Spin electronics, which operates thanks to the quantum electron spin property, can be downscaled to just a few nm and already benefits from industrial penetration in the information and communication technologies (ICT; read heads for hard drives; robust, non-volatile, ultrafast memories; bio-inspired computing…). Spintronics thus embodies a promising technological axis to implement industrial applications of quantum physics based on the spin and orbital symmetry of the electron.
The ‘Hybrid Spintronics’ team works on integrating quantum nanoobjects within spintronic devices, toward ICT and energy applications (see www.spinengine.tech). These nanoobjects are functional molecules, or even oxygen vacancies within the device’s tunnel barrier. This requires A) fundamental studies, for example into the emergent properties at the ferromagnetic metal/molecule interface, and B) technical advances beyond the state-of-the-art.
To do so, the team develops and operates an innovative research chain that comprises:
1) tools to grow and characterize metal/molecule heterostructures;
2) micro- and nano-technologies to make hybrid spintronic devices (partly using the STNano technological platform);
3) electrical measurements benches under external stimuli (temperature, magnetic field, light). The team also uses synchrotron radiation to probe the electronic properties of these heterostructures, and to test devices in operando.
Integrating functional spacers, such as the ferroelectric property of molecules, into spintronic devices is a means of achieving a multifunctional device, i.e. a device whose state (e.g. resistance) depends on a history of external stimuli (electric field, light, temperature, magnetic field, etc…). This targets Information and Communication Technologies.
Our team is developping a new method to harvest the thermal fluctuations of ambient temperature using spintronics. Our devices integrate the paramagnetic centers of oxide and molecular compounds into spintronic devices that also comprise electrodes that select a spin channel for transport. This latter feature is accomplished using so-called spinterfaces (see below). See www.spinengine.tech for more details.
In the news
We developed a novel nanotechnological process to study spin-polarized transport across a molecular spin chain within a solid-state device. Electrically exciting the spin chain from its quantum ground state generates a specific magnetoresistance signal. This quantum encoding of information lays the groundwork for information transmission across the spin chain. Adv. Func. Mater. 2009467 (2021). Savoir Magazine
The website www.spinengine.tech describes the concept to spintronically harvest thermal fluctuations to the academic and general publics.
We reported spontaneous electrical power generation from a single spintronic device at room temperature. In this ‘spin engine’, the thermal fluctuations of paramagnetic centers are spintronically harvested. In the process, we demonstrated that the current flowing across the ‘spinterface’ is highly spin-polarized. Commun. Phys., 2 116 (2019). CNRS News. , Unistra News. , www.spinengine.tech
We factually demonstrated that the spin crossover molecular property is involved in electrical transport, thanks to synchrotron-grade in operando experiments. ACS Appl. Mater. & Int., 10 31580 (2018). Soleil Highlight 2018.
The interface between a ferromagnet a molecule can develop emergent properties that are nicknamed the ‘spinterface’. The spinterface exhibits a low density of highly localized and highly spin-polarized electronic states at the Fermi level. We recently demonstrated that the current flowing across the spinterface is highly spin-polarized at room temperature. Thanks to these properties, the spinterface constitutes an essential building block to address the quantum spin states of other nano-objects within our spintronic devices.
Molecular spin chains
The formation of the spinterface can modify the electronic properties of the metal and molecule constituents. A ferromagnetic metal may see its magnetic anisotropy radically altered. A non-magnetic metal can become magnetic. The magnetization of the molecular interfacial layer can be extended into the molecular film by harnessing magnetic interactions between molecules. This allows the spinterface to stabilize the magnetization of paramagnetic spin chains borne by molecules. Here, we use planar phthalocyanine molecules with a central paramagnetic site. We are studying how to spintronically address the ground and excited states of these spin chains using molecular nanojunctions. These molecules are also used to study the spintronic harvesting of thermal fluctuations.
Spin crossover molecules
The central magnetic site of a spin crossover molecule can be switched from a low-spin to a high-spin electronic configuration using external stimuli (light, temperature, electric field…). This makes it a promising candidate to control a spintronic device’s performance. We demonstrated that this molecular functionality is factually involved in transport using a synchrotron-based operando experiment. The next step is to integrate this molecular class into spintronic nanojunctions. To do so, we are leveraging fundamental research (here and here) on achieving spinterfaces with a noble metal surface so as to not freeze the spin crossover molecular property.
Since spin-polarized charge transfer underscores the formation of the spinterface, one may modify the spinterface properties using ferroelectric molecules. To increase this effect, our team is optimizing the structural properties of the spinterface using croconic acid molecules, and intends to integrate these spinterfaces within spintronic nanojunctions. This method of forming an artificial magnetoelectric resembles efforts in the correlated oxides community, but benefits from a large charge transfer that is localized at the interface, and obviates the need to consider the role of oxygen vacancy migration.
Oxygen vacancies & paramagnetic centers
Controlling oxygen vacancies in functional oxides toward next-generation electronics remains challenging. Our team is examining how oxygen vacancies in the ‘simple’ oxide MgO drive the spintronic performance of magnetic tunnel junctions. Our experimental and theoretical results indicate that single and double oxygen vacancies can explain the combination of high spintronic performance, low barrier heights and metallic conduction depending on the junction’s magnetic state. We are examining the impact of these nano-objects on spin-transfer torque, a linchpin physical effect for spintronic technologies. Filling these vacancies with C can promote paramagnetic centers, leading to spintronic energy harvesting.
Along the research chain: from growth & characterization to device processing to multifunctional measurements
Growth & Characterization
Hybrid multichamber cluster
Ultra-high vacuum (UHV) tool to deposit metal, molecules and oxides using sputtering and thermal evaporation. Heterostructure stacks used to make nanojunctions are grown here.
Multiprobe UHV station
Variable temperature Omicron UHV setup to perform local probe techniques (AFM, conducting AFM, MFM, PFM, STM) on surface and bilayers. Basic spinterface studies are performed here. A UHV interconnect with the ‘Hybrid’ is underway.
Spin-polarized electron reflectometry
A UHV setup to probe the spin-polarized electronic properties of single films and heterostructures. Basic spinterface studies are performed here.
Our team has the expertise to conduct synchrotron beamtime runs in which in-situ grown heterostructures are probed using x-Ray absorption, spin-polarized photoemission and STXM.
The team implements a resist- and solvent-based process to craft heterostructures into ~10-micron diameter pillars for magnetotransport measurements. The process is compatible with correlated oxides.
Since most molecules may degrade under exposure to solvents and resist, our team has developed a resist- and solvent-free technology that crafts entire heterostructures (thereby preserving UHV-quality interfaces) into vertical nanojunctions. This is a unique capability world-wide.
Our team has developed an electrical transport bench around a cryo-free cryostat with the following characteristics: T:10-350K, up to H=2T along or at an angle with the sample and the optical axis, cw and ns-pulsed lasers covering 200-2600nm; ns-resolved spectroscopic camera, ns-grade electrical signal/response.
V2TI electrical insert at Beamline DEIMOS, Synchrotron SOLEIL
Our team helped to develop an electrical insert on Beamline DEIMOS, Synchrotron SOLEIL. It is therefore possible to implement the chemical and magnetic sensitivity of X-ray absorption spectroscopy (XAS) on materials subjected to electrical polling (e.g. spinterfaces), or even on devices in operando.
Eric Beaurepaire, décédé en Avril 2018.
Jacek Arabski, retraite en 2020.
DJ Kim, Postdoc at U. Warwick
S. Shi, postdoc at U. Linkoping
R. Rakshit, Scientist at CSIR-National Physical Laboratory, India
S. Javaid, Researcher at Pakistan Institute of Nuclear Science & Technology
JB Beaufrand, private sector
F. Schleicher, engineer at IMEC
H. Jabbar, professor at U. Basrah, Iraq
V. Davesne, private sector
M. Gruber, researcher at U. Kiel, Germany
U. Halisdemir, postdoc at U. Twente, Netherlands
M. Studniarek, private sector
E. Urbain, private sector
K. Katcko, an engineer at IMEC
B. Chowrira, engineer at IMEC
L. Kandpal, postdoc Muduli group, New Delhi
– 04/2012 : SOURCE DE COURANT POLARISEE EN SPINS, M. Bowen, W. Weber, L. Joly, E. Beaurepaire, F. Scheurer, S. Boukari, M. Alouani, FR 2012/ 12 53564 & PCT/EP2013/057804 & WO2013156441A1.
– 04/2012 : DISPOSITIF INJECTEUR DE SPINS COMPORTANT UNE COUCHE DE PROTECTION EN SON CENTRE, M. Bowen, M. Alouani, S. Boukari, E. Beaurepaire, W. Weber, F. Scheurer, L. Joly, FR 2012/ 12 53569 & PCT/EP2013/057769 & WO2013156426A1.
– 11/2012 : KIT DE CONNEXION D’UN COMPOSANT MICROELECTRONIQUE CONTRE DES DECHARGES ELECTROSTATIQUES LORS DE SA CONNEXION A UN DISPOSITIF CONDUCTEUR, M. Bowen, B. Leconte, D. Spor, FR 2012/12 60606 & PCT/ EP2013073174 & WO2014072347 A1.
– 11/2012 : DISPOSITIF DE POMPAGE, COMPRENANT UN ENSEMBLE DE POMPES EN SERIES ET UN ELEMENT DE COMMUTATION COMMUN, M. Bowen, C. Kieber, S. Boukari, FR 2012/12 60672 & PCT/ EP2013073344 & WO2014072452A1.
– 08/2014: PROCESS OF DETECTION OF LIGHT AND ASSOCIATED DEVICE, M. Bowen, U. Halisdemir, F. Schleicher, S. Boukari, E. Beaurepaire, EP14180354 & EP 2982950 A1 & WO2016020243A1.
Recent publications :