Unidirectional Spin-Dependent Molecule-Ferromagnet Hybridized States Anisotropy in Cobalt Phthalocyanine Based Magnetic Tunnel Junctions

Abstract

Organic or molecular spintronics is a rising field of research at the frontier between condensed matter physics and chemistry. It aims to mix spin physics and the richness of chemistry towards designing new properties for spin electronics devices through engineering at the molecular scale. Beyond the expectation of a long spin lifetime, molecules can be also used to tailor the spin polarization of the injected current through the spin-dependent hybridization between molecules and ferromagnetic electrodes. In this Letter, we provide direct evidence of a hybrid interface spin polarization reversal due to the differing hybridization between phthalocyanine molecules and each cobalt electrode in Co/CoPc/Co magnetic tunnel junctions. Tunnel magnetoresistance and anisotropic tunnel magnetoresistance experiments show that interfacial hybridized electronic states have a unidirectional anisotropy that can be controlled by an electric field and that spin hybridization at the bottom and top interfaces differ, leading to an inverse tunnel magnetoresistance.

Anisotropy and Damping of Molecules/Cobalt Hybrid Thin Films

“…Using the above mentioned bulk parameters, from the measured frequency variation δF ≈ 0.5 GHz, we obtain a variation of the anisotropy field δH K ≈ 0.048 T corresponding to a variation of the anisotropy constant δK ≈ 51 kJ/m 3 . Our results are consistent with the studies reporting that organic molecules affect the surface magnetic properties mainly through interfacial effects [2,5,6,[10][11][12][13].…”

“…Moreover, this spin polarization depends on how strongly the molecules are linked to the surface. For instance, a spin polarization reversal due to the differing hybridization between Co-phthalocyanine molecules and each cobalt electrode has been evidenced in Co/CoPc/Co magnetic tunnel junctions [13]. Interface coupling was also found to strongly influence spin injection as demonstrated in the case of (La,Sr)MnO 3 /Alq 3 /Co magnetic tunnel junctions [1], or to stabilize an antiferromagnetic ordering at room temperature at the interface between a cobalt ferromagnetic layer and a paramagnetic organic manganese phthalocyanine (MnPc) layer [12].…”

“…Another emerging possibility is the coupling of a ferromagnet with organic molecules. Organic molecules can affect the surface magnetic properties mainly through interfacial effects [2,5,6,[10][11][12][13]. Currently, the achievable thickness of the ferromagnetic layers is thin enough, in nm range, to achieve enhancement of the magnetic properties through the interfacial interaction.…”

Magnetodielectric Response from Spin–Orbital Interaction Occurring at Interface of Ferromagnetic Co and Organometal Halide Perovskite Layers via Rashba Effect

“…Our earlier experimental studies have shown that the spins in ferromagnetic nanoparticles can interact with nearby orbital fields in organic molecules, generating spin–orbital interactions at the ferromagnetic/organic interface . Furthermore, using the ferromagnetic surface represents the most direct approach to inject spins into semiconductors, leading to a spin‐selective interface . In general, the spin‐selective interface requires the direct contact between a ferromagnet and an organic semiconductor by overlapping their orbital wave functions.…”

Recent progress in organic spintronics

“…Note that a recent study of spin-transport devices incorporating CoPc layers also shows the importance of ferromagnet/molecular orbital hybridization, e.g. giving rise to the new additional feature of large range control of the coercive field by the electric field [111].…”