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Theory of the ferromagnetism in Ti1-xCrxN solid solutions
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
2010 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, nr 5, s. 054408-Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
2010. Vol. 82, nr 5, s. 054408-
Emneord [en]
TiN, CrN, TiCrN, solid solutions, first-principles, magnetic interactions, ferromagnetism, electronic structure
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-60441DOI: 10.1103/PhysRevB.82.054408OAI: oai:DiVA.org:liu-60441DiVA, id: diva2:356624
Merknad
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/Tilgjengelig fra: 2010-10-13 Laget: 2010-10-13 Sist oppdatert: 2017-12-12
Inngår i avhandling
1. Configurational and Magnetic Interactions in Multicomponent Systems
Åpne denne publikasjonen i ny fane eller vindu >>Configurational and Magnetic Interactions in Multicomponent Systems
2010 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Linköping: Linköpings Universitet, 2010. s. 98
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1334
Emneord
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
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-60446 (URN)978-91-7393-330-8 (ISBN)
Disputas
2010-09-09, Planck, Fysikhuset, Campus Valla, Linköping University, Linköping, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2010-11-17 Laget: 2010-10-13 Sist oppdatert: 2020-02-19bibliografisk kontrollert

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