Structural, Electronic, Magnetic and Mechanical
properties of CoO and NiO: ab-initio study
A. Jemmy Cinthiaa, G. Sudha Priyangaa, M. Santhosha, R. Rajeswarapalanichamya,*, K. Iyakuttib
a
Department of physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019, India
Department of physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203. India.
*Corresponding author E-mail: rrpalanichamy@gmail.com, Tel.: +91-9486928092; Fax: 0452-2458358
b
Abstract
The structural, electronic, magnetic and mechanical
properties of NaCl phase of CoO and NiO are analyzed.
The total energies are calculated for various pressures and
it is found that both the compounds are stable in
antiferromagnetic state at normal pressure.
Keywords: electronic structure; mechanical properties;
magnetic phase transition.
Introduction
The transition metal monoxides CoO and NiO
have interesting structural and magnetic properties.
These are antiferromagnetic insulators [1], having
srrong correlation effects associated with the transition
metal 3d electrons. Employing the Hubbard U
corrections to the LDA calculations greatly improves
the band gaps and the magnetic properties of CoO and
NiO.
The antiferromagnetic (AFM) phase is found to be the
most stable state when compared to the ferromagnetic
(FM) and the non-magnetic (NM) phases (Fig.1). The
indirect band gap Eg values of CoO and NiO shown in
table 2 along with experimental result [5], indicates that
the LDA calculation underestimates the band gap
values; whereas the LDA+U calculations improves the
band gap values to a great extent. A pressure driven
antiferromagnetic to ferromagnetic transition is
observed in NiO at a pressure of 84 GPa. The calculated
elastic constants indicate that both CoO and NiO are
mechanically stable at normal pressure.
Table.2 Band gap values of CoO and NiO
Eg (eV)
(LDA)
CoO
NiO
0.61
0.753
Eg (eV)
(LDA+U)
U=8 eV
1.77
3.45
Expt
(eV)
2.6[5]
4.0[5]
Computational details
All computations are carried out using Vienna
ab initio simulation package (VASP) [2] with the local
density approximation (LDA) approximation to DFT
and with the LDA+U extension to it.
Results and discussion
The computed ground state properties are
given in Table 1 for the AFM phase of CoO and NiO
along with the available experimental results [3, 4].
Table.1. lattice constant a (Å), volume V0 (Å3), VED ρ
(electrons/ Å3), magnetic moment, bulk modulus B0 and
its derivative B0'.
a
V0
ρ
µB
B0
B0'
CoO
NiO
4.213
4.25[3]
18.69
0.802
2.411
3.84[4]
228
4.0
4.16
4.171[3]
18.0
0.888
1.326
1.9[4]
194
4.0
Fig.1. Volume vs Energy for the AFM, FM and NM
states of CoO and NiO.
Acknowledgment
We thank our college management for their
constant encouragement.
References
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[2]
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[4]
[5]
B.H. Brandow, Adv. Phys. 26 (1977) 651.
G. Kresse , J. Hafner , Phys. Rev. B 47 (1993) 558.
F. Tran, P. Blaha, Phys. Rev. B 74 (2006) 155108.
V.I.Anisimov, J.Zaanen, Phys.Rev.B 44(1991) 943.
E.Z. Kurmaev, Phys. Rev. B 77(2008)165127.