Interface-engineered templates for molecular spin memory devices

Abstract

The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices 1, 2 , opening avenues for developing multifunctional molecular spintronics 3 . Such ideas have been researched extensively, using singlemolecule magnets 4, 5 and molecules with a metal ion 6 or nitrogen vacancy 7 as localized spin-carrying centres for storage and for realizing logic operations 8 . However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task 9 . In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl 10 , have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli 11, 12 (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets 13 . Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.The diversity and flexibility of molecular synthesis has given researchers ample freedom to design functional molecules for spintronics. These include molecular magnets 14 , spinfilter molecules 15 , spin-crossover molecules 16 , molecular batteries 17 , molecular conductors 10 , molecular switches 12 , and spacer layers for organic spin valves 18 and magnetic tunnel junctions 19,20 . Using such synthetic techniques, we have designed a neutral planar phenalenyl-based molecule, zinc methyl phenalenyl (ZMP, C 14 H 10 O 2 Zn; see Fig. 1a and Methods), that has no net spin. When these molecules are grown on a ferromagnetic surface, interface spin transfer causes a hybridized organometallic supramolecular magnetic layer to develop, which shows a large magnetic anisotropy and spin-filter properties 21 . This interface layer creates a spin-dependent resistance and gives rise to an interface magnetoresistance (IMR) effect.

Room-temperature air-stable spin transport in bathocuproine-based spin valves

“…First, the temperature dependence of the resistance of most organic SVs is weak [7][8][9][10][11][12][13][14][15][16][17] , resembling more the behaviour of a tunnel junction than the temperature-activated transport typical of organic films 21 . Therefore, the question rises whether the SVs are actually probing the properties of the organics, or they are prone to artifacts coming from the interpenetration of the top metal contact into the organic layer.…”

“…Their spin-scattering mechanisms are extremely weak, and ultrahigh spin lifetimes (in the ms range) have been measured 6 . Organic spintronics is now an active research field, and different molecules have been used as interlayers in SV-like structures [7][8][9][10][11][12][13][14][15] . The measurement of MR in these devices is taken as the demonstration of the spin transport across the organic layer, which in some cases is very thick 7,9 (4100 nm).…”

“…Furthermore, reaction at a molecule/FM interface can result in interfacial states 19,20 with modified energetics and spin polarization. These new states are crucial for the operation of devices, as they can cause inversion or enhancement of MR 12 , as well as form FM organometallic compounds that behave as spin filters 15 .…”

FeCoCp3 Molecular Magnets as Spin Filters

“…4 Molecules can become fundamental pieces of the ever shrinking device technology. 5 Additionally, molecules show a great diversity of magnetic properties that can be successfully tailored, such as spin-crossover molecules, 6 molecular magnets, 3 spin-filtering molecules, 7 molecular spin valves 8 and molecular switches. 7 Molecular spintronics is then a rich field which promises scientific and technological breakthroughs.…”

Of interfaces and spin transport across nanoscale layers

“…Novel devices are envisioned that use injection and [134,135,136,162,163]. Similar effects have been observed in zinc methyl phenalenyl (ZMP) layers sandwiched between a FM electrode and a non-magnetic electrode, where the spin valve effect has been attributed to the special characteristics of the molecule/FM interface layer [164]. 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].…”