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(Multi)functional material growth and design

Functional scalability refers to the capability to enhance a system by simply the addition of new functionalities with least effort and resource. This scalability can be "horizontal" by adding multiple units processing the work as a single entity or "vertical" by adding a resource to a single unit to increase its ability. Thus, the concept of scalability is one of the major challenges for information technology, manipulation and data collection, especially in the case of spin electronics. However, this evolution towards systems with multiple functionalities requires the synthesis of new materials or new architectures, for which the understanding of the relationship between structure and properties represents an exciting playground for fundamental research issue and meets the future technology requirement.

 

Upstream of the nano-devices produced by our research group, the topic (Multi)functional material growth and design brings together the new strategies of synthesis, design and study of the properties of new materials. Several approaches will be at the heart of our future studies:
     

      -    Nature of compounds/composition
      -    Strain effects
      -    Interface engineering and symmetry
      -    Oxygen vacancy engineering.

 

 

These approaches will be used to tailor the physical properties, to bring about new functionalities and to combine/couple several properties (in particular for innovative barriers for the tunnel transport of electron, a strong competence of our research group). Recently, the search for combining several functionalities is as a fertile and competitive field in material science.

 

Among these materials, transition metal oxides owing to their versatility and their wide range of physical properties form a class of compounds with a high potential for functional scalability. The characteristic features of these materials are, on the one hand, strong electron correlations that consists in the interactions between the different degrees of freedom of the electron (spin, orbital, and charge) and the development of ordered phases (order of charge, orbital, electrical polarization, magnetization). Moreover, they are extremely sensitive to external excitations (electrical, magnetic, optical and stress). Thus, we will investigate the oxides that exhibit a perovskite structure (ABO3, A = rare earth or alkaline-earth metals, B = transition metal 3d, 4d or 5d) and in particular for RVO3 compounds. We will study the spin-orbital-structure interactions through the role of epitaxial, chemical constraints and oxygen deficiencies (or F-centers). The latter will also be studied in the case of MgO tunnel barriers for which we have shown the significant role of spin-polarized tunnel transport. Understanding the role of these oxygen vacancies on phenomena involving tunnel transport through MgO barriers is a direction that will be explored also by looking at the density profile, the types of vacancies in the barrier. Furthermore, the contribution of oxide materials to the other topics of our research group will also appear in the case of studies of the phenomena of manipulation of the magnetization by Spin Orbit Torque and All Optical Switching. We will be interested in the integration of ultra-thin ferrimagnetic and insulating layers (e.g. Y3Fe5O12) in different nano-devices. The study of these systems is nowadays a major topic of the spin electronics, also addressed in the Transport in Magnetic Systems topic.

 

 

Other interesting materials for spin electronics will also be studied. Among them, the magnetic half-metals whose particular electronic structure combines a metallic behavior for the majority spins and insulators for the minority spins. In particular, this is the case for the Heusler Co2MnSi alloy that we have recently characterized by spin-resolved photoemission. We propose to study the Heusler alloys more deeply by designing a magnetization perpendicular to the layers that we will exploit in devices Spin Transfer Torque devices (spin valve and tunnel junctions).

 

The search for new functionalities will also be related to inorganic and organic semiconductor materials. Thus, we will focus on the optical detection, in GaAs, Si and Ge, of electrically injected spins from ultrafine CoFeB/MgO films. In particular, long-spin transport in Si (low spin-orbit interaction), combined with the electrical control of spin orientation in SiGe, will be explored. Then, the organic materials will be studied from the point of view of their multifunctional properties and their interactions with magnetic, electrical and optical excitations .

 

Different deposition techniques will be used, adapted to the studied and combined materials: Atomic Layer deposition (ALD), Molecular Beam Epitaxy (MBE), Pulsed Laser Deposition (PLD) and Physical Vapor Deposition (PVD). All are connected to the ultra-high vacuum “tube” installed at Institut Jean Lamour. The relationship between structures and properties will be characterized by the techniques available at the Institut Jean Lamour and the regular experiments conducted by the group members on large facilities (synchrotron, neutrons).

 

 

Publications :

[1] Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO.
F. Shleicher et al., Nature Communications 5, 4547 (2014).

[2] Ferroelectric Control of Organic/Ferromagnetic Spinterface.
S.H. Liang et al., Advanced Materials, doi: 10.1002/adma.201603638 (2016).

[3] Interface magnetic anisotropy modified by electric field in epitaxial Fe/MgO(001)/Fe magnetic tunnel junction.
 A. Rajanikanth et al. , Appl. Phys. Lett. 103, 062402 (2013).

[4] Direct evidence for minority spin gap in the Co2MnSi Heusler alloy.

 

  S. Andrieu et al., Phys. Rev. B 93, 094417 (2016).