Magnetism of transition metal nanowires
Author
Ataca, Can
Advisor
Çıracı, Salim
Date
2008Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
In this thesis we investigated structural, electronic and magnetic properties
of 3d (light) transition metal (TM) atomic chains and Cr nanowires using firstprinciples
pseudopotential plane wave calculations. Infinite periodic linear, dimerized
linear and planar zigzag chain structures, as well as their short segments
consisting of finite number of atoms and chromium nanowires have been considered.
For most of the infinite periodic chains, neither linear nor dimerized linear
structures are favored; to lower their energy the chains undergo a structural transformation
to form planar zigzag and dimerized zigzag geometries. Dimerization in
both infinite and finite chains are much stronger than the usual Peierls distortion
and appear to depend on the number of 3d-electrons. As a result of dimerization,
a significant energy lowering occurs which, in turn, influences the stability and
physical properties. Metallic linear chain of vanadium becomes half-metallic upon
dimerization. Infinite linear chain of scandium also becomes half-metallic upon
transformation to the zigzag structure. The end effects influence the geometry,
energetics and the magnetic ground state of the finite chains. Structure optimization
performed using noncollinear approximation indicates significant differences
from the collinear approximation. Variation of the cohesive energy of infinite and
finite-size chains with respect to the number of 3d-electrons are found to mimic
the bulk behavior pointed out by Friedel.
Furthermore, we considered Cr nanowires, which have cross section comprising
a few (4,5 - 9,12) atoms. Chromium nanowires are found to be in a local
minimum in the Born-Oppenheimer surface and are ferrimagnetic metals. The
type of coupling, as for ferromagnetic or antiferromagnetic, between neighboring
Cr atoms depends on their interatomic distances. The spin-orbit coupling of finite
chains are found to be negligibly small for finite molecules and Cr nanowires.
Keywords
ab initiotransition metal molecules
nanowires
monatomic chains
transition metal
density functional theory
first principles