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Key Inorganics for Spintronics and MagnetoElectrics

Periodic Reporting for period 1 - KISS ME (Key Inorganics for Spintronics and MagnetoElectrics)

Reporting period: 2017-09-01 to 2019-08-31

The control of electron spin and charge in materials is one major scientific quest with significant impact on society due to increasing needs for data storage densities. For instance, Giant Magneto Resistance (GMR) materials have application in magnetic hard drives that profoundly changed modern electronics. In the last years, multiferroic systems have attracted considerable attention due to the possibility of (cross-) controlling magnetization via the electric field (and respectively) with quite low power dissipation. However while multiferroics are often considered as the next breakthrough in spintronic technologies, it is admitted that all kinds of magneto-electric (ME) couplings are generally weak and exploitable multiferroic compounds are still rarities. The best candidates display to weak magneto-electric (ME) couplings (e.g. BiFeO3) or un-adapted working temperatures (e.g. TbMnO3) for extended multifunctionalities.
New materials and processes are then highly reclaimed to couple more efficiently magnetic and electric fields, rather than the improvement of known materials in which limitations are already stated. An enormous development of the theory was furnished in the last years, but so far focused on a very limited number of materials.
Due to the weak magnitude of the ME couplings and so rare candidates, it is the time now to think outside the box and imagine new guidelines towards efficient magnetoelectrics/multiferroics materials. Even without the coexistence of ferroic orders, the preliminary identification and quantification of the parameters responsible for strong magneto-electric effects will be an enormous progress with technological issues. For this, we propose original specific materials with strong ME effects and intrinsic multiferroic properties due to their unique crystallographic topologies, namely recent Low-D ferromagnets prepared at the UCCS and novel inspired ones. KISS-ME (Key Inorganic compounds for SpintronicS with exacerbate intrinsic Magneto-Electric potentialities) is focused on the design and characterisation of these promising compounds.
"The worked performed in the frame of “KISS-ME” can be organised as follows:

1) Career development and attracted funding.

In terms of career development, Angel M. Arevalo-Lopez has become a Chargé de Recherche at the CNRS in the same Institution where the project was held.

This project has also helped to attract more funding. For instance, the “STaRS - pour Soutien à l’accueil de talents de la recherche scientifique"" from the Region Hauts-de-France.

Taking KISS-ME as starting point, an ANR-JCJC project has also been approved by the French National Research Agency (ANR).

2) Equipment installation and development.

Along this project, a magneto-dielectric probe has been built. This consists of an inset for the Physical Properties Measurement System (PPMS from Quantum Design) that can incorporate an LCR meter along with the software to integrate both equipment. The advantage of this probe is that it can measure the dielectric properties of the desired material at low temperatures and high magnetic fields.

3) Research results:

Following the idea of “low-dimensional” structures for enhanced magnetism, we have discovered new phases, e.g. the novel KFe3Ge4O10(OH)2 mica related type, with FeO layers forming a triangular lattice and develop a ferrimagnetic structure below Tn = 56 K.

Another important development is on the BaCoAs2O7. This phase shows a very complex structure, with a P-1 structure and a structural modulation with q = (0.29 0.075 0.47). Neutron diffraction studies under magnetic field show the evolution from a well ordered antiferromagnetic structure with k = [1/2 0 0] into a spin density wave at 5.5 T that follows the same structural modulation i.e. q = k. At magnetic fields higher than 7 T, a transformation to a FM structure is observed. This phase has also shown multiferroic properties being in a centrosymmetric structure, which opens a new paradigm in multiferroicity: where a structurally modulated structure shows a commensurate spin structure in comparison with the well-known inverse Dzyaloshinskii-Moriya mechanism where a well ordered crystal structure shows a modulated spin structure.

We have also applied soft-chemistry techniques to study the BaNiO3 – BaNiO2 system. We have observed a series of modulated structures in between, with coexistence of Ni4+ octahedral and Ni2+ trigonal bi-prisms without any presence of Ni3+, these materials show NiO exsolution.

Four directly related scientific articles have been published within the frame of KISS-ME. Results related have also been presented at national and international level."
We have realised a new paradigm on multiferroic compounds, for type-II multiferroics, usually a well ordered structure presents a complex magnetic structure (e.g. cycloidal). However, in one of the compounds studied in here the opposite occurs, a complex modulated structure, presents a well ordered not-complex magnetic structure, which by symmetry arguments should not be multiferroic, although the coupling between magnetic and electric properties exist, posing a challenge for theoreticians. This is a very good progress beyond the state of the art and clearly opens up new ways to search for multiferroic materials in modulated structures.

Perhaps this is the strategy to follow in order to bring multiferroic compounds from a lab rarity to a useful technology.

Besides this, the search of multiferroic materials on metamagnetic compounds has also been fruitful an several compounds have been discovered and reported.
Synopsis of KISS-ME