Dr. Martin BOWEN
Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), France
"Oxide and organic tracks toward nanospintronics within solid-state devices"
Abstract
The field of spintronics has endeavoured, over the past 25+ years and across several materials science/ physics research tracks, to promote a current source that is highly spin-polarized at room temperature and that operates at the nanoscale. While the tracks of dilute magnetic semiconductors and half-metallic metals fail several of these criteria1, those of symmetry-filtering2 across inorganic tunnel barrier and organic spintronics3 appear poised to satisfy these criteria. This seminar will broach the nanospintronic potential of these two tracks, which are both expressed using solid-state tunneling devices.
To introduce the topic of organic spintronics, I will describe how the spin-polarized charge transfer at the interface between a ferromagnetic metal and a molecule generates novel properties such as high spin-polarization4 at room temperature1 (as a generic property5,6). This interface, also called an organic spinterface, can not only alter the magnetism of the ferromagnet7, but also stabilize molecular spin chains away from the interface at room temperature8. This leads, within solid-state nanojunctions, to a rich array of spintronic properties including high magnetoresistance and spin-flip excitations9. These results affirm the milestone of solid-state tunneling across a structurally ordered organic tunnel barrier, much as what took place for inorganic tunnelling spintronics over 15 years ago with the shift from amorphous AlOx to MgO2.
Progress on inorganic tunneling spintronics, while enriched through studies across transition metal oxide barriers10, was strongly bolstered by studies of Fe/MgO-class magnetic tunnel junctions (MTJs)2, with lateral sizes presently around 10nm11. We will describe how taking into account the electronic properties of oxygen vacancies within the MgO tunnel barrier can explain the concurrence of low barrier heights and high spintronic performance required for next-generation memory (STT-MRAM) and computing (artificial synapse) solutions12. We will in particular focus on double oxygen vacancies, which promote coherent tunneling and enable an ultimate lateral size of 2nm13.
After evoking the opportunities for quantum physics presented by these nano-objects within solid-states, I will end the seminar by evoking our synchrotron-based work to explore solid-state device operation. I will illustrate both a conventional materials-centric14, as well as a novel device-centric15, operando approach. The latter’s ability to probe a device’s active atoms alters research philosophy by enhancing the causality between materials science and device research, toward greater research efficiency.
References
1. Djeghloul, F. et al. Direct observation of a highly spin-polarized organic spinterface at room temperature. Sci. Rep. 3, 1272 (2013).
2. Miao, G.-X., Münzenberg, M. & Moodera, J. S. Tunneling path toward spintronics. Rep. Prog. Phys. 74, 36501 (2011).
3. Sanvito, S. & Dediu, V. A. Spintronics : News from the organic arena. Nat. Nanotechnol. 7, 696–697 (2012).
4. Barraud, C. et al. Unravelling the role of the interface for spin injection into organic semiconductors. Nat. Phys. 6, 615–620 (2010).
5. Djeghloul, F. et al. Highly spin-polarized carbon-based spinterfaces. Carbon 87, 269–274 (2015).
6. Djeghloul, F. et al. High Spin Polarization at Ferromagnetic Metal-Organic Interfaces : a Generic Property. J. Phys. Chem. Lett. 7, 2310–2315 (2016).
7. Raman, K. V. et al. Interface-engineered templates for molecular spin memory devices. Nature 493, 509–513 (2013).
8. Gruber, M. et al. Exchange bias and room-temperature magnetic order in molecular layers. Nat. Mater. 14, 981–984 (2015).
9. Barraud, C. et al. Phthalocyanine based molecular spintronic devices. Dalton Trans 45, 16694–16699 (2016).
10. Bowen, M. et al. Observation of Fowler–Nordheim hole tunneling across an electron tunnel junction due to total symmetry filtering. Phys. Rev. B 73, 140408(R) (2006).
11. Sato, H. et al. Properties of magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure down to junction diameter of 11 nm. Appl. Phys. Lett. 105, 62403 (2014).
12. Schleicher, F. et al. Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO. Nat. Commun. 5, 4547 (2014).
13. Taudul, B. et al. Tunneling Spintronics across MgO Driven by Double Oxygen Vacancies. Adv. Electron. Mater. 1600390 (2017). doi:10.1002/aelm.201600390
14. Studniarek, M. et al. Modulating the Ferromagnet/Molecule Spin Hybridization Using an Artificial Magnetoelectric. Adv. Funct. Mater. 1700259 (2017). doi:10.1002/adfm.201700259
15. Studniarek, M. et al. Probing a Device’s Active Atoms. Adv. Mater. 1606578 (2017). doi:10.1002/adma.201606578
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