Impact of Disorder on Properties of Vacancies: A Case Study of B2 and A2 Polymorphs of Non-Stoichiometric Fe2CoAl

Martin Friák; Jana Pavlů; Mojmír Šob

doi:10.3390/cryst11101207

Impact of Disorder on Properties of Vacancies: A Case Study of B2 and A2 Polymorphs of Non-Stoichiometric Fe2CoAl

Crystals ◽

10.3390/cryst11101207 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1207

Author(s):

Martin Friák ◽

Jana Pavlů ◽

Mojmír Šob

Keyword(s):

Magnetic Moment ◽

Single Phase ◽

Local Magnetic Moment ◽

Random Structure ◽

Ab Initio Study ◽

B2 Phase ◽

Structural And Magnetic Properties ◽

Induced Changes ◽

Formation Energies

We have performed an ab initio study of vacancy-induced changes in thermodynamic, structural and magnetic properties of single-phase ferromagnetic Fe2CoAl with a chemically disordered (i) two-sublattice B2 phase or (ii) single-sublattice A2 phase. The two polymorphs of slightly non-stoichiometric Fe2CoAl (Fe27Co14Al13) were modeled by two different 54-atom supercells with atoms distributed according to the special quasi-random structure (SQS) concept. Both the lower-energy B2 phase and a higher-energy A2 phase possess elastic constants that correspond to an auxetic material that is mechanically stable. The properties of vacancies were computed by systematically removing different atoms (one at a time) from the supercells and quite wide ranges of values of vacancy-related characteristics were obtained. The increase in the level of disorder (when changing from the B2 to the A2 phase) results in an increase in the scatter of calculated values. The Fe and Co vacancies have lower vacancy formation energies than the Al ones. The total magnetic moment of the supercell decreases when introducing Fe and Co vacancies but it increases due to Al ones. The latter findings can be partly explained by an increase of the local magnetic moment of Fe atoms when the number of Al atoms in the first neighbor shell of Fe atoms is reduced, such as due to Al vacancies.

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An Ab Initio Study of Magnetism in Disordered Fe-Al Alloys with Thermal Antiphase Boundaries

Nanomaterials ◽

10.3390/nano10010044 ◽

2019 ◽

Vol 10 (1) ◽

pp. 44

Author(s):

Martin Friák ◽

Miroslav Golian ◽

David Holec ◽

Nikola Koutná ◽

Mojmír Šob

Keyword(s):

Magnetic Moment ◽

Nearest Neighbor ◽

Computational Study ◽

Magnetic Moments ◽

Magnetic Flux Density ◽

Random Structure ◽

Antiphase Boundaries ◽

Thermally Induced ◽

B2 Phase ◽

Experimental Findings

We have performed a quantum-mechanical study of a B2 phase of Fe 70 Al 30 alloy with and without antiphase boundaries (APBs) with the {001} crystallographic orientation of APB interfaces. We used a supercell approach with the atoms distributed according to the special quasi-random structure (SQS) concept. Our study was motivated by experimental findings by Murakami et al. (Nature Comm. 5 (2014) 4133) who reported significantly higher magnetic flux density from A2-phase interlayers at the thermally-induced APBs in Fe 70 Al 30 and suggested that the ferromagnetism is stabilized by the disorder in the A2 phase. Our computational study of sharp APBs (without any A2-phase interlayer) indicates that they have moderate APB energies (≈0.1 J/m 2 ) and cannot explain the experimentally detected increase in the ferromagnetism because they often induce a ferro-to-ferrimagnetic transition. When studying thermal APBs, we introduce a few atomic layers of A2 phase of Fe 70 Al 30 into the interface of sharp APBs. The averaged computed magnetic moment of Fe atoms in the whole B2/A2 nanocomposite is then increased by 11.5% w.r.t. the B2 phase. The A2 phase itself (treated separately as a bulk) has the total magnetic moment even higher, by 17.5%, and this increase also applies if the A2 phase at APBs is sufficiently thick (the experimental value is 2–3 nm). We link the changes in the magnetism to the facts that (i) the Al atoms in the first nearest neighbor (1NN) shell of Fe atoms nonlinearly reduce their magnetic moments and (ii) there are on average less Al atoms in the 1NN shell of Fe atoms in the A2 phase. These effects synergically combine with the influence of APBs which provide local atomic configurations not existing in an APB-free bulk. The identified mechanism of increasing the magnetic properties by introducing APBs with disordered phases can be used as a designing principle when developing new magnetic materials.

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Fano-shaped impurity spectral density, electric-field-induced in-gap state, and local magnetic moment of an adatom on trilayer graphene

Physical Review B ◽

10.1103/physrevb.96.075410 ◽

2017 ◽

Vol 96 (7) ◽

Cited By ~ 1

Author(s):

Zu-Quan Zhang ◽

Shuai Li ◽

Jing-Tao Lü ◽

Jin-Hua Gao

Keyword(s):

Electric Field ◽

Spectral Density ◽

Magnetic Moment ◽

Local Magnetic Moment ◽

State And Local ◽

Trilayer Graphene ◽

Gap State

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First-Principles Study of the Local Magnetic Moment on a N-Doped Cu 2 O (111) Surface

Chinese Physics Letters ◽

10.1088/0256-307x/28/12/127102 ◽

2011 ◽

Vol 28 (12) ◽

pp. 127102 ◽

Cited By ~ 1

Author(s):

Zhi Wang

Keyword(s):

Magnetic Moment ◽

First Principles ◽

Local Magnetic Moment ◽

First Principles Study

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Residual Magnetic Moment Influences the Features of Fe3s XPS Spectrum: A Case Study

Current Materials Science ◽

10.2174/2666145415666211228115336 ◽

2021 ◽

Vol 15 ◽

Author(s):

Ranjan K Sahu

Keyword(s):

Magnetic Moment ◽

Magnetic Domain ◽

Anomalous Behavior ◽

Spectral Features ◽

Different Temperatures ◽

Magnetic Origin ◽

Xps Study ◽

Increasing Temperature ◽

Curie Temperature Tc

Background: Fe 3sXPS spectrumexhibits doublet peak instead of predicted singlet peak based on spin-orbit coupling theory. This anomalous behavior is considered to be magnetic origin. However, the effect of residual magnetic moment to the features of Fe3s doublet peakis not understood fully. Objective: This study aims to verify the effect of residual magnetic moment on the spectral features of Fe3s XPS spectrum of magnetic material. Method: As a case study, we have carried out a high temperature XPS study of the Fe 3s spectrum of magnetic domain aligned (MDA) sample with composition composed of SrFe10.8Al1.2O19. In addition, the XPS data have been compared with the data acquired at different temperatures of magnetic domain non-aligned (MDNA) sample. Results: The results show that the majority peak intensity and minority peak width of Fe 3s spectrum of MDA are smaller than those of the MDNA sample, and they increase systematically with increasing temperature. However, it is noted that the features of Fe3s spectrum of both MDA and MDNA samples are completely overlapped near and above the Curie temperature, Tc ~ 670K. Conclusion: The analysis of XPS data suggests that the residual magnetic moment influences the spectral features of Fe3s spectrum. These results provide evidences that it is important to consider the contribution of residual magnetic moment while deriving information from Fe 3s XPS spectrum of MDA sample.

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Windings Design for Single-phase Induction Motors Base on 4-phase Induction Motor (Case study: identical windings design)

MATEC Web of Conferences ◽

10.1051/matecconf/201821501023 ◽

2018 ◽

Vol 215 ◽

pp. 01023 ◽

Cited By ~ 1

Author(s):

Zuriman Anthony ◽

Erhaneli Erhaneli ◽

Zulkarnaini Zulkarnaini

Keyword(s):

Induction Motor ◽

Power Factor ◽

Single Phase ◽

Induction Motors ◽

Three Phase ◽

Motor Design

A 1-phase induction motor usually has a complicated windings design which compares to polyphase induction motor. In addition, a large capacitor start is required to operate the motor. It is an expensive way to operate the motor if it compare to polyphase induction motor. So, a new innovation method is required to make the motor more simple and cheaper. This research is purposed to study a new winding design for a single-phase capacitor motor. Winding design of the motor was conducted to a simple winding design like a 4-phase induction motor that has four identical windings. The comparator motor that use in this study was a Three-phase induction motor with data 1400 RPM, 1.5 HP, 50Hz, 380/220V, Y/Δ, 2.74/4.7A, 4 poles, that had the same current rating which the proposed method. The result showed that the motor design on this proposed method could be operated at 88.18 % power rating with power factor close to unity.

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Origin of the Low Magnetic Moment in Fe2AlTi: An Ab Initio Study

Materials ◽

10.3390/ma11091732 ◽

2018 ◽

Vol 11 (9) ◽

pp. 1732 ◽

Cited By ~ 9

Author(s):

Martin Friák ◽

Anton Slávik ◽

Ivana Miháliková ◽

David Holec ◽

Monika Všianská ◽

...

Keyword(s):

Ab Initio ◽

Magnetic Moment ◽

Energy Surface ◽

Magnetic Moments ◽

Local Magnetic Moment ◽

Spin Configuration ◽

Spin Effects ◽

Order Of Magnitude ◽

Huge Impact ◽

Insight Into

The intermetallic compound Fe 2 AlTi (alternatively Fe 2 TiAl) is an important phase in the ternary Fe-Al-Ti phase diagram. Previous theoretical studies showed a large discrepancy of approximately an order of magnitude between the ab initio computed magnetic moments and the experimentally measured ones. To unravel the source of this discrepancy, we analyze how various mechanisms present in realistic materials such as residual strain effects or deviations from stoichiometry affect magnetism. Since in spin-unconstrained calculations the system always evolves to the spin configuration which represents a local or global minimum in the total energy surface, finite temperature spin effects are not well described. We therefore turn the investigation around and use constrained spin calculations, fixing the global magnetic moment. This approach provides direct insight into local and global energy minima (reflecting metastable and stable spin phases) as well as the curvature of the energy surface, which correlates with the magnetic entropy and thus the magnetic configuration space accessible at finite temperatures. Based on this approach, we show that deviations from stoichiometry have a huge impact on the local magnetic moment and can explain the experimentally observed low magnetic moments.

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Stability and local magnetic moment of bilayer graphene by intercalation: first principles study

RSC Advances ◽

10.1039/c8ra03343a ◽

2018 ◽

Vol 8 (35) ◽

pp. 19732-19738 ◽

Cited By ~ 4

Author(s):

Jinsen Han ◽

Dongdong Kang ◽

Jiayu Dai

Keyword(s):

Magnetic Properties ◽

Magnetic Moment ◽

First Principles ◽

Local Magnetic Moment ◽

Bilayer Graphene ◽

Intercalation Compounds ◽

First Principles Study ◽

Magnetic Elements

The migration and magnetic properties of the bilayer graphene with intercalation compounds (BGICs) with magnetic elements are theoretically investigated based on first principles study.

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