Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

Abstract

Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al2O3 or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al2O3/Alq3/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer.

Probing electron-phonon excitations in molecular junctions by quantum interference

“…Inelastic signals at these energies are also clearly seen in the DFT calculated IETS (see Supplementary Information ). Vibration excitation spectra in the same energy range has been recently reported also for Alq 3 based molecular junctions with a similar cross-bar geometry 31 .…”

A multifunctional molecular spintronic platform with magnetoresistive and memristive responses via a self-assembled monolayer

“…[4][5][6][7] However, the creation of such hetero-junctions with well-defined organic/FM interfaces, which are sensitively impacted by the growth condition and the materials' compatibility, is a great challenge. [8][9][10][11] Upon the contact of organic and FM materials, issues like the molecular ordering and the interlayer diffusion and interaction not only affect the transport properties of the junction but also entangle with one another, complicating the investigation. 9,12,13 Recently, the techniques of the Langmuir-Blodgett (LB) film and the selfassembled monolayer (SAM) with a large-area junction have been proposed for solving the complicated active-layer problem and have been adopted in several nano-scale devices.…”

Magnetic-State Controlled Molecular Vibrational Dynamics at Buried Molecular–Metal Interfaces

“…For the organic magnetic tunnel junctions, the conductance signals are averaged over a large number of molecules forming either barrier or contacting extended ferromagnetic electrodes. To our best knowledge, the only study of the IETS in molecular spintronics just aimed to obtain structural information on the integrity of the Alq 3 barrier by localizing junctions with pin-holes where no signatures of molecular vibrational modes were present 12 . As we shall see below, for the high quality buried molecular-metal interfaces with only small percentage on the molecules weakly contacting the electrode, the detailed investigation of the buried molecule-metal interfaces could be carried out by analyzing vibrational heating of the molecules in locally distributed hot spots.…”