Vol.:(0123456789) 1 3
Journal of Materials Science: Materials in Electronics
https://doi.org/10.1007/s10854-018-0366-5
Structural and magnetic properties of CoMn
2
O
4
synthesized by auto
combustion method
Rajeesh Kumar Narayanan Kutty
1
· Palanisamy Rupa Kasturi
1
· Jaya Jaganath
1
· Saravanan Padmanapan
2
·
Yun Sung Lee
3
· Danielle Meyrick
4
· Ramakrishnan Kalai Selvan
1
Received: 28 August 2018 / Accepted: 12 November 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Combustion synthesized cobalt manganite (CMO) was systematically studied for its structural and magnetic properties.
X-ray difraction (XRD) pattern with high-intensity peaks at appropriate positions revealed the formation of phase pure
and highly crystalline CMO. The distorted tetragonal structure of the CMO unit cell suggested the presence of high spin
(d
4
) Jahn–Teller Mn
3+
ions. X-ray photoelectron spectra (XPS) supported a mixed spinel with Co
2+
, Co
3+
, Mn
2+
and Mn
3+
cations. Electron microscopy confrmed the formation of submicron-sized CMO particles with well-defned lattice fringes,
while low-temperature magnetic investigations revealed that the prepared CMO as a ferrimagnetic spinel due to the presence
of uncompensated electronic states. The observed unsaturated magnetization, even at large applied felds, confrmed the high
degree of spin-canting due to the existence of Yafet–Kittel spin arrangement.
1 Introduction
Spinel structured metal oxides are an interesting class of
materials, which is known for their exciting magnetic prop-
erties and phase transition phenomena like Verwey transi-
tion, antiferromagnetic frustration, spin-glass state, com-
mensurate-incommensurate phases, magneto-elastic and
magnetodielectric coupling etc. [1–6]. These interesting
properties naturally lead them to fnd application in multi-
ferroics, spintronics, drug delivery etc. According to Bragg
and Nishikawa, the AB
2
O
4
structured spinel consists of a
cubic closely-packed array of cations with more than one
oxidation state occupying the tetrahedral (A) and octahedral
(B) sites coordinated with oxygen atoms [7, 8]. The cationic
distribution of spinel is represented as (A
1−x
B
x
)[A
x
B
2−x
]O
4
,
where x denotes the degree of inversion. When x = 0, the
formed one is a normal spinel and when x = 1, an inverse
spinel is formed. When x picks up an intermediate value
between 0 and 1, a mixed spinel is obtained. The cation dis-
tribution plays a considerable role in altering the properties
of spinel oxides. Site preference of cations depends upon (i)
ion size, (ii) electronic confguration of ion and (iii) strength
and symmetry of crystal fled at the site [9]. The dominant
exchange interaction between and within the ocathedral (B)
and tetrahedral (A) sub-lattices dictate the kind of magnetic
ordering developed in the material. According to Neel’s two
sub-lattice model, A–B interactions are more stronger than
A–A or B–B interactions. Owing to the inequality in the
number of ions in the tetrahedral and octahedral sites and the
strong exchange interaction between the sub-lattices leads to
ferrimagnetic ordering [10].
Magnetic properties of the Mn-rich spinel oxides
(ZnMn
2
O
4
, CoMn
2
O
4
, FeMn
2
O
4
) are explored relatively less
when compared to that of Fe-rich spinel oxides (e.g. Fe
3
O
4
,
MnFe
2
O
4
, NiFe
2
O
4
). This may be due to the requirement
of the low-temperature magnetic measurement system and
complex magnetic behaviour of Mn-rich spinels. Mn
3
O
4
is
a ferrimagnetic spinel evidencing triangular spin arrange-
ment as suggested by Yafet and Kittel rather than obeying
Neel’s antiparallel spin [11]. When tetrahedral sites are sub-
stituted with non-magnetic ions like Mg or Zn, magnetic
dilution efect can be observed resulting in weak exchange
* Ramakrishnan Kalai Selvan
selvankram@buc.edu.in
1
Energy Storage and Conversion Devices Laboratory,
Department of Physics, Bharathiar University, Coimbatore,
Tamil Nadu 641 046, India
2
Defence Metallurgical Research Laboratory,
Hyderabad 500 058, India
3
Faculty of Applied Chemical Engineering, Chonnam
National University, Gwangju 500-757, South Korea
4
Theranostics Australia, Richmond Quarter, 1 Silas St,
East Fremantle, WA 6158, Australia