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Effect of magnetic disorder and strong electron correlations on the thermodynamics of CrN
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
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. Vol. 82, s. 184430-
Nyckelord [en]
CrN, magnetic disorder, nitrides, LDA+U, SQS, phase transition, chromium compounds
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:liu:diva-60439DOI: 10.1103/PhysRevB.82.184430ISI: 000291462500005OAI: oai:DiVA.org:liu-60439DiVA, id: diva2:356618
Tillgänglig från: 2010-10-13 Skapad: 2010-10-13 Senast uppdaterad: 2017-12-12
Ingår i avhandling
1. Configurational and Magnetic Interactions in Multicomponent Systems
Öppna denna publikation i ny flik eller fönster >>Configurational and Magnetic Interactions in Multicomponent Systems
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
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:nbn:se:liu:diva-60446 (URN)978-91-7393-330-8 (ISBN)
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

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