novelty characterization and enhancement of magnetic...
TRANSCRIPT
Novelty characterization and enhancement of magnetic propertiesof Co and Cu nanoferrites
Ebtesam E. Ateia1 • Asmaa A. El-Bassuony1 • Galila Abdelatif1 • Fatma S. Soliman1
Received: 10 June 2016 / Accepted: 8 August 2016 / Published online: 11 August 2016
� Springer Science+Business Media New York 2016
Abstract Cobalt and copper nano ferrites synthesized by
citrate technique were characterized by X-ray diffraction
technique, field emission scanning electron microscopy,
transmission electron micrographs, energy dispersive X-ray
spectroscopy and atomic force microscope. The average
crystallite sizes of Cu and Co were 24.7 and 37.7 nm
respectively. The magnetic properties were studied by
carrying out the hysteresis of MFe2O4 (M-Cu2?, Co2?) at
room temperature and at 77 K. The data showed that
CuFe2O4 has the lower saturation magnetization. While
CoFe2O4 has the larger coercive field due to the high
anisotropy of Co2? ions. The variation in saturation mag-
netization and coercivity for the investigated samples were
explained on the bases of exchange interactions. The
magnetic properties of the investigated samples changed at
low temperature (77 K) which were observed in shape of
the magnetic hysteresis M(H) loops as well as the coer-
civity and the squareness values. Co samples will be
hopeful for technological applications at or below room
temperature.
1 Introduction
Synthesis and application of magnetic nano particles with
sizes of a few nanometers is a subject of intense research
because of their interesting properties that make them
attractive, both from the scientific value of understanding
their properties, and the technological significance of
upgrading the performance of the existing materials [1, 2].
Nanoferrites attracted considerable interest for a number
of researchers, due to their promising technological
importance in a wide range of applications, including photo
catalysts [3, 4], magneto optical devices [5], high density
magnetic recording [6] and so on.
In the recent years, some researchers have investigated
the effect of rare earth ions [7], and different surfactant [8],
on the properties of nanoferrites. Generally, the physical
properties of ferrites are sensitive to the valence state and
distribution of cation over the tetrahedral (A-) and octa-
hedral (B-) sites of the spinel lattice. Therefore, the infor-
mation of cation distribution is essential to understand the
different physical properties of spinel ferrites [9].
Despite a large portion spinel ferrites are cubic, copper
ferrite (CuFe2O4) can have tetragonal unit-cell symmetry if
the sample is slowly cooled from high temperatures [10]. It
can be designated as a cubic close-packed arrangement of
oxygen ions with Cu2? and Fe3? ions at two different
crystallographic sites [11]. Copper is an inverse ferro-
magnetic spinel in which a small amount of Cu2? ions
migrate from octahedral B to tetrahedral A sites. On the
other hand the spinel cobalt ferrite has a cubic symmetry
and it has six crystallographic easy axes (directions) along
the cube edges of the crystal represented as \100[ and
four crystallographic hard axes (directions) across the body
diagonals denoted as \111[ [12–14]. CoFe2O4 shows
some excellent physical properties such as high coercivity,
chemical stabilities, moderate saturation magnetization,
low conductivity and good mechanical and large magnetic
anisotropy [15]. It is a hard magnetic material with a
magnetic ordering temperature around 520 �C [16].
The importance of spinel nano ferrite in many applica-
tions encourages us to through light on the properties of
& Galila Abdelatif
1 Physics Department, Faculty of Science, Cairo University,
Giza, Egypt
123
J Mater Sci: Mater Electron (2017) 28:241–249
DOI 10.1007/s10854-016-5517-y
copper and cobalt nanoferrites. The first one is a diamag-
netic (Cu) and the second is a ferromagnetic (Co) elements.
The structural and magnetic properties of them are studied
in order to get a more applicable one. On the other hand,
high surface area and small size of various nano particles
have attracted considerable attention because of novel
properties of nanostructures. Hence synthesis of nano sized
copper and cobalt ferrite structures will be important for
study.
2 Experimental work
The initial ingredients were cobalt nitrate, copper nitrate
and iron(III) nitrate. The citric acid (C(OH)(COOH)(CH2-
COOH)2�H2O) was used to enhance the homogeneous
mixing. All the powders were calcined at 600 �C for 4 h
with heating rate of 4 �C/min. The structure and crystallite
sizes were tested by X-rays diffractometer (XRD) using
Diano corporation of target Cu-Ka (k = 1.5424 A). The
nano particles average sizes were estimated using Scher-
rer’s relationship [17]. The morphology of the samples was
studied by field emission scanning electron microscopy
(FESEM) attached with EDX unit (energy dispersive X-ray
analyses) and transmission electron microscope (TEM).
Complimentary information about the surface microstruc-
ture of the investigated samples was obtained from the
three dimensional atomic force microscopy (AFM) images
using Wet-SPM-9600 (Scanning Probe microscope) Shi-
madzu made in Japan, Non Contact mode. The specific
surface area (SBET) was determined by Brunauer–Emmet–
Teller (BET) method [18] based on adsorption/desorption
isotherms of nitrogen at 77 K obtained with NOVA 2200,
USA, Automated gas sorption system. The magnetization
M (emu/g) was measured at room temperature and at 77 K
using a vibrating sample magnetometer (VSM) Model
Lake Shore 7410.
3 Results and discussion
The structure of the investigated nanoferrite samples
CoFe2O4 and CuFe2O4 are analyzed using X-ray diffrac-
tion (Fig. 1a, b). The XRD patterns are compared and
indexed using ICDD card no. (00-006-0545) and (04-005-
7078) for Cu and Co respectively. The broadness of the
peaks is characteristic of particles with nanometer dimen-
sions. The XRD patterns also confirm the formation of
tetragonal and cubic spinel structure for copper and cobalt
samples respectively. No extra lines corresponding to any
other phase or non-reacted ingredients are detected.
Average crystallite sizes of the samples are calculated and
the obtained data will be discussed latter. The theoretical
lattice parameter can be calculated [19] by using the pre-
dictable cation distribution of the system as shown in
Table 1. The small deviation between the theoretical lattice
parameter and experimental one gives the indication that
the cation distribution is deeply modified due to the
preparation conditions. Also it is attributed to the redistri-
bution of cations among the available A- and B-sites of the
spinel lattice.
Generally, the A- and B-site lengths are adjusted by
variation in oxygen parameter (u) until A-and B-site vol-
umes ‘‘best fit’’ the cations. The experimental oxygen
positional parameters [20] are reported in Table 1. In all
spinel ferrite the (u) parameter has a value near (0.375 A)
[21]. For the investigated samples (u) is agree well with the
theoretical and expected results.
According to Roderick et al. [22] the tolerance factor, T,
for the spinel structured materials is calculated from the
following equation:
T ¼ 1ffiffiffi
3p rA þ Ro
rB þ Ro
� �
þ 1ffiffiffi
2p Ro
rB þ Ro
� �
ð1Þ
where Ro is the radius of the oxygen ion (0.138 nm) [23],
rA and rB are the ionic radii of tetrahedral (A) and octa-
hedral (B) sites respectively.
For an ideal spinel structure tolerance factor (T) values
are close to unity. It is found that for all the synthesized
ferrites, value of T is close to unity suggesting defect free
formation of spinel structure. Figure 2a, b illustrates the
FESEM micrographs of CoFe2O4 and CuFe2O4. Figure 2a
shows heavily concentrated particles of nano scale nature
for CoFe2O4. This is due to its permanent magnetic
moment, hence each particle is permanently magnetized
and gets agglomerated. In the other words cobalt
0
20
40
60
80
100
10 20 30 40 50 60 70 80
Inte
nsity
(C
ount
s/se
c ) card
co
(220)
(311)
(400)(422)
(511)(400)
(b)
0
20
40
60
80
100
10 20 30 40 50 60 70 80
Inte
nsity
(C
ount
s/se
c)
2θ(o)
cu
card(202)(310)
(311)
(400) (404)(a)
2θ(o)
Fig. 1 The X-ray diffraction patterns for a CuFe2O4 and b CoFe2O4
nanoferrites
242 J Mater Sci: Mater Electron (2017) 28:241–249
123
nanoferrite sample possess cations which are highly mag-
netic in nature, Co2? (3 BM), Fe3? (5 BM) such clustering
of nano particles is expected.
It is clear from the figure that the cobalt nano particles
have clusters of irregularly shaped. While for CuFe2O4
samples the agglomerated particles are lower than that for
Co samples as shown in Fig. 2b. This can be attributed to
the nature of Cu samples. In the present case, from FESEM
images it is not possible to estimate particle size accurately
but in broad sense. The calculated particles sizes from
FESEM are shown in Table 2.
Figure 3a–d illustrates the transmission electron micro-
graphs (TEM) for CuFe2O4 and Co2Fe2O4 samples toge-
ther with the selected area electron diffraction patterns
(SAED).
The grain shape of CoFe2O4 sample is roughly spherical
and highly agglomerated. In contrast the grain of CuFe2O4
sample has little agglomeration and consists of platelets
with fine granular nanostructure. Figure 3b, d shows the
size distribution of the investigated samples and the mean
particle sizes are given in Table 2. The average particle
sizes are 39.15 and 30.04 nm for Co and Cu respectively.
The selected area electron diffraction (SAED) pattern
consists of concentric rings with spots over the rings. This
feature indicates that the samples are good nano crystalline
in nature [24]. The rings with a dotted pattern in SAED
confirm the wide size distribution of ferrite nano particles.
Figure 4a, b shows the surface topography and his-
tograms of CoFe2O4 and CuFe2O4 respectively. The par-
ticle sizes for the investigated samples are calculated and
tabulated in the Table 2.
From the figure it is noticed that the mean particle sizes
are in agreement with those obtained from XRD FESEM
and TEM analyses. As shown from Table 2 the particle
size estimated from FESEM, TEM and AFM analyses are
greater than the crystallite size estimated from X-ray
Table 1 Values of the theoretical (ath) and experimental (aexp) lattice parameter (a), experimental oxygen parameter (u), theoretical density and
tolerance factor for CoFe2O4 and CuFe204
Cation distribution atheo. (A) aexp (A) uexp. Dx (g/cm3) Tolerance factor
(Fe2?) Co2þ0:85Co3þ0:15Fe
3þ� �
O4 8.3853 8.382 0.377 5.295 0.990
Cu2þ0:1Fe3þ0:9
� �
Cu2þ0:9Fe3þ1:1
� �
O4 8.210 a = 8.221
c = 8.709
0.374 5.714 0.998
Fig. 2 FESEM images of: a CoFe2O4 and b CuFe2O4 nanoferrites
Table 2 The calculated crystallite size, particle size, surface area, pore size and pore volume
Samples Crystallite size
(Xray) (nm)
Particles size estimated
from (AFM) (nm)
Particles size estimated
from (FESEM) (nm)
Particles size estimated
from (TEM)(nm)
Pore size
(nm)
Pore volume
(CC/g)
CoFe2O4 37.73 38.88 38.91 39.15 2.22 0.099
CuFe2O4 24.78 29.16 30.25 30.04 2.58 0.076
J Mater Sci: Mater Electron (2017) 28:241–249 243
123
diffraction pattern. This is because of the fact that X-ray
diffraction gives the information of crystalline region only
and the contribution from the amorphous grain surface
does not considered.
Physical properties such as pore volume and pore size
distributions of particles and agglomerates are closely cor-
related to the particle size. The BET parameters are calcu-
lated and tabulated in Table 2. The obtained data shows that
the high particle size of Co nanoferrite agrees well with
highly agglomerated particles as shown in Figs. 2, 3. Also
the pore size and pore volume confirm that CoFe2O4 is non-
porous material [25]. The pore size distribution (PSD)
graphs are inserted in Fig. 4a from which one can observed
that all pore size ranges collapse within the nano sized
region. On the other hand, the obtained data for copper is
characterized by small particle size and large pore size.
Figure 5a, b shows the energy dispersive X-ray spec-
troscopy (EDEX) analysis for the investigated samples.
The energy of the K, L and M series X-rays increase with
increasing atomic number (Z). Light and Intermediate
elements will emit X-rays of the L series or K and L series.
In the spinel ferrite system under investigation, CoFe2O4,
CuFe2O4 consists of light elements like oxygen
(O) (Z = 8), intermediate elements such as Cobalt (Co)
(Z = 27), copper (Cu) (Z = 29) and Iron (Fe) (Z = 26).
The obtained weight percentage of Co, Cu, Fe and O are in
comparable values with the stoichiometric ratios of
CuFe2O4 and CoFe2O4.
The atomic percentage (at.%) and weight percentage
(wt%) of constituent elements (Co, Cu, Fe and O) are
calculated theoretically from the given formula CoFe2O4
and CuFe2O4. The obtained data from EDAX elemental
analysis is shown as inset of the figure. It can be seen that
the stoichiometry is very close to the estimated values.
Finally, by analyzing XRD, HRSEM,BET, AFM and
EDAX one can have almost complete picture of the par-
ticles size distribution and their morphology.
Figure 6a–c shows the hysteresis loops of the investi-
gated samples using a vibrating sample magnetometer
(VSM) at room temperature and 77 K. From the figure it is
clear that the magnetization increases with the applied
magnetic field until reaching saturation behavior.
Fig. 3 a, c the TEM images
and the SAED of a CuFe2O4
and c CoFe2O4 nanoferrites. b,d the size distribution of the
investigated samples
244 J Mater Sci: Mater Electron (2017) 28:241–249
123
The hysteresis curves and their properties such as the
retentivity (Mr), coercivity (Hc), squareness ratio and
hysteresis loss are summarized in Table 3.
Generally, the size and shape of the hysteresis curve for
ferromagnetic materials are of considerable practical
importance. Large M–H loop area is observed for CoFe2O4
which has the largest positive anisotropy value due to the
strong spin orbit coupling at Co2? lattice sites. This agrees
well with the calculated value of Hc as shown in the
Table 3.
The magnetization of the investigated samples can be
explained as Cu1? ions are non-magnetic due to completely
filled 3d shells which may be migrated to the tetrahedral
(A) site reducing the strength of the A-B exchange inter-
action. While Co2? ions have seven d electrons three of
them are unpaired, for this reason the magnetization values
are awarded as follows: MS (Co)[MS (Cu). As shown
from the table the saturation magnetization of cobalt ferrite
is approximately equal to 66.8 emu/g which is 67 % larger
than the value of 22.06 emu/g for copper ferrite. Also the
coercivity value at 77 K is found to be twice as large as Hc
at room temperature. This increase may be explained on
the basis of domain structure, critical diameter, strains and
shape anisotropy of crystal [26].
The maximum energy density of a permanent magnet
(MH)max is determined by the point on the second-quadrant
branch of the M–H loop (Fig. 6a). This gives the largest
area for an enclosed rectangle. In the case of Co sample the
maximum energy product is 1.592 kJ/m3. This is repre-
sentative the energy required to demagnetize a permanent
magnet. The location of (MH)max is the point at which the
material characteristics of a magnet are most efficiently
used. As shown from Table 3 the magnetization value at a
given temperature (77 K) is significantly higher for cobalt
ferrite with lower surface roughness of 1.2 A compared to
copper ferrite with higher surface roughness of 1.5 A. The
existence or absence of the different types of inter grain
group exchanges is determined by the value of Mr/Ms that
varies from 0 to 1 [27]. It has been reported that Mr/
Ms\ 0.5 is for the particle interact by magneto static
0.00E+00
4.00E-04
8.00E-04
1.20E-03
1.60E-03
0204060
dV(W
) cc/
Å/g
m
Pore size (Å)
CuCo
(a)
(b)
Fig. 4 Represents 3D AFM micrographs for a CoFe2O4 and b CuFe2O4 nanoferrites. The inset of a represents the variation of pore size with
pore volume
J Mater Sci: Mater Electron (2017) 28:241–249 245
123
interaction. While Mr/Ms = 0.5 is for randomly oriented
non interacting particles that undergo coherent rotations
[28–30]. Finally, the value of 1[Mr/Ms[ 0.5 confirms
the existence of exchange coupling particles. Therefore Mr/
Ms ratio for copper samples is attributed to have randomly
oriented non interacting particles.
On the other hand, cobalt particles interaction changes
from magneto static at room temperature to exchange
coupling at 77 K. In the case of Cu Fe2O4 the change of the
temperature from RT to 77 K nearly has no effect on the
Mr/Ms, while this ratio is doubled for CoFe2O4. Also the
value of anisotropy constant for cobalt (K = 55 9 104 erg/
cm3) is almost 10 times greater than anisotropy at room
temperature. This means that, this material will be a
guaranteeing hopeful for technological applications at or
below room temperature.
Figure 7a, b correlates the molar magnetic suscepti-
bility with the absolute temperature for cobalt and copper
nano ferrite samples at constant magnetic field intensity
(H = 5000 Oe). From the figure it is clear that vMdecreases steadily with increasing temperature then
decreases drastically to reach its minimum value. This is
well known behavior and was explained in the previous
work [31]. The calculated Curie temperature from dvm/dTas accurate value is shown in inset of the figure. The
obtained data obeys the well known Curie–Weiss law
where vm varies linearly with temperature in the param-
agnetic region. The values of the Curie constant and the
effective magnetic moment are calculated from the
reciprocal of magnetic susceptibility with absolute tem-
perature (not present here) and by using the following
equation [31].
C ¼ 1
slopeleff ¼ 2:83
ffiffiffiffi
Cp
ð2Þ
The Curie–Weiss constant h is calculated from the
intercept of the straight line with the temperature axis. The
experimental data is fitted linearly and the magnetic
parameters are calculated and tabulated in Table 4. The
experimental C values provide information on the number
of unpaired electrons in the investigated system which
agrees well with the magnetic data.
Fig. 5 The energy dispersive
X-ray spectroscopy (EDEX) for
a CoFe2O4 and b CuFe2O4
nanoferrites
246 J Mater Sci: Mater Electron (2017) 28:241–249
123
-30
-20
-10
0
10
20
30
-40000 -20000 0 20000 40000
Mag
netiz
atio
n (e
mu/
g)
magnetic field (Oe)
Cu
room
77K
(b)
-80-60-40-200
204060
-30000 -20000 -10000 0 10000 20000 30000
Mag
netiz
atio
n (e
mu/
g)
magnetic field (Oe)
Cu
Co
(c)
-80
-60
-40
-20
0
20
40
60
80
-40000 -20000 0 20000 4000
Mag
netiz
atio
n (e
mu/
g)magnetic field (Oe)
Co
room
77K
(a)Fig. 6 Magnetic hysteresis
loops for a CoFe2O4,
b CuFe2O4 at 300 and 77 K,
c Co and Cu at 77 K
Table 3 The saturation magnetization, remnant magnetization, coercive field, squareness, anisotropy constant, roughness for CoFe2O4, CuFe2O4
at 300 and 77 K
Samples Ms (emu/g) Mr (emu/g) Hc (Oe) Mr/Ms Anisotropy const. K 9 104 Roughness (lm)
CoFe2O4 66.847 31.114 1641.3 0.465 11.429 1.2
CuFe2O4 22.063 11.648 1040.6 0.528 2.392 1.5
77 K
CoFe2O4 63.708 52.529 8656.2 0.825 57.445
CuFe204 25.605 14.103 1108.9 0.551 2.958
0
1
2
3
290 390 490 590 690 790 890 990
χ m(e
mu/
gm m
ole)
Temperature (K)
Co Cu
300 400 500 600 700 800 900 1000
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
Temperature (K)
dXm/d
T
-0.008
-0.007
-0.006
-0.005
-0.004
-0.003
-0.002
-0.001
0.000
0.001
dX m
/dT
Fig. 7 Magnetic susceptibility versus temperature for CoFe2O4 and CuFe2O4 nanoferrites. The inset shows the 1st derivative of magnetic
susceptibility with temperature
J Mater Sci: Mater Electron (2017) 28:241–249 247
123
4 Conclusion
1. The saturation magnetization depends on the rough-
ness, particle size and cation distribution of the
particles.
2. The nano-particles of Cu have small particle size
(29 nm) and low degree of agglomeration. While Co
nano-particles synthesized tend to be agglomerated
since it has comparable high particle size.
3. The saturation magnetization of cobalt ferrite is
approximately equal to 66.8 emu/g which is 67 %
larger than the value of 22.06 emu/g for copper ferrite.
4. The coercivity value at 77 K is found to be twice as
large as Hc at room temperature.
5. Co samples will be a guaranteeing hopeful for techno-
logical applications at or below room temperature.
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Co 2.57 4.5 832 830
Cu 0.8 2.5 821 790
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