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Configurational and Magnetic Interactions in Multicomponent Systems
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
2010 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis is a theoretical study of configurational and magnetic interactions in multicomponent solids. These interactions are the projections onto the configurational and magnetic degrees of freedom of the underlying electronic quantum mechanical system, and can be used to model, explain and predict the properties of materials. For example, the interactions govern temperature induced configurational and magnetic order-disorder transitions in Heusler alloys and ternary nitrides.

In particular three perspectives are studied. The first is how the interactions can be derived from first-principles calculations at relevant physical conditions. The second is their consequences, like the critical temperatures for disordering, obtained with e.g. Monte Carlo simulations. The third is their origin in terms of the underlying electronic structure of the materials.

Intrinsic defects in the half-Heusler system NiMnSb are studied and it is found that low-energy defects do not destroy the important half-metallic property at low concentrations. Deliberate doping of NiMnSb with 3d-metals is considered and it is found that replacing some Ni with extra Mn or Cr creates new strong magnetic interactions which could be beneficial for applications at elevated temperature. A self-consistent scheme to include the effects of thermal expansion and one-electron excitations in the calculation of the magnetic critical temperature is introduced and applied to a study of Ni1−xCuxMnSb.

A supercell implementation of the disordered local moments approach is suggested and benchmarked for the treatment of paramagnetic CrN as a disordered magnetic phase. It is found that the orthorhombic-to-cubic phase transition in this nitride can be understood as a first-order magnetic order-disorder transition. The ferromagnetism in Ti1−xCrxN solid solutions, an unusual property in nitrides, is explained in terms of a charge transfer induced change in the Cr-Cr magnetic interactions.

Cubic Ti1−xAlxN solid solutions displays a complex and concentration dependent phase separation tendency. A unified cluster expansion method is presented that can be used to simulate the configurational thermodynamics of this system. It is shown that short range clustering do influence the free energy of mixing but only slightly change the isostructural phase diagram as compared to mean-field estimates.

Ort, förlag, år, upplaga, sidor
Linköping: Linköpings Universitet , 2010. , s. 98
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1334
Nyckelord [en]
Magnetic interactions, Configurational thermodynamics, Curie temperature, theoretical physics, magnetism, TiAlN, TiN, AlN, CrN, TiCrN, nitrides, NiMnSb, NiCuMnSb, Heusler alloys, spintronics, half-metallic, spinodal decomposition, first-principles, ab-initio
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
URN: urn:nbn:se:liu:diva-60446ISBN: 978-91-7393-330-8 (tryckt)OAI: oai:DiVA.org:liu-60446DiVA, id: diva2:356676
Disputation
2010-09-09, Planck, Fysikhuset, Campus Valla, Linköping University, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2010-11-17 Skapad: 2010-10-13 Senast uppdaterad: 2020-02-19Bibliografiskt granskad
Delarbeten
1. Role of stoichiometric and nonstoichiometric defects on the magnetic properties of the half-metallic ferromagnet NiMnSb
Öppna denna publikation i ny flik eller fönster >>Role of stoichiometric and nonstoichiometric defects on the magnetic properties of the half-metallic ferromagnet NiMnSb
2006 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 6, s. 064418-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The first material to be predicted from first-principles calculations as half-metallic was NiMnSb, and the research on this material has been intense due to its possible applications in spintronics devices. The failure of many experiments to measure spin polarization to more than a fraction of the predicted 100% has partly been blamed on structural defects. In this work a complete first-principles treatise of point defects, including nonstoichiometric antisites, interstitial and vacancy defects, as well as stoichiometric atomic swap defects in NiMnSb, is presented. We find that the formation energies of the defects span a large scale from 0.2 to 14.4 eV. The defects with low formation energies preserve the half-metallic character of the material. We also find that some of the defects increase the magnetic moment and thus can explain the experimentally observed increase of magnetic moments in some samples of NiMnSb. Most interesting in this respect are Mn interstitials which increase the magnetic moment, have a low formation energy, and keep the half-metallic character of the material.

Nyckelord
nickel alloys, manganese alloys, antimony alloys, ferromagnetic materials, ab initio calculations, interstitials, antisite defects, vacancies (crystal), defect states, magnetic moments
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-35025 (URN)10.1103/PhysRevB.73.064418 (DOI)24646 (Lokalt ID)24646 (Arkivnummer)24646 (OAI)
Anmärkning
Original Publication: Björn Alling, Sam Shallcross and Igor Abrikosov, Role of stoichiometric and nonstoichiometric defects on the magnetic properties of the half-metallic ferromagnet NiMnSb, 2006, Physical Review B. Condensed Matter and Materials Physics, (73), 6, 064418. http://dx.doi.org/10.1103/PhysRevB.73.064418 Copyright: American Physical Society http://www.aps.org/ Tillgänglig från: 2009-10-10 Skapad: 2009-10-10 Senast uppdaterad: 2017-12-13
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4. Competition between Magnetic Structures in the Fe-Rich FCC FeNi Alloys
Öppna denna publikation i ny flik eller fönster >>Competition between Magnetic Structures in the Fe-Rich FCC FeNi Alloys
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2007 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 1, s. 014434-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We report on the results of a systematic ab initio study of the magnetic structure of Fe rich fcc FeNi binary alloys for Ni concentrations up to 50 at. %. Calculations are carried out within density-functional theory using two complementary techniques, one based on the exact muffin-tin orbital theory within the coherent potential approximation and another one based on the projector augmented-wave method. We observe that the evolution of the magnetic structure of the alloy with increasing Ni concentration is determined by a competition between a large number of magnetic states, collinear as well as noncollinear, all close in energy. We emphasize a series of transitions between these magnetic structures, in particular we have investigated a competition between disordered local moment configurations, spin spiral states, the double layer antiferromagnetic state, and the ferromagnetic phase, as well as the ferrimagnetic phase with a single spin flipped with respect to all others. We show that the latter should be particularly important for the understanding of the magnetic structure of the Invar alloys.

Ort, förlag, år, upplaga, sidor
American Physical Society, 2007
Nyckelord
Iron alloys, nickel alloys, ferromagnetic materials, magnetic structure, ab initio calculations, density functional theory, linear muffin-tin orbital method, local moments
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-14277 (URN)10.1103/PhysRevB.76.014434 (DOI)
Anmärkning
Original Publication: Igor A. Abrikosov, Andreas E. Kissavos, Francois Liot, Björn Alling, Sergey Simak, O. Peil and A. V. Ruban, Competition between Magnetic Structures in the Fe-Rich FCC FeNi Alloys, 2007, Physical Review B Condensed Matter, (76), 1, 014434. http://dx.doi.org/10.1103/PhysRevB.76.014434 Copyright: American Physical Society http://www.aps.org/Tillgänglig från: 2007-02-01 Skapad: 2007-02-01 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
5. Questionable collapse of the bulk modulus in CrN
Öppna denna publikation i ny flik eller fönster >>Questionable collapse of the bulk modulus in CrN
2010 (Engelska)Ingår i: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 9, nr 4, s. 283-284Artikel i tidskrift, Letter (Övrigt vetenskapligt) Published
Abstract [en]

In this comment we show that the main conclusion in a previous article, claiminga drastic increase in compressibility of CrN at the cubic to orthorhombic phasetransition, is unsupported by first-principles calculations. We show that if thecubic CrN phase is considered as a disordered magnetic material, as supported bydifferent experimental data, rather then non-magnetic, the bulk modulus is almostunaffected by the transition.

Ort, förlag, år, upplaga, sidor
London, UK: Nature Publishing Group, 2010
Nyckelord
CrN, phase-transition, magnetism, bulk modulus, first-principles
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-60438 (URN)10.1038/nmat2722 (DOI)000275901000002 ()
Tillgänglig från: 2010-10-13 Skapad: 2010-10-13 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
6. Effect of magnetic disorder and strong electron correlations on the thermodynamics of CrN
Öppna denna publikation i ny flik eller fönster >>Effect of magnetic disorder and strong electron correlations on the thermodynamics of CrN
2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, s. 184430-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Two different methods for the modeling of a magnetically disordered CrN stateusing a supercell approach are investigated. They are found to give equivalentresults of the total energy, being also similar to results obtained with an effectivemedium approach. Furthermore, CrN is shown to be better described using aLDA+U framework for the treatment of electron-electron correlations as comparedto GGA or LDA calculations. Modeling the cubic paramagnetic phase with ourmodels for magnetic disorder and considering the strong electron correlations, thetemperature and pressure induced phase transitions in CrN can be explained.

Ort, förlag, år, upplaga, sidor
American institute of physics, 2010
Nyckelord
CrN, magnetic disorder, nitrides, LDA+U, SQS, phase transition, chromium compounds
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-60439 (URN)10.1103/PhysRevB.82.184430 (DOI)000291462500005 ()
Tillgänglig från: 2010-10-13 Skapad: 2010-10-13 Senast uppdaterad: 2017-12-12
7. Theory of the ferromagnetism in Ti1-xCrxN solid solutions
Öppna denna publikation i ny flik eller fönster >>Theory of the ferromagnetism in Ti1-xCrxN solid solutions
2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 5, s. 054408-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

First-principles calculations are used to investigate the magnetic properties of Ti1‑xCrxN solid solutions. We show that the magnetic interactions between Cr spins that favor antiferromagnetism in CrN is changed upon alloying with TiN leading to the appearance of ferromagnetism in the system at approximately x≤0.50 in agreement with experimental reports. Furthermore we suggest that this effect originates in an electron density redistribution from Ti to Cr that decreases the polarization of Crd states with t2g symmetry while it increases the polarization of Crd states with eg symmetry, both changes working in favor of ferromagnetism.

Nyckelord
TiN, CrN, TiCrN, solid solutions, first-principles, magnetic interactions, ferromagnetism, electronic structure
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-60441 (URN)10.1103/PhysRevB.82.054408 (DOI)
Anmärkning
Original Publication: Björn Alling, Theory of the ferromagnetism in Ti1-xCrxN solid solutions, 2010, Physical Review B Condensed Matter, (82), 5, 054408. http://dx.doi.org/10.1103/PhysRevB.82.054408 Copyright: American Physical Society http://www.aps.org/Tillgänglig från: 2010-10-13 Skapad: 2010-10-13 Senast uppdaterad: 2017-12-12
8. A unified cluster expansion method applied to the configurational thermodynamics of cubic TiAlN
Öppna denna publikation i ny flik eller fönster >>A unified cluster expansion method applied to the configurational thermodynamics of cubic TiAlN
Visa övriga...
2011 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 10, s. 104203-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We use a study of the cubic Ti1−xAlxN system to illustrate a practical way of combining the major methodologies within alloy theory, the Connolly-Williams cluster expansion and the generalized perturbation method, in order to solve difficult alloy problems. The configurational, concentration dependent, Hamiltonian is separated into a fixed-lattice and a local lattice relaxation part. The effective cluster interactions of the first part is obtained primarily with a GPM-based approach while the later is obtained using cluster expansion. In our case the impact on the isostructural phase diagram of considering short range clustering beyond the mean field approximation, obtained from the mixing enthalpy and entropy of the random alloy, is rather small, especially in the composition region x ≤ 0.66, within reach of thin film growth techniques.

Ort, förlag, år, upplaga, sidor
American Physical Society, 2011
Nyckelord
TiAlN, TiN, AlN, cluster expansion, GPM, spinodal decomposition, first-principles, titanium aluminium nitride, clustering, phase separation
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-60442 (URN)10.1103/PhysRevB.83.104203 (DOI)000288782700004 ()
Anmärkning
Original Publication: Björn Alling, A. V. Ruban, A Karimi, Lars Hultman and Igor Abrikosov, A unified cluster expansion method applied to the configurational thermodynamics of cubic TiAlN, 2011, Physical Review B. Condensed Matter and Materials Physics, (83), 10, 104203. http://dx.doi.org/10.1103/PhysRevB.83.104203 Copyright: American Physical Society http://www.aps.org/ Tillgänglig från: 2010-10-13 Skapad: 2010-10-13 Senast uppdaterad: 2017-12-12
9. Pressure enhancement of the isostructural cubic decomposition in Ti1−xAlxN
Öppna denna publikation i ny flik eller fönster >>Pressure enhancement of the isostructural cubic decomposition in Ti1−xAlxN
2009 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, nr 181906Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The influence of pressure on the phase stabilities of Ti1−xAlxN solid solutions has been studied using first principles calculations. We find that the application of hydrostatic pressure enhances the tendency for isostructural decomposition, including spinodal decomposition. The effect originates in the gradual pressure stabilization of cubic AlN with respect to the wurtzite structure and an increased isostructural cubic mixing enthalpy with increased pressure. The influence is sufficiently strong in the composition-temperature interval corresponding to a shoulder of the spinodal line that it could impact the stability of the material at pressures achievable in the tool-work piece contact during cutting operations

Nyckelord
ab initio calculations, aluminium compounds, enthalpy, high-pressure effects, mixing, solid solutions, spinodal decomposition, titanium compounds
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-51569 (URN)10.1063/1.3256196 (DOI)
Anmärkning
Original Publication: Björn Alling, Magnus Odén, Lars Hultman and Igor Abrikosov, Pressure enhancement of the isostructural cubic decomposition in Ti1-xAlxN, 2009, Applied Physics Letters, (95), 181906. http://dx.doi.org/10.1063/1.3256196 Copyright: American Institute of Physics http://www.aip.org/ Tillgänglig från: 2009-11-07 Skapad: 2009-11-07 Senast uppdaterad: 2017-12-12
10. Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions
Öppna denna publikation i ny flik eller fönster >>Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions
Visa övriga...
2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 22, s. 224101-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Thin solid films of metastable rocksalt structure (c-) Sc1-xAlxN and Ti1-xAlxN were employed as model systems to investigate the relative influence of volume mismatch and electronic structure driving forces for phase separation. Reactive dual magnetron sputtering was used to deposit stoichiometric Sc0.57Al0.43N(111) and Ti0.51Al0.49N(111) thin films, at 675 °C and 600 °C, respectively, followed by stepwise annealing to a maximum temperature of 1100 °C. Phase transformations during growth and annealing were followed in situ using X-ray scattering. The results show that the as-deposited Sc0.57Al0.43N films phase separate at 1000 °C – 1100 °C into non-isostructural c-ScN and wurtzite-structure (w-) AlN, via nucleation and growth at domain boundaries. Ti0.51Al0.49N, however, exhibits spinodal decomposition into isostructural coherent c-TiN and c-AlN, in the temperature interval of 800 °C – 1000 °C. X-ray pole figures show the coherency between c-ScN and w-AlN, with AlN(0001) || ScN(001) and AlN<01ɸ10> || ScN<1ɸ10>. First principles calculations of mixing energy-lattice spacing curves explain the results on a fundamental physics level and open a route for design of novel metastable pseudobinary phases for hard coatings and electronic materials.

Nyckelord
TiAlN, ScAlN, spinodal decomposition, nitrides, TiN, ScN, AlN, XRD, TEM, first-principles, phase separation, meta stable
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-56270 (URN)10.1103/PhysRevB.81.224101 (DOI)000278300900004 ()
Anmärkning
Original Publication: Carina Höglund, Björn Alling, Jens Birch, Manfred Beckers, Per O. Å. Persson, Carsten Baehtz, Zsolt Czigány, Jens Jensen and Lars Hultman, Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions, 2010, Physical Review B. Condensed Matter and Materials Physics, (81), 22, 224101. http://dx.doi.org/10.1103/PhysRevB.81.224101 Copyright: American Physical Society http://www.aps.org/ Tillgänglig från: 2010-05-06 Skapad: 2010-05-06 Senast uppdaterad: 2017-12-12
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