Temperature driven α\alpha to β\beta phase-transformation in Ti, Zr and Hf from first principles theory combined with lattice dynamics

Lattice dynamical methods used to predict phase transformations in crystals typically deal with harmonic phonon spectra and are therefore not applicable in important situations where one of the competing crystal structures is unstable in the harmonic approximation, such as the bcc structure involved in the hcp to bcc martensitic phase transformation in Ti, Zr and Hf. Here we present an expression for the free energy that does not suffer from such shortcomings, and we show by self consistent {\it ab initio} lattice dynamical calculations (SCAILD), that the critical temperature for the hcp to bcc phase transformation in Ti, Zr and Hf, can be effectively calculated from the free energy difference between the two phases. This opens up the possibility to study quantitatively, from first principles theory, temperature induced phase transitions.Comment: 4 pages, 3 figure

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)

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

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

Rare cause of recurrent pneumonia in the same site

Disciplina pneumologie și alergologie, Departamentul medicină internă, Universitatea de Stat de Medicină și Farmacie „Nicolae Testemiţanu”, Chișinău, Republica Moldova, Institutul de Ftiziopneumologie „Chiril Draganiuc”, Chișinău, Republica Moldov