An adaptive genetic algorithm approach for predicting magnet-ic structure suitable for high-performance permanent magnet development

Trabajo presentado en: International Conference on Magnetics (INTERMAG), 2017Summary form only given. In this work, we present a general overview, analysis and software implementation of a particular AGA, which has been proposed for discovering new RE-free magnetic crystal phases in the context of the EU-H2020 NOVAMAG project. The workflow diagram related to the Modelling Data Elements (MODA) of the magnetic crystal structure calculation based on AGA was shown. In particular, we make use of an AGA, implemented through USPEX and VASP codes, to predict new magnetic crystal phases, where those structures with better magnetic properties for a permanent magnet are selected and analyzed in more detail. Such a methodology has been preliminary compared to well-known experimentally reported properties compounds, showing an excellent agreement. In addition, we show recent results predicted by AGA in CoFe 2n X (n=1,2,3,4,5; where X=C, P, Hf, Zr, ...), where we found compounds with many metastable structures which fulfill the initial requirements (negative enthalpy of formation ΔHF1T and non-cubic lattice system) for permanent magnet development.NOVAMAG project, under Grant Agreement No. 686056, EU Horizon 2020 Framework Programme for Research and Innovation (2014-2020). Authors also acknowledge the Spanish Supercomputing Network (RES) and CESVIMA for providing supercomputational resources under Ref: QCM-2016-2-0034

Exploring the Crystal Structure Space of CoFe2P by Using Adaptive Genetic Algorithm Methods

Advances in theoretical and computational condensed matter physics have opened the possibility to predict and design magnetic materials for specific technological applications. In this paper, we use the adaptive-genetic algorithm technique for exploring the low-energy crystal structure configurations of Co0.25Fe0.5P0.25, aiming to find new low-energy non-cubic phases with high saturation magnetization that might be interesting for high-performance permanent magnet development.This work was supported in part by the NOVAMAG project under Grant 686056, in part by the EU Horizon 2020 Framework Program for Research and Innovation (2014–2020), and in part by the Spanish Supercomputing Network and CESVIMA for providing computational resources under Grant QCM-2016-2-0034

A high-throughput exploration of magnetic materials by using structure predicting methods

We study the capability of a structure predicting method based on genetic/evolutionary algorithm for a high-throughput exploration of magnetic materials. We use the USPEX and VASP codes to predict stable and generate low-energy meta-stable structures for a set of representative magnetic structures comprising intermetallic alloys, oxides, interstitial compounds, and systems containing rare-earths elements, and for both types of ferromagnetic and antiferromagnetic ordering. We have modified the interface between USPEX and VASP codes to improve the performance of structural optimization as well as to perform calculations in a high-throughput manner. We show that exploring the structure phase space with a structure predicting technique reveals large sets of low-energy metastable structures, which not only improve currently exiting databases, but also may provide understanding and solutions to stabilize and synthesize magnetic materials suitable for permanent magnet applications.EU H2020 Program Project NOVAMAG: Novel, critical materials free, high anisotropy phases for permanent magnets, by design (Project ID: 686056)

Atomistic spin dynamics simulations of the MnAl τ-phase and its antiphase boundary

In this work we develop an atomistic spin dynamics model for the ideal Mn 50 Al 50 τ -phase by means of first-principles calculations. The model is applied to study the domain wall and antiphase boundary phenomenology. In particular, it allows us to obtain the dependence on the interfacial exchange coupling of the nucleation and depinning fields, as well as the macroscopic magnetization profile across the antiphase boundary. We find that microscopic antiferromagnetic exchange coupling stronger than 10 meV could unavoidably lead to the formation of a domain wall at the antiphase boundary.European Horizon 2020 Framework Programme for Research and Innovation (2014- 2020) under Grant Agreement No. 686056, NOVAMAG

Computational design of rare-earth reduced permanent magnets

Multiscale simulation is a key research tool in the quest for new permanent magnets. Starting with first principles methods, a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition. Iron (Fe)-rich magnetic phases suitable for permanent magnets can be found by means of adaptive genetic algorithms. The intrinsic properties computed by ab intro simulations are used as input for micromagnetic simulations of the hysteresis properties of permanent magnets with a realistic structure. Using machine learning techniques, the magnet's structure can be optimized so that the upper limits for coercivity and energy density product for a given phase can be estimated. Structure property relations of synthetic permanent magnets were computed for several candidate hard magnetic phases. The following pairs (coercive field (T), energy density product (kJ.m(-3))) were obtained for iron-tin-antimony (Fe3Sn0.75Sb0.25): (0.49, 290), L1(0) -ordered iron-nickel (L1(0) FeNi): (1, 400), cobalt-iron-tantalum (CoFe6Ta): (0.87, 425), and manganese-aluminum (MnAl): (0.53, 80).Web of Science6215314

Applying high‐throughput computational techniques for discovering next‐generation of permanent magnets

The uncertainty in rare‐earth market resulted in worldwide efforts to develop rare‐earth‐lean/free permanent magnets. In this paper, we discuss about this problem and analyse how advances in computational and theoretical condensed matter physics could be essential in the development of a new generation of high‐performance permanent magnets via high‐throughput computational technique for material design. Additionally, we show that an adaptive genetic algorithm based methodology could be a useful tool for finding new magnetic phases. In particular, we apply such approach to Fe0.75Sn0.25 compound recovering well‐known experimental results and also finding new low‐energy magnetic metastable structuresNOVAMAG project, under Grant Agreement No. 686056, EU Horizon 2020 Framework Programme for Research and Innova-tion (2014-2020). Authors also acknowledge the Spanish Super-computing Network (RES) and CESVIMA for providing super-computational resources under Ref. QCM-2016-2-003

Database of novel magnetic materials for high-performance permanent magnet development

This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it contains significant results of novel magnetic phases with high magnetocrystalline anisotropy obtained by three computational high-throughput screening approaches based on a crystal structure prediction method using an Adaptive Genetic Algorithm, tetragonally distortion of cubic phases and tuning known phases by doping. Additionally, it also includes theoretical and experimental data about fundamental magnetic material properties such as magnetic moments, magnetocrystalline anisotropy energy, exchange parameters, Curie temperature, domain wall width, exchange stiffness, coercivity and maximum energy product, that can be used in the study and design of new promising high-performance Rare-Earth free/lean permanent magnets. The results therein contained might provide some insights into the ongoing debate about the theoretical performance limits beyond Rare-Earth based magnets. Finally, some general strategies are discussed to design possible experimental routes for exploring most promising theoretical novel materials found in the database.European Horizon 2020 Framework Programme for Research and Innovation (2014-2020) under Grant Agreement No. 686056, NOVAMAG. European Regional Development Fund in the IT4Innovations national supercomputing center – path to exascale project, project number CZ 02.1.01/0.0/0.0/16–013/0001791 within the Operational Programme Research, Development and Educatio

Understanding Physical Reality via Virtual Experiments

In this thesis I have studied some problems of condensed matter at high pressures and temperatures by means of numerical simulations based on Density Functional Theory (DFT). The stability of MgCO3 and CaCO3 carbonates at the Earth's mantle conditions may play an important role in the global carbon cycle through the subduction of the oceanic crust. By performing ab initio electronic structure calculations, we observed a new high-pressure phase transition within the Pmcn structure of CaCO3. This transformation is characterized by the change of the sp-hybridization state of carbon atom and indicates a change to a new crystal-chemical regime. By performing ab initio Molecular Dynamics simulations we show the new phase to be stable at 250 GPa and 1000K. Thus, the formation of sp3 hybridized bonds in carbonates can explain the stability of MaCO3 and CaCO3 at pressures corresponding to the Earth's lower mantle conditions. We have also calculated phase transition sequence in CaCO3, SrCO3 and BaCO3, and have found that, despite the fact that these carbonates are isostructural and undergo the same type of aragonite to post-aragonite transition, their phase transformation sequences are different at high pressures. The continuous improvement of the high-pressure technique led to the discovery of new composite structures at high pressures and complex phases of many elements in the periodic table have been determined as composite host-guest incommensurate structures. We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells and exploiting the fact that the total energy of the system is a function of structural parameters. By applying this method to the Sc-II phase, we have determined the incommensurate ratio, lattice parameters and Wyckoff positions of Sc-II in excellent agreement with the available experimental data. Moreover, we predict the occurrence of an incommensurate high-pressure phase in Ca from first-principle calculations within this approach. The implementation of DFT in modern electronic structure calculation methods proved to be very successful in predicting the physical properties of a solid at low temperature. One can rigorously describe the thermodynamics of a crystal via the collective excitation of the ionic lattice, and the ab initio calculations give an accurate phonon spectra in the quasi-harmonic approximation. Recently an elegant method to calculate phonon spectra at finite temperature in a self-consistent way by using first principles methods has been developed. Within the framework of self-consistent ab initio lattice dynamics approach (SCAILD) it is possible to reproduce the observed stable phonon spectra of high-temperature bcc phase of Ti, Zr and Hf with a good accuracy. We show that this method gives also a good description of the thermodynamics of hcp and bcc phases of Ti, Zr and Hf at high temperatures, and we provide a procedure for the correct estimation of the hcp to bcc phase transition temperature