetic surface within a specific energy The pz atomic orbitals in the spin-up channel hybridize with the majority (spin-up) states of the Fe atoms forming bonding (at lower energies) and antibonding (at higher energies) states some of them being pushed above the Fermi level...

Interface-engineered templates for molecular spin memory devices

“…The Co electrode with spin polarized s-p electrons serves as the spin-polarizer, and the interface magnetic layer with spin-dependent interface resistance serves as the spin analyser, giving rise to IMR. Chemical modification of the ferromagnet/ZMP molecule interface arises owing to charge transfer and hybridization of the molecular orbitals with the d-orbitals of the ferromagnet, creating new hybrid metal-organic interface states that directly affect the electronic and magnetic properties of the adsorbed molecule 24 . These interactions strongly depend on the specific molecular structure and morphology 25,26 , influencing the efficiency of spin Karthik …”

Adsorption of tris(8-hydroxyquinoline)aluminum molecules on cobalt surfaces

“…The electronic structure at interfaces between organic molecules and metallic electrodes, especially the alignment of energy levels of molecules and the Fermi level of metal electrodes, is critical for charge and spin injection 17 . Metals with low work functions have been widely used as negative electrodes in electroluminescence devices 18 to decrease hole injection energy barrier.…”

“…In organic spin valves, the interfacial orbital hybridizations between the first layer of organic molecules and magnetic electrodes plays a key role in spin injection 5 . Strong hybridization may change the sign of the spin-polarization of magnetic surfaces 17 . Barraud et al (ref.…”

Electronic and magnetic properties of Fe clusters inside finite zigzag single-wall carbon nanotubes

“…This induced magnetization is similar to that recently obtained, both experimentally and by DFT calculations, in the interaction of aromatic molecules with a ferromagnetic substrate. 19 …”

“…18 Furthermore, as far as finite ZNTs can be considered as organic molecules containing π electrons, our results can be useful in the interpretation of the local spin polarization at the organicferromagnetic interface, which has been recently described both theoretically and experimentally. 19 Previous calculations of the electronic structure of 3d transition-metal atoms and clusters bonded to carbon nanostructures have considered infinitely long carbon nanotubes, [20][21][22][23][24][25][26][27][28] an infinite graphene sheet, 26,29,30 capped finite ZNTs, 31,32 or finite nanotubes with unsaturated open ends. 33 The effects due to the edge states have not been analyzed in those works.…”