Metal–Organic Hybrid Interface States of A Ferromagnet/Organic Semiconductor Hybrid Junction as Basis For Engineering Spin Injection in Organic Spintronics

Abstract

Electrons in organic semiconductors (OSC) possess remarkably long spin relaxation times. Hybrid spintronic devices that combine OSC with ferromagnetic (FM) substrates are therefore expected to provide a route to devices with improved and new functionalities. A crucial role is played by the FM‐OSC interface which governs the spin injection into the OSC. Using spin‐resolved photoelectron spectroscopy and ab initio calculations we study here such possible injection channels in metal phthalocyanines (MPc). We report the first direct observation of the successful engineering of different spin‐selective hybrid interface states at the Fermi level of a FM‐OSC hybrid junction only by changing the central metal atom of a MPc. Our results demonstrate that tailoring the chemical interaction at the FM‐OSC interface is a promising way to modify the spin injection channels and thus the spin injection capability.

On the path toward organic spintronics

“…Shown are the magnetization densities computed with density functional theory for an iron-phthalocyanine molecule adsorbed on a cobalt surface. 3 The magnetization densities on the Fe and Co atoms couple ferromagnetically, as signifi ed by the orange isosurfaces, whereas the induced magnetization density on carbon atoms couples antiferromagnetically to the Co magnetization, as shown by the light-blue isosurface (image courtesy of Kartick Tarafder). An outline of the Fe-phthalocyanine molecule is shown in the inset (blue, gray, red, and white spheres depict nitrogen, carbon, iron, and hydrogen atoms, respectively).…”

“…The magnetization densities on the Fe and Co atoms couple ferromagnetically, as signifi ed by the orange magnetization density, but the magnetization density induced on carbon atoms couples antiferromagnetically to the Co magnetization (shown by the light-blue isosurfaces). 3 This exchange interaction arising between an organic molecule and a surface determines the electronic and magnetic structure of the entire system, and thus its understanding is crucial, complex, and limitless. The binding of the molecule to the surface through charge transfer between the molecule and surface (present in both physisorption and chemisorption processes) dictates their electronic and magnetic behavior, which in turn defi nes the functionality and stability of the system.…”

Recent progress in organic spintronics

“…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].…”

“…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.…”

Of interfaces and spin transport across nanoscale layers

“…In phenomenological models for the observed spin transport effects, the electronic structure, in particular the spin-polarization, of the MSC/FM interfaces plays a pivotal role in spin injection into the MSC [132]. This has prompted the suggestion that highly spin-polarized currents in spintronic devices may be obtained by exploiting such interface interactions, which has been dubbed "spinterface science" [137], and has motivated research into the role played by the interfaces [165,166,167,168,169,170,171].…”