Direct observation of a highly spin-polarized organic spinterface at room temperature

Abstract

Organic semiconductors constitute promising candidates toward large-scale electronic circuits that are entirely spintronics-driven. Toward this goal, tunneling magnetoresistance values above 300% at low temperature suggested the presence of highly spin-polarized device interfaces. However, such spinterfaces have not been observed directly, let alone at room temperature. Thanks to experiments and theory on the model spinterface between phthalocyanine molecules and a Co single crystal surface, we clearly evidence a highly efficient spinterface. Spin-polarised direct and inverse photoemission experiments reveal a high degree of spin polarisation at room temperature at this interface. We measured a magnetic moment on the molecule's nitrogen π orbitals, which substantiates an ab-initio theoretical description of highly spin-polarised charge conduction across the interface due to differing spinterface formation mechanisms in each spin channel. We propose, through this example, a recipe to engineer simple organic-inorganic interfaces with remarkable spintronic properties that can endure well above room temperature.

Recent progress in organic spintronics

“…with a flat ring structure) π-conjugated molecules have been studied. In particular, metal-phthalocyanines (Pc's) and porphyrins have received a considerable amount of attention [89,93,96,97,99,[103][104][105]107]. The metal ions in these metallo-organic molecules typically have unpaired spins, which are found to couple to the ferromagnetic substrate via the exchange interaction.…”

“…This has been studied in some detail for various π-conjugated molecules adsorbed on ferromagnetic surfaces. The most common experimental techniques to probe the interface electronic and magnetic structure are x-ray magnetic circular dichroism (XMCD) [93][94][95], spin-polarized scanning tunneling microscopy (SP-STM) [90,[96][97][98], spin-polarized metastable de-excitation spectroscopy(SP-MDS) [99][100][101], spin-polarized ultraviolet photoelectron spectroscopy (SP_UPS) [102][103][104], and spin-resolved two-photon photoemission (SR-2PPE) [77]. Modeling is typically done with density functional theory (DFT) [89,95,97,98,[104][105][106][107][108][109].…”

Of interfaces and spin transport across nanoscale layers

“…Photoemission spectroscopy or scanning tunneling microscopy, combined with first-principles calculations, enable a detailed analysis of the spin-dependent electronic properties of metal-organic interfaces. Bonding between a molecule and a ferromagnetic metal leads to spin-split (anti)bonding states and induces a spin polarization that extends onto the molecule [138,139,140,141,157,175,14,142]. For instance, calculations on C 60 |Fe(001) interfaces yield a magnetic moment of 0.2 µ B induced on the C 60 molecules [14].…”

“…It has been suggested that highly spin-polarized currents in spintronic devices may be obtained by exploiting the spin-dependent interaction between molecular materials and ferromagnetic electrodes, which has been coined "spinterface science" [137]. The spin-dependent electronic structure of metal-organic interfaces is accessible through photoemission spectroscopy, scanning tunneling microscopy (STM), and first-principles calculations [138,139,140,141,14,142].…”

Spintronic effects at nickel-graphene interfaces

“…At the interface between the materials phenomena like orbital hybridisation and charge transfer can greatly influence the transport of spins across the interface. Spin polarised microscopy and spectroscopy techniques have shown these effects to be typically spin dependent, resulting in a hybrid interface with magnetic properties that are quite different from those of the bulk ferromagnet (Djeghloul et al, 2013;Lach et al, 2012;Rizzini et al, 2014;Sun et al, 2014;Suzuki et al, 2002Suzuki et al, , 2004Tran et al, 2013). It is a topic of active study how this effects the spin transport across the interface Kawahara et al, 2012;Raman et al, 2013;Schmaus et al, 2011;Steil et al, 2013).…”