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NOVel, critical materials free, high Anisotropy phases for permanent MAGnets, by design.

Periodic Reporting for period 3 - NOVAMAG (NOVel, critical materials free, high Anisotropy phases for permanent MAGnets, by design.)

Reporting period: 2018-10-01 to 2019-09-30

The demand for lower dependency on critical raw materials (CRM) such as rare earths (RE) is not only a European but a global problem that demands immediate action. The purpose of this proposal is to exploit advanced theoretical and computation methods together with state-of-the-art materials preparation and characterization techniques, to develop the next generation RE-free/lean permanent magnets (PM). The material design will be driven by automated large computational screening of new and novel intermetallic compounds with uniaxial structure in order to achieve high saturation magnetisation, magnetocrystalline anisotropy and Curie temperature. The simulations will be based on a primary screening detecting the mechanisms that give rise to distorted phases and stabilize them, by adding doping atoms as stabilizers. In a further computation on successfully synthetized compounds, micromagnetic calculations will be used in order to design the optimal microstructure for the given phases that will maximise the coercivity needed for a PM. Extensive experimental processing and characterisation of the selected phases will result in a first proof of principle of the feasibility of NOVAMAG PMs. A multidisciplinary team of magnet experts consisting of chemists, material scientists, physicists and engineers from academia, national labs and industry is assembled to undertake a concerted, systematic and innovative study to overcome the problems involved and develop the next generation RE-free/lean PMs. Currently the demand for these PMs is even higher with the emerging markets of hybrid/electric vehicles and wind mill power systems. The proposed research and development will provide the fundamental innovations and breakthroughs which will have a major impact in re-establishing the Europe as a leader in the science, technology and commercialization of this very important class of materials and help decrease our dependence on China, which will in turn improve the competitiveness of EU manufacturers.
AGA methodology was applied to massively explore the crystal phase space of Fe-rich and Mn-Al phases searching for new non-cubic structures with high stability (negative enthalpy of formation, ∆HF<0) and high saturation magnetization (µ0MS>1T). From this massive exploration,around 12.000 structures, finding more tan 100 which could fulfil the first screening: deltaHf < 0; u0Ms > 1T; structure=HEX, TET, ORT, RHO, ferromagnetic structures were calculated by an initial quick estimation so we could select several compounds for the calculation of magnetic properties. This procedure was implemented into the AGA search in an efficient way. The structure of the candidate phases was further optimized.
The magnetic properties of the newly predicted phases and of known optimized phases identified in WP1 were studied by first principles methods. These magnetic properties comprise: magnetic moments, MAE, exchange coupling constants, Curie temperature, M(T), thermodynamics. Calculated magnetic properties of the new phases and known optimized phases, together with experimental data, are being included in a very comprehensive database that will be ready at the end of the project. We follow the European Material Modelling Ontology (EMMO) and construct the database taxonomy and ontology based on MODA.
A very wide and comprehensive experimental screening of the predicted phases has been carried out by several techniques: combinatorial sputtering, reactive crucible melting and non-equilibrium techniques, such as melt spinning or mechanical alloying. Among all the samples that were produced, some were already discarded. Some compounds, with very promising properties, have not been produced so far, but further efforts will be done.
The influence of the microstructure and temperature on the coercivity and maximum energy product were theoretically studied. Interface properties and grain boundary stability were studied by means of density functional theory (DFT) calculations and molecular dynamics simulations. Promising candidate phases for rare-earth free permanent magnets were studied with respect to interfaces and grain boundaries. In addition, spin dynamics simulations were used to compute the temperature dependence of the intrinsic magnetic properties and to calculate the influence of local anisotropy variations next to interfaces on coercivity.
The microstructure of a magnet is essential for developing coercivity. The influence of the microstructure on coercivity, remanence, and energy density product was studied using micromagnetic simulations. In these simulations synthetic microstructures were built and discretized with finite elements. Using numerical optimization tools, the structures were optimized, in order to maximize the coercive field or the energy density product. Structure optimization was performed for possible candidate phases. A study on the influence of thermal activation on the coercive field of permanent magnets made from candidate phases was also carried out.
A full structural, thermodynamic and magnetic characterization has been carried out in samples produced in WP3. Different characterization techniques provide information complementary to each other. The experimental results are compared with the predictions obtained by theoretical groups, so that they can adjust the models and computing methods with our input, to get a better understanding of the real behavior, and improve further predictions.
The AGA method has been implemented for massive exploration of the structures, and validated against known stable phases of representative magnetic structures. A 100% of success rate was obtained for predicting well-known representative magnetic structures, comprising intermetallic alloys, oxides, interstitial compounds and systems containing rare-earth elements, for both ferromagnetic and antiferromagnetic ordering.

TUDA performed systematic calculations on FeNi+X and FeCo+X (X=H, B, C and N) to study the induced tetragonal distortion. It has been observed that N tends to stabilize an enhanced tetragonal distortion of the FeNi lattice. Experimentally, NCRSD was able to obtain an important percentage of the tetragonal phase in bulk by flux melting with In. Actually, this important finding could be subject for a patent application, as industrial partners pointed in WP9. We expect to obtain an even larger percentage of the tetragonal phase by optimization of the synthesis techniques.

In the following months, we expect to produce bonded (Nd-based nitrogenated 1:12 alloys) and sintered magnets (Sm-based 1:12 alloys) and also by additive manufacturing (Mn-Al-C alloys). The magnetic properties of these magnets will be measured and we expect to obtain results that would be interesting for industries to produce and use our magnets. If successful results are obtained for these magnets we would have achieved a large reduction of the RE-content in PM and so CRM-content.

The database that we are currently designing and implementing would comprise very useful information for both theoreticians and experimentalists about not only structural but also magnetic properties of a very wide range of compounds. This database will be open for users so everyone can access and take advantage of our research.