Effect of boron content on structure and magnetic properties in
CoFe
2
O
4
spinel nanocrystals
Mustafa Akyol
a, *
,
_
Idris Adanur
b
, Ali Osman Ayas ¸
c
, Faruk Karada
g
b
, Ahmet Ekicibil
b
a
Department of Materials Engineering, Adana Science and Technology University, Adana, 01250, Turkey
b
Department of Physics, Çukurova University, 01330, Adana, Turkey
c
Department of Mechatronics Engineering, Adıyaman University, Adıyaman, 02040, Turkey
article info
Article history:
Received 8 November 2017
Received in revised form
8 February 2018
Accepted 10 February 2018
Available online 12 February 2018
Keywords:
Spinel
Magnetism
Boron
Nanocrystal
abstract
We study the effect of boron content on the structural and magnetic properties of CoFe
2
O
4
spinel
nanocrystallines synthesized by sol-gel method. The crystal structure and phase identification of samples
are studied by using X-ray diffraction experiment and Rietveld analysis. Rietveld refinement results
reveal that all samples have cubic symmetry with space group Fd3m. The cationic distributions are
obtained from Rietveld refinement that boron ions are settled into both tetrahedral and octahedral sites
in spinel lattice. The crystallite sizes of samples are found in a range of 47e67 nm that is in the limit of
single domain in such structure. All samples show ferromagnetic nature and magnetic transition was not
seen in the temperature range of 5e400 K. The magnetic domains are pinned with adding boron ions
into the CoFe
2
O
4
spinel structure at low temperatures. Thus, an increment in the propagation field (H
p
)
and temperature (T
p
) by boron content in CoFe
2
O
4
structure is observed. In addition, the saturation
magnetization (M
s
) normalized by crystal size increases with increasing boron concentration. The
temperature dependence of magnetic properties of the samples taken by experimental data are
confirmed with the Neel-Arhenius model by adding thermal dependence of magnetocrystalline
anisotropy term. The results indicate that boron-doping into the spinel structure enhances ferromagnetic
coupling and suppresses super-exchange interaction between tetrahedral (X) and octahedral (Y) sites.
© 2018 Elsevier B.V. All rights reserved.
1. Introduction
Magnetic spinel oxides chemically formulized as XY
2
O
4
where X
is a divalent cation the occupier of tetrahedral sites and Y is a
trivalent cation the occupier of octahedral sites, have great atten-
tion because of their physical interest and important applications in
high temperature ceramics, catalysis, semiconductors, electro-
chemical sensors, biomedical materials, active components of fer-
rofluids and several technological applications in nanotechnology
[1e 7]. An interesting aspect of spinel ferrite nanoparticles is their
unique magnetic properties, due to controlling of magnetic
response by the particle size and shape. Although there are various
spinel nanoparticle materials used in biomedicine and magnetic
recording, much number of researches have done to understand of
nanomagnetic ferrites. Cobalt ferrite (CoFe
2
O
4
) has commonly used
for magnetic recording applications and ferrofluids because of its
unique magnetic properties that remarkable large first order
magnetocrystalline anisotropy (K) constant compared to the other
spinel materials [8e11]. CoFe
2
O
4
materials have also used as
contrast agents in Magnetic Resonance Imaging (MRI). It is desired
for practical applications that the materials have larger magnetic
anisotropy and larger magnetic moment even their particle size is
reduced to nano-meter scale. Varying the cations on the X/Y sites
could change the magnetic interaction in antiferromagnetic X-Y
and exchange interaction Y-Y. Therefore, the research attention has
been focused mainly on the enhancement of magnetic properties of
CoFe
2
O
4
by substituting on X and Y sites with several cations, like
Cr, Zn, Ni, Mn [3, 12e17]. To reduce antiferromagnetic interactions
between d-d (Co
2þ
-Fe
3þ
) orbital electrons in spinel structure, non-
transition metal (p-orbital) can be doped into one of the site of
spinel structure. Thus, p-d exchange interaction can enhance the
effective magnetization in the whole structure.
Here, we systematically study the effect of boron content in
CoFe
2
O
4
spinel samples on structural and magnetic properties. The
structural properties and morphology of the samples were studied
* Corresponding author. Adana Science and Technology University, Department
of Materials Engineering, 01250, Sarıçam, Adana, Turkey.
E-mail address: makyol@adanabtu.edu.tr (M. Akyol).
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
https://doi.org/10.1016/j.jallcom.2018.02.121
0925-8388/© 2018 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds 744 (2018) 528e534