FORMATION OF MAGNETIC MOMENTS IN INTERMETALLIC COMPOUNDS AND ALLOYS

1993 ◽  
Vol 07 (01n03) ◽  
pp. 756-759 ◽  
Author(s):  
T. BEUERLE ◽  
K. HUMMLER ◽  
M. FÄHNLE
Keyword(s):  
Transition Metals ◽  
Ab Initio ◽  
Intermetallic Compounds ◽  
Magnetic Moment ◽  
Nearest Neighbor ◽  
Physical Mechanism ◽  
Magnetic Moments ◽  
Lmto Method ◽  
Minimum Number ◽  
Alloy Systems

Jaccarino and Walker proposed that in certain alloy systems a considered kind of atom attains a constant value of the magnetic moment if it is surrounded by at least a minimum number of nearest-neighbor atoms of a certain kind, and that it is nonmagnetic otherwise. It is shown by ab initio supercell calculations within the LMTO method that the system Nbi−xMox with 1% iron approximately fulfills the Jaccarino-Walker hypothesis, whereas the alloy FexRh1−x does not. The physical mechanism for the destruction of the Fe moment in bcc alloys with 4d and 5d transition metals is elucidated.

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

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1732 ◽  
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.

scholarly journals Impact of Nano-Scale Distribution of Atoms on Electronic and Magnetic Properties of Phases in Fe-Al Nanocomposites: An Ab Initio Study

Nanomaterials ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1059 ◽  
Author(s):  
Ivana Miháliková ◽  
Martin Friák ◽  
Yvonna Jirásková ◽  
David Holec ◽  
Nikola Koutná ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Nearest Neighbor ◽  
Magnetic Moments ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Α Phase ◽  
Ordered Intermetallic ◽  
Random Structures ◽  
The Impact

Quantum-mechanical calculations are applied to examine magnetic and electronic properties of phases appearing in binary Fe-Al-based nanocomposites. The calculations are carried out using the Vienna Ab-initio Simulation Package which implements density functional theory and generalized gradient approximation. The focus is on a disordered solid solution with 18.75 at. % Al in body-centered-cubic ferromagnetic iron, so-called α -phase, and an ordered intermetallic compound Fe 3 Al with the D0 3 structure. In order to reveal the impact of the actual atomic distribution in the disordered Fe-Al α -phase three different special quasi-random structures with or without the 1st and/or 2nd nearest-neighbor Al-Al pairs are used. According to our calculations, energy decreases when eliminating the 1st and 2nd nearest neighbor Al-Al pairs. On the other hand, the local magnetic moments of the Fe atoms decrease with Al concentration in the 1st coordination sphere and increase if the concentration of Al atoms increases in the 2nd one. Furthermore, when simulating Fe-Al/Fe 3 Al nanocomposites (superlattices), changes of local magnetic moments of the Fe atoms up to 0.5 μ B are predicted. These changes very sensitively depend on both the distribution of atoms and the crystallographic orientation of the interfaces.

Ab Initio Investigations of Structural and Magnetic Properties of Cr-Doped Ni-Co-Mn-Sn Heusler Alloys

2016 ◽  
Vol 845 ◽  
pp. 134-137
Author(s):  
Elizaveta E. Smolyakova ◽  
M.A. Zagrebin ◽  
V.V. Sokolovskiy ◽  
Vasiliy D. Buchelnikov
Keyword(s):  
Ab Initio ◽  
Nearest Neighbor ◽  
Magnetic Moments ◽  
Heusler Alloys ◽  
Lattice Parameter ◽  
Neighbor Interaction ◽  
Magnetic Exchange ◽  
Cr Content ◽  
Crystal Lattice Parameters ◽  
Exchange Parameters

Ab initio calculations were performed to investigate composition dependences of crystal lattice parameters, magnetic moments,bulk modulus, magnetic exchange parameters inNi2-yCoyMn1.5-xCrxSn0.5 (y =0.2, 0.4; 0.0 ≤ x ≤ 0.4) Heusler alloys. It was shown that increasing of Cr content (x) firstly leads an increasing of lattice parameter, but then a decreasing. The strongest ferromagnetic (FM) interaction for Ni1.6Co0.4Mn1.4Cr0.1Sn0.5 is nearest-neighbor interaction between Co and Mn1 (on own sites). The strongest antiferromagnetic (AFM) interaction is observed between nearest-neighbor Mn1-Cr atoms in the first coordination sphere and it is equal to-15 meV. Total magnetic moment of Ni2-yCoyMn1.5-xCrxSn0.5 (y =0.2, 0.4; 0.0 ≤ x ≤ 0.4) takes value in region from 6.1 μB to 6.6 μB.

LOCAL ORDER OF LIQUID AND UNDERCOOLED TRANSITION METAL BASED SYSTEMS: AB INITIO MOLECULAR DYNAMICS STUDY

2006 ◽  
Vol 20 (12) ◽  
pp. 655-674 ◽  
Author(s):  
NOEL JAKSE ◽  
ALAIN PASTUREL
Keyword(s):  
Molecular Dynamics ◽  
Transition Metals ◽  
Ab Initio ◽  
Liquid State ◽  
Magnetic Moments ◽  
Three Dimensional ◽  
Ab Initio Molecular Dynamics ◽  
Local Order ◽  
Pure Liquid ◽  
Common Neighbor

An overview of a recent series of ab initio molecular dynamics (MD) simulations for pure liquid transition metals as well as for transition metals (TM) based liquid alloys is presented. The aim is to investigate the local structure of these systems and their evolution upon undercooling, and our results are analyzed through a three-dimensional picture of the short-ranger order (SRO) by means of the common-neighbor analysis. Recent diffraction experiments indicate that the structure of both pure metals and alloys in undercooled states is dominated by an icosahedral SRO. We find that the five-fold symmetry is already present in the liquid state of all the studied systems. However our findings show that the five-fold symmetry in the liquid state as well as its evolution upon undercooling depends on the system under consideration. For Ni , Zr , and Ta , local configurations are more complex than that given by the simple icosahedron. For Al 80 Ni 20 and Al 80 Mn 20 alloys, local configurations are the result of a strong competition between chemical and topological effects; the key role played by the occurrence of localized magnetic moments of Mn atoms to interpret their short-range arrangements is emphasized, and the time evolution of the configurations is examined in terms of the mean square displacements.

First Principle Calculations of the Magnetic Structures of 3d Transition Metals Doped GaN

2007 ◽  
Vol 124-126 ◽  
pp. 847-850 ◽  
Author(s):  
Seung Cheol Lee ◽  
Kwang Real Lee ◽  
Kyu Hwan Lee
Keyword(s):  
Transition Metals ◽  
Magnetic Moment ◽  
Magnetic Phase ◽  
Magnetic Moments ◽  
Transition Element ◽  
First Principle ◽  
Magnetic Structures ◽  
First Principle Calculations ◽  
Electronic And Magnetic Structures ◽  
Mn Doped

First principle calculations were performed on the electronic and magnetic structures of the transition metals doped GaN. Seven elements in 3d transition metals from V to Cu were used as a dopant. Magnetic phase was stable compared to non-magnetic phase for all transition metals doped GaN. Total magnetic moments followed Hund’s rule to maximize the magnetic moment. Transition element projected magnetic moments showed that most of magnetic moments were concentrated on transition metals in the cases of V, Cr, and Mn doped GaN, which could not be used for DMS. Since Fe and Ni doped GaNs are intrinsic insulators, Fe and Ni doped GaNs could not be used for DMS materials unless additional dopants are introduced. The most probable candidates for DMS applications were predicted to be Co or Cu doped GaNs, respectively.

AB INITIO ELECTRONIC STRUCTURE CALCULATIONS OF HALF-METALLIC FERROMAGNETISM IN CALCIUM CHALCOGENIDES DOPED WITH B, C AND N

2011 ◽  
Vol 25 (18) ◽  
pp. 1537-1548 ◽  
Author(s):  
M. YOGESWARI ◽  
G. KALAPANA
Keyword(s):  
Ab Initio ◽  
Magnetic Moment ◽  
Local Density ◽  
Magnetic Moments ◽  
Electronic Band ◽  
Half Metallic ◽  
N Doping ◽  
C And N ◽  
Metallic Ferromagnetism ◽  
Half Metallic Ferromagnetism

Self-consistent ab initio calculations were carried out to study the structural, electronic and magnetic properties of nine ternary compounds Ca 4 XA 3 ( X = B , C and N ; A = S , Se and Te ). The calculations were performed by using tight-binding linear muffin tin orbital (TB-LMTO) method within the local density approximation (LDA). The calculations reveal that half-metallic ferromagnetism can be obtained for C - and N -doping with the integer magnetic moment of 2.00 μ B and 1.00 μ B per cell. However, B substitution does not induce magnetism in CaS and CaSe systems, but it produces ferromagnetism in CaTe system with magnetic moment of 2.67 μ B per cell. Moreover C - and N -doping enhance the stable ferromagnetic state in calcium chalcogenide systems. Spin-dependent electronic band structure, total and partial densities of state calculations demonstrate that localized magnetic moments substantially come from impurity atoms. Half-metallic ferromagnetism predominately originates from spin-polarization of electrons in 2p orbital states of C and N atoms. In addition, equilibrium lattice constant, bulk modulus, atomic local magnetic moments, half-metallic gap and robustness of half-metallicity have been calculated.

Ab-Initio Modelling of Point Defect-Impurity Interaction in Tungsten and other BCC Transition Metals

2008 ◽  
Vol 59 ◽  
pp. 253-256 ◽  
Author(s):  
Duc Nguyen-Manh
Keyword(s):  
Transition Metals ◽  
Ab Initio ◽  
Nearest Neighbor ◽  
Interstitial Site ◽  
Binding Energies ◽  
Stable Configuration ◽  
Tetrahedral Configuration ◽  
Octahedral Interstitial Site ◽  
Impurity Interaction ◽  
C And N

Ab-initio calculations have been performed to investigate systematically defect-impurity interaction in Tungsten and other bcc transition metals. It is found that the most stable configuration of C and N atoms is the octahedral interstitial site whereas O and H atoms are located in the tetrahedral configuration. For the particular case of bcc-W, the binding energies formed by the carbon and nitrogen atoms located at octahedral sites, and mono-vacancy on a nearest neighbor site are very large, 1.39 eV and 1.91 eV, respectively. Implication of these results of diffusion of point defects in tungsten is discussed and compared with the case of bcc-Fe.

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

Nanomaterials ◽  
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.

scholarly journals Environmental screening and ligand-field effects to magnetism in CrI3 monolayer

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
D. Soriano ◽  
A. N. Rudenko ◽  
M. I. Katsnelson ◽  
M. Rösner
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Nearest Neighbor ◽  
Hexagonal Boron Nitride ◽  
Magnetic Moments ◽  
Random Phase ◽  
Exchange Interactions ◽  
Ligand Field ◽  
Hubbard Models ◽  
Microscopic Origin

AbstractWe study the microscopic origin of magnetism in suspended and dielectrically embedded CrI3 monolayer by down-folding minimal generalized Hubbard models from ab initio calculations using the constrained random phase approximation. These models are capable of describing the formation of localized magnetic moments in CrI3 and of reproducing electronic properties of direct ab initio calculations. Utilizing the magnet force theorem, we find a multi-orbital super-exchange mechanism as the origin of magnetism in CrI3 resulting from an interplay between ferro- and anti-ferromagnetic Cr-Cr d coupling channels, which is decisively affected by the ligand p orbitals. We show how environmental screening, such as resulting from encapsulation with hexagonal boron nitride, affects the Coulomb interaction in the film and how this controls its magnetic properties. Driven by a non-monotonic interplay between nearest and next-nearest neighbor exchange interactions we find the magnon dispersion and the Curie temperature to be non-trivially affected by the environmental screening.

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