Optical and magnetic properties of CuO/CuFe2O4 nanocomposites

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Journal of Materials Science:Materials in Electronics ISSN 0957-4522 J Mater Sci: Mater ElectronDOI 10.1007/s10854-013-1164-8

Optical and magnetic properties of CuO/CuFe2O4 nanocomposites

M. M. Rashad, D. A. Rayan &A. A. Ramadan

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Optical and magnetic properties of CuO/CuFe2O4 nanocomposites

M. M. Rashad • D. A. Rayan • A. A. Ramadan

Received: 11 December 2012 / Accepted: 26 February 2013

� Springer Science+Business Media New York 2013

Abstract CuO/c-CuFe2O4 nanocomposites have been

synthesized via the oxalate precursor route. Effect of syn-

thesis conditions on the crystal structure, microstructure,

magnetic and optical properties of the formed powders was

studied. The results indicated that pure CuO nanoparticles

were obtained from the oxalate precursor annealed at

600 �C for 2 h. However, substitution of Cu2? ion by Fe3?

ion (Cu1-XFeXO, where X = 0, 0.05, 0.1 and 0.2) led to

form of CuO/CuFe2O4 nanocomposites. The microstruc-

tures of the powders appeared as a monoclinic like shape.

Furthermore, the band gap energy of the obtained CuO

nanopowders was 1.41 eV and the value was slightly

decreased by Fe3? ion substitution. In addition, the formed

CuO particles had weak ferromagnetic characteristics.

However, the substitution Cu2? ion by Fe3? ion enhanced

the magnetic properties of the formed composite as the

result of increasing the CuFe2O4 phase formation. Hence,

the saturation magnetization was increased from 0.13 to

9.8 emu/g by increasing the Fe3? ion from 0 to 0.2.

1 Introduction

The focus on the correlation between the magnetic and

optical properties of magnetic-semiconductors composites

has a special attention in the recent years. Magnetic par-

ticles have the great potential applications in aircraft,

spacecraft, magnetic hard disks, telecommunication, mag-

netic recoding media and credit cards. On the other hand,

semiconductors have a wide range of applications in gas

sensing, catalysis, solar cells and electro-optical devices.

From this the point of view, copper oxide (CuO) as an

important p-type semiconductor with a narrow band gap

(1.2 eV), has been extensively studied because of its

diverse applications for heterogeneous catalysts, gas sen-

sors, optical switch, magnetic storage media, rectifiers,

lithium-ion electrode materials, field emission devices and

solar cells etc. [1–5].

However, the substitution of Cu2? ion by Fe3? ion leads

to form CuO/CuFe2O4 nanocomposite [6]. In particular,

copper ferrite has unique characteristics compared with the

other spinal ferrites. CuFe2O4 is known to exist in tetrag-

onal and cubic structures. Under slow cooling Cu-ferrite

crystallizes in a tetragonal structure with lattice parameter

ratio c/a of 1.06. Tetragonal Cu-ferrite phase has inverse

spinel structure with almost all Cu2? ions occupying

octahedral sublattice, whereas Fe3? ions divide equally

between the tetrahedral and octahedral sublattices. The

cations distribution in CuFe2O4 can be represented by

(CuxFe1-x)A(Cu1-xFe1?x)BO4, where x is the inversion

parameter and x = 0 and 1 stands for the inverse and

normal cases, respectively. The cubic structure is stable at

room temperature and transforms to tetragonal phase only

at a temperature of 360 �C and above due to Jahn–Teller

distortion. The distortion is directly related to the magnetic

properties. The cubic structure possesses a larger magnetic

moment than that of the tetragonal one, because there are

more cupric ions (Cu2?) at tetrahedral sites in cubic

structure as compared to that in the case of tetragonal

structure [7]. CuxFe3-xO4 has been chosen for its n-type

semiconducting property, as well as the possibility of

forming into nanocomposites thin films with CuO. By

M. M. Rashad (&) � D. A. Rayan

Central Metallurgical Research & Development Institute,

P.O. Box 87, Helwan 11421, Egypt

e-mail: [email protected]

A. A. Ramadan

Physics Department, Faculty of Sciences, Helwan University,

Helwan, Egypt

123

J Mater Sci: Mater Electron

DOI 10.1007/s10854-013-1164-8

Author's personal copy

changing the Cu and Fe contents, the material can be tuned

in a wide range of conductivities and altered from n- to

p-type [8].

The properties of the nanocomposites depend on the

microstructure which is related to the method of preparation.

The later plays a very important role with regard to the

chemical and structural properties of the composite. In fact,

the diverse available methods or routes to prepare magnetic-

CuO nanocomposites have been published. For example,

magnetic nanocomposites containing (NiFe2O4/CuO/FeO)

phases having particle size *17 nm were synthesized by a

sol–gel method [9]. Furthermore, CuO–CuFe2O4 nanocom-

posites have been synthesized through solid state reaction [6],

nitrate route [10] and sol gel method [3]. From our knowl-

edge, this is the first time for studying the optical and

magnetic properties of CuO–CuFe2O4 nanocomposite syn-

thesized via the oxalate precursor method. The oxalate pre-

cursor method involves the preparation of aqueous solution

containing cations, chelating of cations from solution by

adding carboxylic acid, followed by raising the temperature

of the solution until precursor formation. The precursor is

consequently calcined at low temperature, which is consid-

ered an advantage when compared to other methods men-

tioned earlier. The used method has similarities with the

combustion method, polymeric precursor method, acid sol

gel method (oxalate precursor, tartaric acid, lactic acid, etc.),

auto-combustion and also Pechini-type process (citrate pre-

cursor method). The carboxylic acid in this approach was not

only used to form stable complexes with starting metallic ions

but also as organic rich fuel. The process is simple, considers

an environmentally friendly method that offers scalability for

large scale production, uses low cost starting materials, low

synthesis temperature and yields homogeneous microstruc-

ture with narrow particle size distribution [11–13]. However,

it is necessary to enhance the magnetic properties of CuO for

magnetic storage media. Furthermore, the presence of

CuFe2O4 magnetic material during CuO as application pho-

tocatalyst helps in the regeneration of the catalyst after the

processing which can be easily removed from the solutions

[7]. The aim of the present work is to investigate the synthesis

of CuO–CuFe2O4 nanocomposites powders via the oxalate

precursor pathway. Moreover, the change in phase compo-

sition, microstructure, optical and magnetic properties of the

obtained materials is also investigated.

2 Experimental

The oxalate precursor method was applied for the prepa-

ration of CuO/CuFe2O4. Chemically grade copper chloride

CuCl2.2H2O, anhydrous ferric chloride FeCl3, and oxalic

acid H2C2O4 were used as starting materials. A certain

amount of oxalic acid related to stoichiometric ratio of

Cu2? ion was added gradually into the aqueous solution.

Than, the solution was stirred gently and evaporated at

80 �C till a clear, viscous gel was obtained, and then dried

at 110 �C for 24 h. The dry precursors were thermally

treated at a rate of 10 �C/min in static air in muffle furnace

with different maximum holding temperatures ranging

from 400 to 900 �C for time 2 h. To explore the effect of

substitution of Fe3? ion substituted CuO on the crystal

structure, microstructure and magnetic properties of the

formed particle, experiments were conducted at 600 �C for

2 h with different of Fe3? ion (CuXFe1-XO from 0 to 0.2)

where the molar ratio between the metal ion to oxalic acid

was 1:1 according to the following equations:

1� XCu2þ þ XFe2þ þ C2O2�4 CuC2O4ð Þ1�X FeC2O4ð ÞX

ð1ÞCuC2O4ð Þ1�X FeC2O4ð ÞXCuOþ CuFe2O4 þ 2CO2 þ 2CO

ð2Þ

The crystallite phases present in the different annealed

samples were identified by X-ray diffraction (XRD) on a

Brucker axis D8 diffractometer with crystallographic data

software Topas 2 using Cu-Ka (k = 1.5406 A) radiation

operating at 40 kV and 30 mA at a rate of 2�/min. The

diffraction data were recorded for 2h values between 20� and

80�. Fourier transform infrared spectroscopy (FTIR) was

conducted on a Thermo Electron Magna 760. Transmission

electron microscopy (TEM) of the particles were performed

using a JEOL-JEM-1230 microscope. The UV–VIS

absorption spectrum was recorded by a UV–VIS–NIR

spectrophotometer (Jasco-V-570 spectrophotometer, Japan).

The magnetic properties of the formed powders were

measured at room temperature using a vibrating sample

magnetometer (VSM; 9600-1 LDJ, USA) in a maximum

applied field of 16 kOe. From the obtained hysteresis

loops, the saturation magnetization (Ms), remanence mag-

netization (Mr) and the coercive field (Hc) were

determined.

3 Results and discussion

XRD patterns of the formed precursors using oxalic acid

molar ratio 1 related to Cu2? ions then annealed at different

temperatures from 400 to 900 �C for 2 h are given in

Fig. 1. It is clear that increasing the temperature led to

increase the crystallinity of copper (II) oxide CuO phase

formation. However, at low annealing temperature 400 and

500 �C, an impurity secondary phase of orthorhombic

eriochalacite CuCl2 (JCPDS # 76-0569) was formed with

tenorite monoclinic CuO phase ((JCPDS # 72-0629).

However, increasing the annealing temperature from 600 to

900 �C, single monoclinic CuO phase was indexed.


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To explore the effect of Fe3? ion and its impact on the

crystal structure of the CuO powders, XRD diffraction

patterns of the as-made samples with different Fe3? ion

molar ratios from 0 to 0.2 and annealed at 600 �C for 2 h

are shown in Fig. 2. The results illustrated that sharp and

intensive peaks characteristics related to cubic copper

ferrite CuFe2O4 (JCPDS # 77-10) with monoclinic CuO

with increase the iron substitution from 0.1 to 0.2 were

detected. The qualitative analysis from XRD patterns data

for the main peaks of two phases indicates that CuFe2O4

phase ratio was increased from 5 to 10 % with increasing

Fe3? ion substitution from 0.1 to 0.2. The obtained results

have different approaches than the previous results pub-

lished elsewhere the previous work in which a-Fe2O3 is

formed as an impurity phase with CuO and CuFe2O4

phases for CuFe2O4 [14], CuxFe3-xO4 [15] and

CuyMnxFe3-y-xO4 [16] by synthesized oxalate acid pre-

cursor pathway. The main reasons for such difference was

the molar ratio of Fe3? ion for spinel ferrite formation must

be 2. However, in the present work, the highest Fe3? ion

content was 0.2. Furthermore, there is a syntheses pro-

cessing for the previous work difference for the proceeding

in which oxalic acid solution was added into the metal salts

in alcoholic medium. Then, the mixed oxalate were slowly

decomposed under air flow and then treated in controlled

atmosphere H2/N2/H2O at 700 �C for 4 h [14–16].

The crystallite size of the formed particles were given

based on Deby-Scherrer equation of the most interse peak

estimated from XRD patterns. The crystallite size of the

CuO nanoparticle was decreased by increasing the Fe3? ion

molar ratio as the result of increasing the crystallinity of

CuFe2O4. The changes of the lattice parameters and cell

volume of the formed nanocomposites due to Fe

substitution ratios were summarized in Table 1. It can be

seen that the slightly changes in the lattice parameter and

unit cell value were observed as the amount of Fe3? ion

increased.

Figure 3 shows TEM micrographs of the pure CuO phase

obtain at annealed temperature 600 �C for 2 h compared

with the composite forms with Fe substituted CuO at molar

ratios 0.05 and 0.2. It is noticed that the formed CuO nano-

powders exhibit a regular morphology consisting a large

obtuse angle and a small acute angle, which more likely stem

for the monoclinic nature of tenorite CuO as shown in

Fig. 3a. The average particle size of the obtained nano-

powders was*45 nm. The microstructure of 0.05 and 0.2 Fe

molar ratios substituted CuO have insignificant change as

depicted in Fig. 3b, c. Furthermore, the average particles size

of the CuO was decreased with increasing the Fe3? substi-

tution whereas the average particle size of the Fe substituted

CuO with 0.2 ratio was *42 nm.

The FT-IR spectra for CuO/CuFe2O4 nanocomposites at

different Fe molar ratios were shown in Fig. 4. The results

confirmed that pure CuO was three broad absorption peaks at

582, 535 and 489 cm-1, assigned to the stretching vibrations

of Cu–O bond in the monoclinic CuO [17, 18]. However,

with Fe molar ratio 0.2, two bands were observed. Generally,

for spinel ferrite, the band t1 around 600 cm-1 is attributed

to stretching vibration of tetrahedral complexes and t2

around 400 cm-1 to that of octahedral complexes. It can be

seen that the observed band at 585 cm-1 in the spectrum of

CuFe2O4 is attributed to the stretching vibration of tetrahe-

drally coordinated Fe3?–O2- bonds [19, 20].

The optical properties of the formed particles were

examined using UV–Vis spectrophotometer and the results

are indicated in Fig. 5. The results revealed that with

Fig. 1 XRD patterns of

produced copper oxide CuO

powders at different annealed

temperatures from 400 to

900 �C for 2 h


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increase in the wave length longer than 240 nm, an

increase in the transmittance absorbance was observed

which a characteristic peak of monoclinic CuO [21]. The

absorption coefficient for CuO nanoparticles was given

using the following equation:

ðahvÞm ¼ hv� Eg ð3Þ

where a is the absorption coefficient, ht is the photon

energy, Eg is the band gap energy, m = 1/2 or 3/2 for

indirect allowed and indirect forbidden transitions, and

m = 2 or 3 for direct allowed and direct forbidden

transitions. The band gap energy was estimated by

plotting (aht)2 of the polycrystalline CuO against the

photon energy (ht), as shown in Fig. 6. The band gap

energy was determined by extrapolating the absorption

coefficient (a) to zero. The absorption (A) is converted to

the absorption coefficient using the following relationship

[21, 22]:

a ¼ ð2:303� 103ÞAqlc

ð4Þ

where A is the absorption of the sample, q is the density of

CuO (6.51 g/cm3), l is the length (1 cm), and c is the

concentration of the CuO nanocrystals (20 g/cm3). A linear

correlation between (aht)2 and ht implies the direct tran-

sition nature of CuO as shown in Fig. 6. The direct tran-

sition nature of CuO agree with the previous published

work in the literature [23–25]. The obtained band gap

energy of 1.41 eV was for the pure CuO nanoparticles. The

value was higher in compared with the CuO bulk value of

Eg (1.2 eV). However, the value was lower than the given

for CuO (Eg = 2.75 eV) synthesized via a thermal

Fig. 2 XRD patterns of

produced CuO powders with

different Fe molar ratios

annealed at 600 �C for 2 h

Table 1 Variation of crystallite size, lattice parameters and cell volume of CuO–CuFe2O4 nanocomposites formed with different Fe molar ratios

Sample Phases Cry. size (nm) a (A�) b(A�) c(A�) Cell volume (A�3)

CuO pure CuO 65.3 2.673 3.418 2.908 26.2

Cu0.95 Fe0.05O CuO 54.3 2.674 3.422 2.907 26.24

Cu0.90 Fe0.10O CuO CuFe2O4 47.3 2.672 3.421 2.909 26.22

7.9 8.407 – – 594.21

Cu0.85 Fe0.15O CuO CuFe2O4 45.1 2.674 3.421 2.907 26.21

15.4 8.409 – – 594.54

Cu0.80 Fe0.20O CuO CuFe2O4 42.4 2.674 3.42 2.902 26.18

19.4 8.409 – – 594.55


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decomposition of CuC2O4 at 400 �C [23], and the produced

CuO (2.43 eV) via the microwave irradiation [26]. The

change in the results may be attributed to the enhancement

of the quantum confinement effect resulting from the

decrease in the dimensional structure and the size of the

nanoparticles [26]. On the other hand, the band gap energy

Fig. 3 TEM micrographs of

iron doped cupric oxide

nanopowders different Fe molar

ratios a 0, b 0.05, c 0.2 annealed

at 600 �C for 2 h

Fig. 4 FT-IR absorbance

spectrum with and without Fe

substituted copper oxide

nanopowders


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for Fe substituted CuO is slightly decreased from 1.36 to

1.38 eV. The direct band gap positioned near the optimal

value of the sun spectrum and the high energy of con-

duction band CB, giving the photo electrons a strong

reducing ability. Moreover, it is low cost and the constit-

uent elements Cu and Fe are the most attractive if we take

toxicity into account. The produced CuO–CuFe2O4 was

used to get efficient hydrogen production where a Eg

around the ideal value of *1.4 eV needed for terrestrial

applications [27].

The magnetization of the produced powders was per-

formed at room temperature under an applied field of 15 kOe

and the hysteresis loops of the powders were obtained. Plots

of magnetization (M) as a function of applied field (H) for of

the nanocomposites synthesized at different Fe molar ratios

are shown in Fig. 7 and the corresponding data are collected

in Table 2. The results showed that ferromagnetic properties

with clear hysteretic behavior. The saturation magnetic

moment and the coercive field Hc at room temperature were

*0.13 emu/g and 127.24 G, respectively. The value of

Fig. 5 UV-visible

transmittance spectrum of iron

doped cupric oxide

nanopowders with different Fe

molar ratios from 0.0 to 0.2

annealed at 600 �C for 2 h

Fig. 6 Band gap energy of

CuO–CuFe2O4 nanocomposites

with different Fe molar ratios

from 0 to 0.2 annealed at

600 �C for 2 h


123


saturation magnetization is higher than published before for

straw CuO which was 1.2 9 10-4 [28]. The real reason of

ferromagnetism are supposed only have relationship with the

unpaired electrons spin resulting from the oxygen vacancies

at the surfaces of the nanostructure. As the principle, the

oxygen at the surface escape from the bondage of

the chemical bond because of heat, light and so on, then the

unpaired electrons show the abnormal spin phenomenon to

come out the magnetism. Shang et al. [28] suggested that the

unpaired electron spins responsible for ferromagnetism in

the CuO nanoparticles have their origin in the oxygen

vacancies, especially on the surfaces of the oxide nanopar-

ticles. Furthermore, the results may be explained on the basis

of electrons trapped in oxygen vacancies (F center) are

polarized to give room-temperature ferromagnetism [28].

On the other hand, the variation of saturation magnetization

(Ms), coercivity (Hc) and remanence magnetization (Mr) as

the function of the different substituted Fe ratios is observed

as shown in Fig. 7. The values of Ms, Mr and Hc were

increased drastically with increase the Fe3? ion ratio. High

saturation magnetization (9.8 emu/g) was achieved with

increasing the Fe molar ratio to 0.2. The value is attributed to

the formation of cubic copper ferrite phase with a high

crystallite size at higher Fe ratio causing a significant

increase in the values of the magnetic parameters [29].

4 Conclusion

Nanostructures of CuO/c-CuFe2O4 composite have been

fabricated using the oxalate precursor technique. The

results revealed that a pure phase of cupric oxide CuO

nanoparticles was formed for the sample annealed at

600 �C for 2 h with undoped Fe sample. The crystallite

size of the produced CuO powders was 47.4 nm. The Fe3?

ion substitution of Cu2? ion led to form CuO/CuFe2O4

nanocomposites. From XRD profile, CuFe2O4 phase ratio

in the composite was *5 and 10 % with increasing the

substitution of Fe3? ion ratio to 0.1 and 0.2, respectively.

The microstructures of the obtained composites were

change Fe3? by substitution. The band gap energy of CuO

was slightly decreased with Fe3? substitution from 1.41 to

1.38 eV. High saturation magnetization (Ms = 9.8 emu/g)

was achieved with doped Fe3? ion ratio 0.2. For instance,

the coercive field Hc increases with increasing of Fe3?

molar ratio as the results of the formation of c-CuFe2O4

phase.

Fig. 7 M-H hysteresis loops of

the produced CuO–CuFe2O4

nanocomposites at different Fe

molar ratio from 0.05 to 0.2.

The top-right inset shows the

M-H hysteresis loop of pure

CuO powders

Table 2 Magnetic properties of CuO–CuFe2O4 nanocomposites

formed with different Fe molar ratios from 0 to 0.2 annealed at

600 �C for 2 h

Fe doped Magnetic properties

Ms, emu/g Mr, emu/g Hc, Oe

0.00 0.13 0.01 127.9

0.05 2.06 0.40 10.1

0.10 5.23 1.08 32.4

0.15 8.10 1.88 59.6

0.20 9.82 2.22 79.1


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Documents

Optical and magnetic properties of CuO/CuFe2O4 nanocomposites