An Organic Spin Valve Embedding a Self‐Assembled Monolayer of Organic Radicals

Abstract

merging classical and quantum behavior in a nanosized object. [1][2][3][4] From the applicative point of view, the use of magnetic molecules in spintronics can offer several advantages due to different aspects. On one side, molecular magnets have the functionality of carrying magnetic information down to the molecular size. This encourages the race toward miniaturization of magnetic devices as well as the exploitation of magnetic molecules for quantum computing, [5] although this solution is still hindered by the low working temperature. [6][7][8] On the other side, nonmagnetic molecular materials like organic semiconductors (OSCs) have been considered rather extensively during the past decade in the search for optimal combinations for prototypical devices in the area of spintronics technology, i.e., spin-valves. [9] The magnetoresistance in such devices, which consist of ferromagnetic metal electrodes sandwiching a semiconducting material, depends on the injection and transport of the spin through the semiconductor spacer. OSCs typically possess weak spin-orbit coupling and, because of this, they guarantee longer spin coherence time compared to both inorganic semiconductors and metals. In this context, different organic materials, such as pentacene [10] and tris(8-hydroxyquinoline) aluminium(III) (Alq 3 ) [11,12] and the gallium(III) analogue (Gaq 3 ), [13] have been employed in combination with several ferromagnetic metals, such as Fe and Co:TiO 2[10] or Co and La 0.7 Sr 0.3 MnO 3 (briefly termed LSMO). [11,12] The changes of physical properties of both the metal and organic molecule at the interface have also attracted great scientific interests, so that the ad hoc term spinterface [14,15] has been advanced to describe the topic. From the organic side the spinterface describes the spin filtering effects caused by the spin-dependent hybridization of the organic and metallic orbitals, leading to different interfacial broadening (and hence transmissivity) of the localized organic states for the two spin channels. [14] On the other hand, it has been shown both experimentally [16] and theoretically [17][18][19] that some organic molecules can affect the magnetic properties of the underlying magnetic surface, in terms of magnitude and direction of magnetic moments and spin polarization as well as of strength of exchange interactions. Moreover, coupling between the spins of transition-metal based molecular magnets and magnetic surfaces can be obtained promoting A novel functionalization of a ferromagnetic electrode employed in spintronic devices is reported. Self-assembling monolayer technique has been used to chemisorb a paramagnetic phosphonate functionalized nitronyl-nitroxide radical (NitPO) on the ferromagnetic La 0.7 Sr 0.3 MnO 3 (LSMO) manganite surface. This interfacial layer causes clearly detectable modifications of the behavior in prototypical LSMO/NitPO/Gaq 3 /AlOx/Co vertical spintronic devices at temperatures below the ferromagnetic alignment (estimated by density functional theory) of the magnetic mome...

Tuning of a Vertical Spin Valve with a Monolayer of Single Molecule Magnets

“…Figure a shows the square root of the MR versus T . The MR 1/2 ( T ) plot is linear in standard LSMO‐based spin valves (without additional functionalization), whose temperature dependence is mainly governed by LSMO surface spin polarization . While the ω‐iodo alkyl‐phosphonate set generally obeys this standard temperature dependence (red dots in Figure ), a clear deviation from linear behavior for T < 50 K is visible for samples with LSMO electrodes functionalized with the TbPc 2 (blue dots).…”

“…The deposition of Tb[Pc(PO 3 Et 2 )] 2 on LSMO has been achieved by implementing the same procedure previously described for the self‐assembly of nitronyl nitroxide radicals functionalized with the diethyl‐phosphonate group . In parallel, also the deposition of a ω‐iodo alkyl‐phosphonate, the diethyl(11‐iodoundecyl)phosphonate, has been performed to obtain a reference diamagnetic layer to be used in the following steps (see the Supporting Information for details).…”

“…In this context the wet chemistry‐based deposition of monolayer of magnetically bistable molecules, known as single molecule magnets (SMM), has been widely explored, evidencing suitable strategies for the stabilization or even the enhancement of the SMM behavior when these fragile complexes are chemisorbed on surface. We recently adopted a SAM‐based strategy to tune the LSMO interface by introducing a monolayer of chemisorbed organic radicals that alters the spin injection performances at low temperature through a spin‐filtering effect. Here, we aim to combine these concepts by developing a specific functionalization strategy to promote chemisorption of a modified terbium(III) double decker system, an archetypal SMM, on the LSMO surface.…”

Activating the molecular spinterface

“…Molecules that are farther away from the ferromagnetic surface-such as second-layer molecules-show a reduced hybridization strength, which can range from weak chemisorption to the physisorption regime, depending mostly on the geometric configuration of the specific interface. The same considerations also hold for molecules in direct contact with less reactive magnetic surfaces, such as oxygen-passivized surfaces and magnetic oxides [51][52][53] . We can thus Exemplification of the interactions at a molecular interface consisting of a transition metal (TM) surface and two layers of organic molecules.…”

Hybrid Interfaces in Molecular Spintronics

“…Self‐assembly of phosphonic acids on LSMO has also been recently extended to the fabrication of SVs with covalently immobilized polymer brushes with an improvement in the polymer/LSMO interface in comparison with spin‐coated films . This approach has also permitted the incorporation of SAMs containing organic radicals and single molecule magnets onto LSMO as intermediate layer between the ferromagnetic electrode and a semiconducting Gaq 3 layer (so these devices should be included as examples of group (i)).…”