The role of interfaces in organic spin valves revealed through spectroscopic and transport measurements

Abstract

Interfaces between dissimilar materials are critical to the performance of many electronic devices. In electrical devices where the active transport is through an organic semiconductor (OSC) layer there are metallic electrodes to supply and remove the charge carriers. At metal/molecule and molecule/metal interfaces the electrical contact is usually not Ohmic. As a result, in most metal-organic semiconductors-metal devices charge injection is mainly governed by tunneling across the barriers. When the metal electrodes are ferromagnetic the density of occupied and unoccupied electronic states is spindependent, which presents further subtleties to the electron transfer. In this article we summarize some of the important experimental results that have advanced our understanding of spin-polarized electron transfer across ferromagnetic metal (FM)/OSC interfaces. In particular, we highlight key spectroscopic studies that have revealed insights into the nature of the electronic structure between OSCs and FMs, in particular between Alq 3 and Co and Fe surfaces. We discuss the relationship between energy level diagrams for these systems and transport measurements made on spin-valve devices.

Organic Spin Valves: A Review

“…Transport of SP carriers from the first FM electrode to the second depends upon the coupling between the FM and OSC at the interface (that affects spinterface) and the spacer properties such as spin scattering sources including HFI and SOC and carrier mobility which is affected by disorder, impurities, temperature etc . of the materials . In general, the spin polarization of the transport electrons in the OSCs is attenuated exponentially as e –d/λ S when electrons diffuse across the organic spacer with the thickness, d .…”

“…In addition to spin valve effect, a different type of MR effect in OLEDs, the so‐called organic magnetoresistance (OMAR) has also been observed in a range of OSCs . Excellent reviews on different aspects of the organic spintronic devices can be found in the literature …”

Sign Control of Magnetoresistance Through Chemically Engineered Interfaces

“…These samples have allowed us to study the inorganic materials excluding possible contributions arising from the molecular layer, such as changes of the vacuum level of the OS. [ 6,14 ] Two different structures, related to those with BPhen studied above, were produced. Sample (C) is composed of Co (8) (10), with the LiF layer above the ferromagnetic electrode.…”

Spin-polarization reversal at the interface between benzene and Fe(100)

“…The complex nature of organic/inorganic ferromagnetic interfaces has been emphasized in recent publications. 4,5,[9][10][11] In particular, the specific chemical bonding between the adsorbed organic molecule and the ferromagnetic surface is expected to dramatically influence the polarization of the injected electrons. For instance, the spin polarization at the Co=Alq 3 and ðLa; SrÞMnO 3 =Alq 3 interfaces has been found positive in Ref.…”