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.
