scholarly journals An Ab Initio Study of Pressure-Induced Changes of Magnetism in Austenitic Stoichiometric Ni2MnSn

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 523
Author(s):  
Martin Friák ◽  
Martina Mazalová ◽  
Ilja Turek ◽  
Adéla Zemanová ◽  
Jiří Kaštil ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Magnetic State ◽  
Magnetic Moments ◽  
Qualitative And Quantitative ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
Similar Formation ◽  
Induced Changes ◽  
Formation Energies

We have performed a quantum-mechanical study of a series of stoichiometric Ni2MnSn structures focusing on pressure-induced changes in their magnetic properties. Motivated by the facts that (i) our calculations give the total magnetic moment of the defect-free stoichiometric Ni2MnSn higher than our experimental value by 12.8% and (ii) the magnetic state is predicted to be more sensitive to hydrostatic pressures than seen in our measurements, our study focused on the role of point defects, in particular Mn-Ni, Mn-Sn and Ni-Sn swaps in the stoichiometric Ni2MnSn. For most defect types we also compared states with both ferromagnetic (FM) and anti-ferromagnetic (AFM) coupling between (i) the swapped Mn atoms and (ii) those on the Mn sublattice. Our calculations show that the swapped Mn atoms can lead to magnetic moments nearly twice smaller than those in the defect-free Ni2MnSn. Further, the defect-containing states exhibit pressure-induced changes up to three times larger but also smaller than those in the defect-free Ni2MnSn. Importantly, we find both qualitative and quantitative differences in the pressure-induced changes of magnetic moments of individual atoms even for the same global magnetic state. Lastly, despite of the fact that the FM-coupled and AFM-coupled states have often very similar formation energies (the differences only amount to a few meV per atom), their structural and magnetic properties can be very different.

scholarly journals Impact of Antiphase Boundaries on Structural, Magnetic and Vibrational Properties of Fe3Al

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4884
Author(s):  
Martin Friák ◽  
Miroslav Černý ◽  
Monika Všianská ◽  
Mojmír Šob
Keyword(s):  
Magnetic Moments ◽  
Harmonic Approximation ◽  
Interface Energy ◽  
Vibrational Properties ◽  
Phonon Modes ◽  
Antiphase Boundaries ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
Lower Entropy ◽  
Induced Changes

We performed a quantum-mechanical study of the effect of antiphase boundaries (APBs) on structural, magnetic and vibrational properties of Fe3Al compound. The studied APBs have the {001} crystallographic orientation of their sharp interfaces and they are characterized by a 1/2⟨111⟩ shift of atomic planes. There are two types of APB interfaces formed by either two adjacent planes of Fe atoms or by two adjacent planes containing both Fe and Al atoms. The averaged APB interface energy is found to be 80 mJ/m2 and we estimate the APB interface energy of each of the two types of interfaces to be within the range of 40–120 mJ/m2. The studied APBs affect local magnetic moments of Fe atoms near the defects, increasing magnetic moments of FeII atoms by as much as 11.8% and reducing those of FeI atoms by up to 4%. When comparing phonons in the Fe3Al with and without APBs within the harmonic approximation, we find a very strong influence of APBs. In particular, we have found a significant reduction of gap in frequencies that separates phonon modes below 7.9 THz and above 9.2 THz in the defect-free Fe3Al. All the APBs-induced changes result in a higher free energy, lower entropy and partly also a lower harmonic phonon energy in Fe3Al with APBs when compared with those in the defect-free bulk Fe3Al.

scholarly journals A Quantum-Mechanical Study of Antiphase Boundaries in Ferromagnetic B2-Phase Fe2CoAl Alloy

2021 ◽  
Vol 7 (10) ◽  
pp. 137 ◽  
Author(s):  
Martin Friák ◽  
Josef Gracias ◽  
Jana Pavlů ◽  
Mojmír Šob
Keyword(s):  
Computational Models ◽  
Poisson Ratio ◽  
Magnetic Moments ◽  
Quantum Mechanical ◽  
Random Structure ◽  
Antiphase Boundaries ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
Similar Formation ◽  
Type Lattice

In this study, we performed a quantum mechanical examination of thermodynamic, structural, elastic, and magnetic properties of single-phase ferromagnetic Fe2CoAl with a chemically disordered B2-type lattice with and without antiphase boundaries (APBs) with (001) crystallographic orientation. Fe2CoAl was modeled using two different 54-atom supercells with atoms on the two B2 sublattices distributed according to the special quasi-random structure (SQS) concept. Both computational models exhibited very similar formation energies (−0.243 and −0.244 eV/atom), B2 structure lattice parameters (2.849 and 2.850 Å), magnetic moments (1.266 and 1.274 μB/atom), practically identical single-crystal elastic constants (C11 = 245 GPa, C12 = 141 GPa, and similar C44 = 132 GPa) and auxetic properties (the lowest Poisson ratio close to −0.1). The averaged APB interface energies were observed to be 199 and 310 mJ/m2 for the two models. The studied APBs increased the total magnetic moment by 6 and 8% due to a volumetric increase as well as local changes in the coordination of Fe atoms (their magnetic moments are reduced for increasing number of Al neighbors but increased by the presence of Co). The APBs also enhanced the auxetic properties.

scholarly journals A Quantum–Mechanical Study of Clean and Cr–Segregated Antiphase Boundaries in Fe3Al

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 3954 ◽  
Author(s):  
Martin Friák ◽  
Monika Všianská ◽  
Mojmír Šob
Keyword(s):  
Magnetic Properties ◽  
Magnetic Moments ◽  
Lattice Parameter ◽  
Quantum Mechanical ◽  
Strong Impact ◽  
Antiphase Boundaries ◽  
Cubic Symmetry ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
The Impact

We present a quantum-mechanical study of thermodynamic, structural, elastic, and magnetic properties of selected antiphase boundaries (APBs) in Fe 3 Al with the D0 3 crystal structure with and without Cr atoms. The computed APBs are sharp (not thermal), and they have {001} crystallographic orientation. They are characterized by a mutual shift of grains by 1/2⟨100⟩a where a is the lattice parameter of a cube-shaped 16-atom elementary cell of Fe 3 Al, i.e., they affect the next nearest neighbors (APB-NNN type, also called APB-D0 3 ). Regarding clean APBs in Fe 3 Al, the studied ones have only a very minor impact on the structural and magnetic properties, including local magnetic moments, and the APB energy is rather low, about 80 ± 25 mJ/m 2 . Interestingly, they have a rather strong impact on the anisotropic (tensorial) elastic properties with the APB-induced change from a cubic symmetry to a tetragonal one, which is sensitively reflected by the directional dependence of linear compressibility. The Cr atoms have a strong impact on magnetic properties and a complex influence on the energetics of APBs. In particular, the Cr atoms in Fe 3 Al exhibit clustering tendencies even in the presence of APBs and cause a transition from a ferromagnetic (Cr-free Fe 3 Al) into a ferrimagnetic state. The Fe atoms with Cr atoms in their first coordination shell have their local atomic magnetic moments reduced. This reduction is synergically enhanced (to the point when Fe atoms are turned non-magnetic) when the influence of clustering of Cr atoms is combined with APBs, which offer specific atomic environments not existing in the APB-free bulk Fe 3 Al. The impact of Cr atoms on APB energies in Fe 3 Al is found to be ambiguous, including reduction, having a negligible influence or increasing APB energies depending on the local atomic configuration of Cr atoms, as well as their concentration.

Electronic and Magnetic Properties of Ternary Stannides RERhSn (RE = Tb, Dy and Ho)

2011 ◽  
Vol 170 ◽  
pp. 74-77 ◽  
Author(s):  
Kazimierz Łątka ◽  
Jacek Gurgul ◽  
Andrzej W. Pacyna ◽  
Rainer Pöttgen
Keyword(s):  
Magnetic Properties ◽  
Electric Field ◽  
Magnetic Moment ◽  
Magnetic Moments ◽  
Magnetic Studies ◽  
Crystalline Electric Field ◽  
Electric Field Effects ◽  
Electronic And Magnetic Properties ◽  
Field Effects

The results of magnetic studies and Mössbauer investigations made with 119Sn source are reviewed for the series of RERhSn (RE = Tb, Dy and Ho) compounds crystallizing in the same hexagonal ZrNiAl-type of structure. The role of crystalline electric field effects in the establishing of magnetic moment orientations observed in these compounds and their influence on the observed magnitudes of magnetic moments are discussed.

scholarly journals Interatomic Forces and Bonding Mechanisms in MgO Clusters

1990 ◽  
Vol 193 ◽  
Author(s):  
Nancy F. Wright ◽  
Gayle S. Painter
Keyword(s):  
Interatomic Potentials ◽  
Many Body ◽  
Restoring Force ◽  
Mechanical Study ◽  
Quantum Mechanical Study ◽  
Force Curves ◽  
The Many ◽  
Quantum Treatment ◽  
Oxygen Ratio

ABSTRACTWe report results from a first-principles local spin density quantum mechanical study of the energetics and elastic properties of a series of magnesium-oxygen clusters of various morphologies. The role of quantum effects, e.g. covalency, in the bonding character of diatomic MgO is determined by comparison of classical and quantum restoring force curves. The dependence of binding properties on geometry and metal to oxygen ratio is determined by comparison of binding energy curves for a series of clusters. Results show that while gross features of the binding curves may be represented by simple interatomic potentials, details require the many body corrections of a full quantum treatment.

scholarly journals The role of intrinsic vacancy defects in the electronic and magnetic properties of Sr3SnO: a first-principles study

RSC Advances ◽  
2017 ◽  
Vol 7 (12) ◽  
pp. 6880-6888 ◽  
Author(s):  
Javaria Batool ◽  
Syed Muhammad Alay-e-Abbas ◽  
Adnan Ali ◽  
Khalid Mahmood ◽  
Shaheen Akhtar ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Stability Diagram ◽  
Vacancy Defects ◽  
Electronic And Magnetic Properties ◽  
O Vacancy ◽  
Formation Energies ◽  
Thermodynamic Stability Diagram

The thermodynamic stability diagram and formation energies of intrinsic vacancy defects in Sr3SnO. Sr and O vacancy containing Sr3SnO is non-magnetic, while ferromagnetism is achieved in Sn deficient Sr3SnO.

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