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

galila@sci.cu.edu.eg

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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