Influence of copper ions on structural and non-linear optical properties in manganese ferrite nanomaterials

Optical Materials 73 (2017) 428e436

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Influence of copper ions on structural and non-linear optical properties in manganese ferrite nanomaterials S. Yuvaraj, N. Manikandan, G. Vinitha* Division of Physics, School of Advanced Sciences, VIT University, Chennai Campus, Chennai 600127, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 6 July 2017 Received in revised form 17 August 2017 Accepted 18 August 2017

A series of Mn1-xCuxFe2O4 (x ¼ 0, 0.15, 0.30, 0.45, 0.60 and 1) particles were prepared using chemical coprecipitation method with metal nitrates as precursor materials. Samples were synthesized under various annealing temperatures and 800  C was found to be the optimal temperature for phase formation. Powder XRD analyses confirm the formation of spinel manganese ferrites along with the a-Fe2O3 phase which got reduced with increase in copper concentration. Samples were characterized using spectroscopic and microscopic techniques. UV-Diffuse reflectance spectroscopy was employed to calculate the band gap which varied between 1.51 eV and 1.83 eV. HR-SEM images reveal the spherical nature of the particles. Ferromagnetic nature of these materials was confirmed from vibrating sample magnetometer (VSM) measurements. Z-scan technique was employed to measure the non-linear optical properties. The non-linear refraction, non-linear absorption and non-linear susceptibility are found to be of the order of 108 cm2/W, 104 cm/W and 106 esu respectively. The samples showed a defocusing effect which was utilized to explain the optical limiting behavior at the same wavelength using the continuous-wave laser beam. The results show that these materials have potential for exploitation towards device applications like optical limiting and switching. © 2017 Elsevier B.V. All rights reserved.

Keywords: Mn-Cu ferrites Morphology Bandgap Magnetic properties Z-Scan Optical limiting

1. Introduction The current trend in research deals with nanomaterials which are widely used for technological applications. In general, metaloxide nano particles which vary from their bulk particles draw considerable interest due to their unique properties [1]. Since produced by Snock in 1935, nano structured ferrites especially spinel ferrites are examined for their extraordinary features of electrical, optical and structural characteristics [2,3]. The crystal structure of Spinel ferrite is AB2O4, where A denotes tetrahedral site and B denotes octahedral site. The unit cell of spinel ferrites comprises of 32 octahedral sites and 64 tetrahedral sites. Lattice consisting of 8 tetrahedral sites filled by divalent metal ions and 16 octahedral sites filled by trivalent iron ions aid in maintaining electrical neutrality in these samples [4]. Manganese ferrites possess impressive properties such as outstanding chemical stability, large saturation magnetization, prominent magneto e crystalline anisotropy and elevated mechanical hardness that makes them unique among all the spinel

* Corresponding author. E-mail address: [email protected] (G. Vinitha). http://dx.doi.org/10.1016/j.optmat.2017.08.027 0925-3467/© 2017 Elsevier B.V. All rights reserved.

ferrites [5]. Manganese ferrites are frequently used for microwave and magnetic recording applications owing to their excellent magnetic behavior [6]. These samples were also found to show good electromagnetic absorbent properties leading to their application in wide areas [7]. Consequently, it is reasonable to investigate MnFe2O4 nanomaterials for various other applications. Numerous synthesis approaches have been used for the preparation of MnFe2O4 nanocrystals, such as microwave-assisted ball mill [8], sono chemical [9], hydrothermal [10], sol-gel auto combustion [11], ultrasonic [12], solvothermal [13], thermal decomposition [14] and co-precipitation [15]. Among all the wet chemical methods in use, co-precipitation method is most preferable in view of the fact that it is more cost effective, non-hazardous and involves low level of toxic materials with high productivity of ferrite nanoparticles [15]. Recent research has shown that nanomaterials show better nonlinear effects compared to their bulk counterparts [16]. These low dimensional materials with large nonlinear responses can be used in various applications like photocatalysis and optical limiting [17,18]. Magnetic nanomaterials have attracted substantial attention as optical limiters since the optical properties of such optoelectronic devices are controllable by an external stimulus such as magnetic field [19]. Optical nonlinearities in ferrites are relatively

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unexplored compared to metals, semiconductors and organometallic compounds [20]. Modifications in optical nonlinearity caused by the inclusion of different transition metals into a spinel ferrite system would be of considerable interest owing to their applications in the field of optics. Z-scan is an accurate system to find out the nonlinear optical response of the material. Closed aperture scan provides information about both nonlinear refraction and absorption, while the open aperture yields the values pertaining only to nonlinear absorption of the materials [21]. This nonlinearity observed in materials is due to their intensity-dependent absorption and refraction [22]. In this paper, Mn1-xCuxFe2O4 ferrite powders with x ¼ 0, 0.15, 0.30, 0.45, 0.60 and 1.0 were prepared using chemical coprecipitation route and their nonlinear properties were studied. To the best of knowledge of the authors, it is the initial article which reports the optical nonlinearity of Cu2þ substituted Mn ferrites and their device realization. 2. Samples 2.1. Materials For the chemical co-precipitation route, manganese (II) nitrate monohydrate (Min. 98%, Himedia), copper (II) nitrate tetrahydrate (Min. 98% Himedia) and iron (III) nitrate hexahydrate (Min. 98%, Himedia) were employed as starting materials. Sodium hydroxide was taken as precipitating agent. To make the entire solution, double distilled water was used and all received chemicals were used without any further refinement. 2.2. Synthesis of nanocrystalline Mn1-xCuxFe2O4 ferrite The proposed nano-sized ferrites were prepared by chemical coprecipitation route, using pure materials: (0.1 M) Manganese (II) nitrate, (0.1 M) Copper (II) nitrate, (0.1 M) Iron (III) nitrate. The ratio between Fe and MnCu was kept at 2:1 respectively. All the starting pure materials were dissolved one by one in double distilled water and mixed together to form aqueous solution. The aqueous solution of 3 M NaOH was slowly poured into the mixed solution under stirring at a temperature of 100  C. pH was maintained at 11e12 for all the cases to make the entire metal cations precipitated. The mixture was then heated at 120  C for one and half an hour before cooling down slowly to room temperature. Black precipitates were obtained in this routine. To eliminate impurities, the product was frequently washed by using double distilled water and ethanol. Hot air oven maintained at 100  C for 24 h was used to dry the samples. Finally the black color powder was obtained which was annealed at 800  C for 5 Hours. The same method was adopted for all the compositions. 3. Results and discussion 3.1. Phase analysis XRD structural pattern of the analyzed samples are as represented in Fig. 1. According to the XRD results of synthesized samples, one can state that the combination of a-Fe2O3 and MnFe2O4 phase exists for the concentration x ¼ 0 (Fig. 1(a)). The sample x ¼ 0.15 (Fig. 1(b)) clearly shows the bragg reflection peaks related to the hkl planes of (220), (311), (222), (400), (422), (511) and (440) indicating the structural formation of MneCu spinel ferrites along with the cubic symmetry which is marked as ‘C’ and has been confirmed with JCPDS (Card No: 74-2072). The minor peaks with the symbol which is marked ‘*’ is related to a-Fe2O3 (as per JCPDS data 84-0307). As reported in Ref. [23], if metal nitrates are used as

Fig. 1. Phase diagram of (a) MnFe2O4 (b) Mn0.85Cu0.15Fe2O4 (c) Mn0.70Cu0.30Fe2O4 d) Mn0.55Cu0.45Fe2O4 (e) Mn0.40Cu0.60Fe2O4 and (f) CuFe2O4 sample.

raw materials, it needs high annealing temperature of around 1200  C to form pure phase. It was noted that when the sample was annealed at more than 500  C, Cu doped manganese ferrite exhibits few minor impurity peaks which demonstrates the decomposition of the ferrites to aFe2O3 phase. It was observed that when the annealing temperature is made higher than 900  C, the secondary minor peaks start to slowly disappear and it may completely disappear when the temperature is elevated beyond 1200  C [24]. For the composition x ¼ 1.0, which is a copper ferrite, pure phase is obtained. The degree of crystallinity is determined from the diffracted peak of nano ferrite at the hkl plane (311) which exhibits the highest intensity. The effective crystallite size of Mn1-xCuxFe2O4 samples were evaluated via applying the DebyeeScherrer formula,

L¼

0:89l bcosq

Where q is the diffracted angle of the highest intensity peak, b is the full width at half maxima (FWHM) and l is wavelength of the Xray. The calculated results exposed that the pure MnFe2O4 possesses smaller crystallite size (21.72 nm). Addition of copper ions showed variations in particle size ranging from 12 to 51 nm (See Fig. 2). The range of effective crystallite size expresses the fluctuation with raising copper percentage in manganese ferrites. In 2015, similar kind of findings was recorded by Appas et al. for zinc doped manganese ferrites [44]. X- ray diffraction data is used to find out the lattice parameter (a) from the formula,

 1 1
2 2 2 h ¼ þ k þ l a2 d2 Table 1 presents the estimated amount of lattice constant (a) and crystallite size for all the Cu2þ concentrations. Increase of copper ions in MnFe2O4, gradually reduced the lattice constant from 8.545 Å to 8.420 Å. The relative ionic radius describes the reason behind the continuously decreasing rate of lattice constant with linear increase in the copper percentage. The divalent manganese ions contain larger ionic radius (0.63 Å) compared to divalent copper ionic

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defects give rise to huge and unequal agglomerated nanocrystals in Cu doped Mn ferrites. The surface morphology have a size distribution over 45e75 nm, which is well matched with the calculated crystallite size of XRD.

3.3. Energy dispersive X-ray (EDX) analysis

Fig. 2. Growth of the crystallite size and lattice constant of Mn1-xCuxFe2O4 samples.

radius (0.57 Å). The systematic decrease in the values of lattice constant is accomplished by the alternation of bigger Mn2þ ions on behalf of lesser Cu2þ ions in nano MnFe2O4, thus obeying Vegard's law [26]. Similar type of results were found by Zhuang et al. where increasing the doping ratio of Zn2þ along with lesser ionic radius manganese nano particles, cause progressive decrease in the parameter of lattice constant [27]. 3.2. Morphology (HR-SEM) analysis The external surface morphology of Mn1-xCuxFe2O4 substances at 0.15 and 0.45 concentrations denoted by the HR-SEM picture is as illustrated in Fig. 3. Elevated percentage in copper concentrations makes observable variation in the surface spherical morphology. It is perceived that the influence of annealing, synthesis route and

The energy dispersive X-ray studies and their results offer detailed information about chemical composition of nano structured Mn1-xCuxFe2O4 (x ¼ 0.15, 0.45). The existence of Mn2þ, Cu2þ, Fe3þ and O2þ elements is proved in the EDX spectrum (Fig. 4). The stoichiometric ratio (2:1) of copper substituted manganese ferrites is very near to the estimated amount of atomic percentage which is revealed from the quantitative report of EDX spectrum. As a result, the stoichiometry in preparation is well matched with the atomic ratio of experimental quantity. In addition the peak at 2.1 KeV is due to presence of Au which was included during sample preparation (by sputtering).

3.4. Diffuse reflectance spectra (DRS) analysis The variation in the optical band gap induced by Cu concentration was studied by UV-Diffuse reflectance spectroscopy. Tauc relation was applied to evaluate the bandgap values of Mn-Cu ferrites [28]. In general, the reflectance data are transferred by utilizing Kubelka-Munk function. The optical absorption coefficient can be calculated by Kubelka-Munk function.

a ¼ FðRÞ ¼

ð1  RÞ2 2R

where, R is the reflectance; a is the absorption coefficient, F(R) is the function of KubelkaeMunk. Thus Tauc relation,

Table 1 The structural and optical parameters for Mn1-xCuxFe2O4. Cu concentrations

Crystallite size (nm)

Lattice constant (Å)

Bandgap (eV)

Linear refractive index

Linear absorption coefficient (at 532 nm)

0.00 0.15 0.30 0.45 0.60 1.00

21 20 31 48 32 12

8.5452 8.4498 8.4673 8.4467 8.4235 8.4201

1.53 1.83 1.60 1.52 1.51 1.72

1.127 1.147 1.211 1.213 1.194 1.144

1.947 1.87 1.618 1.596 1.666 1.883

Fig. 3. HR-SEM picture of (a) Mn0.85Cu0.15Fe2O4 (b) Mn0.55Cu0.45Fe2O4.

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Fig. 4. EDX spectrum of (a) Mn0.85Cu0.15Fe2O4 (b) Mn0.55Cu0.45Fe2O4.

 n FðRÞhv ¼ A hv  Eg where n ¼ 1/2 and 2 for indirect and direct transitions, providing indirect and direct band gaps respectively [29]. Fig. 5 shows the graph of hy versus (F(R)hy)2 and the energy gap (Eg) attained via the

intercept for the samples (x ¼ 0.15, 0.30, 0.45 and 0.60). Table 1 presents the evaluated optical band gaps for Mn1-xCuxFe2O4 (x ¼ 0.15, 0.30, 0.45, 0.60) nanoparticles to be 1.83, 1.60, 1.52 and 1.51 eV respectively. Hence, blue shift occurred while increasing Cu concentrations and it obviously exposed the reduction in the band gap. In the agglomerated primary nanoparticles, the utmost defects

Fig. 5. UVeDRS spectrum of (a) Mn0.85Cu0.15Fe2O4 (b) Mn0.70Cu0.30Fe2O4 (c) Mn0.55Cu0.45Fe2O4 (d) Mn0.60Cu0.40Fe2O4.

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in the boundary and outer surface stimulate more new sub-bandgap energy levels which are the reason behind the decrease in the value of energy band gaps [30]. Owing to quantum confinement effects which evolved from lesser dimension range, energy gap (Eg) of the Mn1-xCuxFe2O4 nanoparticles shifted with the reduction in the size of crystals [31,32]. 3.5. FT-IR spectral analysis Fig. 6 reveals the mid-IR (4000-400 cm1) FT-IR spectra for pure and Cu substituted MnFe2O4 spinels. The formation of spinel ferrites was confirmed from the tetrahedral site of Fe3þeO2- causing intrinsic stretching vibrations at higher frequency band near 590 cm1 and the octahedral site of M2þeO2- drive metal stretching vibrations at lower frequency band in the region of 448 cm1 [25]. The presence of the water molecules on the surface of spinel ferrites make stretching vibrations of OeH groups at broad frequency band close to 3444 and 1640 cm1 [33]. As a result of atmospheric CO2, bending vibration of C]O exists through the weak frequency band at 2324 cm1 [34]. The frequency band nearby 1370 cm1 and 1112 cm1 is for the stretching and bending vibrations of CH3 molecules respectively [35]. 3.6. Photoluminescence spectra (PL) analysis Information regarding impurity states, defect sites and band gap energy (Eg) are offered by photoluminescence (PL) spectra. Emission peak appears once when electrons are struck by optical light and excited electron comes back along with radiative relaxation to the ground level [37]. As shown in Fig. 7, two most important peaks are proclaimed by the PL spectrum, one peak at upper wavelength region 484 nm (2.56 eV) related to the blue emission and the another one at lower wavelength range 420 nm (2.95 eV) associated to violet emission. The minor peak at 420 nm has lower intensity compared to the foremost peak at 484 nm. Hence, the aspects of Defect Level Emission (DLE) is conferred upon the emission peat at 484 nm and Near Band Emission (NBE) features of Mn-Cu ferrites is attained through the emission peak at 420 nm. The prominent peak at greater wavelength (484 nm) while compared to the band edge emission (424 nm) belongs to the defect levels which occupy oxygen spot [36]. In PL Spectra, the band

Fig. 7. Photoluminescence spectrum of Mn1-xCuxFe2O4 samples.

edge emission peak is shifted from 420.07 nm to 415.26 nm with increase in Cu2þ content. The entire emission peak intensities for all the samples gradually reduced when Cu2þ content into MnFe2O4 is increased. Extra energy levels between the valence band and conduction band are due to the intrinsic defects and this ascribed to the decrease in peak intensity [38]. 3.7. Magnetic properties Fig. 8 depicts M  H loops of Mn0.55Cu0.45Fe2O4 ferrite sample taken using a VSM at room temperature. Magnetic Coercivity (Hc132.72 Oe), Magnetic Saturation (Ms- 45.4 emu.g1) and Remanance (Mr- 5.94 emu.g1) values of the Mn0.55Cu0.45Fe2O4 ferrite sample shows its strong ferromagnetic behavior. As stated by Neel's theory, the enormous amount of magnetization is attained while trivalent cations (Fe3þ) are spread over the octahedral positions and bivalent cations (Mn2þ, Cu2þ) reside in the tetrahedral sites of the spinel lattice [39]. The enhancement of crystallinity furnished with good magnetization exhibits excellent MS value which is in correlation with the phase formation [40]. As shown in Fig. 1(d), phase formation for Mn0.55Cu0.45Fe2O4 is obtained with good intensity. 3.8. Nonlinear studies

Fig. 6. FTIR Spectrum of (a) MnFe2O4, (b) Mn0.85Cu0.15Fe2O4, (c) Mn0.70Cu0.30Fe2O4, d) Mn0.55Cu0.45Fe2O4, (e) Mn0.40Cu0.60Fe2O4 and (f) CuFe2O4.

Excellence of Z-Scan method [41] comes from the superior feature that it not only gives the sign of nonlinearity of the sample, but also the nonlinear absorption coefficient (b) and nonlinear index of refraction (n2). Real part of third order susceptibility [Rec(3)] is directly proportional to n2 and the imaginary part [Imc(3)] is proportional to b. Diode pumped 532 nm CW Nd:YAG Laser (Coherent Compass™ 215M-50) focused via the lens of 3.5 cm focal length was utilized for nonlinear characterization. The 1.48 mm is the Rayleigh length and the laser beam waist at the focus is 15.84 mm. Mn1-xCuxFe2O4 (x ¼ 0, 0.15, 0.30, 0.45, 0.60 and 1.0) ferrite powders dispersed in ethylene glycol (at around 63% transmittance) was taken in a 1 mm cuvette and was translated along the axial path of the propagation of laser beam. Photo detector fed to the digital power meter (Field master GS-coherent) was employed to collect the transmitted laser beam passing by far field aperture. The aperture was interchanged by a lens to receive the complete transmitted laser beam which is passed through the

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sample for open aperture Z-scan. Fig. 9 shows the closed aperture, open aperture and ratio between the closed-to-open Z-scan transmittance. Closed aperture Zscan provides the normalized transmittance data as peak followed by valley denoting negative nonlinear index of refraction that happens due to self defocusing. The localized temperature rise in the sample leads to change in refractive index [42,43]. The variation among the normalized peak and valley transmittance (Tp  Tv) gives the value of DTp-v. The function jDfoj is used to evaluate the difference from

DTpv ¼ 0:406ð1  SÞ0:25 jDfo j where Df0 - on-axis phase shift at the focal point. Linear transmittance (S) from the aperture is estimated through


. S ¼ 1  exp  2 r 2 a u2 a

Fig. 8. VSM hysteresis curve of Mn0.55Cu0.45Fe2O4 sample.

where ra stand for the aperture radius and ua represents the radius of laser spot at aperture. The 3rd order index of nonlinear refraction is associated to the

Fig. 9. (a) Closed aperture (b) open aperture (c) ratio of closed to open aperture z-scan.

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on-axis phase shift by,

    Df0  ¼ kn2 Leff I0 where Leff ¼ ð1  eaL Þ = a, Here, I0 is the laser beam intensity at focal point of z ¼ 0, a is the linear absorption coefficient, k is the wave number (k ¼ 2p/l), L is the sample length and a is the linear absorption coefficient. [b] achieved from the data of open aperture Z-scan was applied to calculate the [Imc(3)] from the equations:

b$Io $Leff

qo ðzÞ ¼ 



2

1 þ ZZ 2 o

b¼

pffiffiffi 2 2$DT Io $Leff

ZR ¼ ku20/2 is the diffracted beam length, u0 is the radius of beam waist at the focus. The value of [Rec(3)] and [Imc(3)] discovered from [b] and index of nonlinear refraction (n2) which is observed by the experiment and the equations are,

Rec3 ðesuÞ ¼ 104

Im c3 ðesuÞ ¼ 102

εo c2 n2o

p

 n2

cm2 W

 (1)

εo c2 n2o l
cm b W 4p2

(2)

where, c is the velocity of light and ε0 is the permittivity at vacuum. Following equation is used to find out the total amount of c(3)

 

2

2 1=2  3 þ Im c3 c  ¼ Re c3

order to vary the input power, a polarizereanalyzer combination (PA) was used. At low level input intensities, the transmitted output intensity shows linear variations with the incident input intensity and with more increase in the input power, the transmitted intensity attains a plateau and gets saturated at a point defined as the limiting amplitude [46]. As seen from Fig. 10, the limiting amplitude decreases which confirms the increase in limiting efficiency with increase in the dopant concentration. The main parameter of the OL materials such as the optical limiting thresholds were found to be 9.3, 4.9, 3.5, 1.72 and 0.66 mW for Cu concentrations of 0.00 (MnF), 0.15, 0.30, 0.45 and 0.60 respectively. Addition of Cu2þ ions enhances the value of optical power limiting threshold in manganese ferrites. In general, the state of charge transfer (CT) among 3d orbital of Fe3þ ions and 2p orbital of O2þ ions influences the optical behavior of transition-metal ferrites [47]. Hence self-trapping of CT mechanism is utilized to describe the variation of optical behavior and that kind of mechanism is controlled through the lattice strain. Introducing the foreign Cu2þ atoms inside the manganese ferrites leads to structural deformation and induces lattice strain in the crystalline nature. Injected Cu2þ ions may fill octahedral or tetrahedral positions based on inverse or normal spinel system. Selftrapping of CT transition is enhanced by induced lattice strain and reflects through the elevated life time in excited state. As a consequence of this effect, significant changes occur in nonlinear absorption coefficient [b]. Therefore, it is concluded that the phase transitions [48] from inverse to normal spinel (which indicate the presence of more Fe3þ ions in octahedral site) improve the efficiency of the optical limiting devices and higher concentrations of Cu2þ ions expose enhanced nonlinear absorption and limiting threshold as demonstrated in Table 3.

(3)

Table 2 shows the characteristic features of nonlinearity which was determined by the Z-scan system. It is observed that the nonlinearity of manganese ferrite nanoparticles increases with increase in copper dopant percentage. In opto-electronic industry, these kind of third ordered optical nonlinearity materials with appreciable value is applied in electro optical modulator, data storage and acquisition, optical telecommunication system, optic signal conversion, in particularly optical power limiting devices [45]. The results prove that these particles have potential to be exploited for device applications like optical limiting or optical switching. 3.9. Optical limiting (OL) studies The nonlinearity exhibited by these samples has been exploited for devising optical limiters. The experimental setup to demonstrate the optical limiting of the laser beam under CW laser illumination is very similar to the standard Z-scan. Additionally, in

Fig. 10. Optical limiting characteristics of Mn1-xCuxFe2O4 samples.

Table 2 Third order nonlinear parameters of Mn1-xCuxFe2O4. Cu (x value)

n2  10

0.00 0.15 0.30 0.45 0.60 1.00

9.09 10.71 10.18 10.24 10.78 9.38

8

cm2/W

b  104 cm/W

Re c(3)  106 esu

Im c(3)  106 esu

c(3)  106 esu

0.04 0.06 0.10 0.12 0.15 0.06

2.92 3.57 3.78 3.81 3.89 3.11

0.23 0.38 0.65 0.75 0.95 0.36

2.93 3.59 3.84 3.89 4.01 3.13

S. Yuvaraj et al. / Optical Materials 73 (2017) 428e436 Table 3 Comparison of nonlinear absorption and optical limiting threshold with other similar materials. Sample

b (cm/W)

Optical limiting threshold (mW)

Ref.

NiFe2O4 CoFe2O4 MgFe2O4 ZnFe2O4 NiZnFe2O4 CuZnFe2O4 Mn0.40Cu0.60Fe2O4

1.35  1010 1.35  1010 6.14  103 5  1010 5.8  1010 7.9  1010 0.06  104

3.4 3.2 1.79 2.23 1.60 1.49 0.66

[49] [49] [21] [47] [47] [47] Present

[14]

[15]

[16]

[17]

[18]

4. Conclusion Co-precipitation route was used to synthesize the nano structured Cu doped Mn ferrite powders. Observation of few minor peaks of a-Fe2O3 impurity phase along with pure and Cu substituted Mn ferrites was confirmed by the XRD results. Single phase is obtained for the copper ferrites. Calculated lattice constant decreased while increasing the percentage of Cu2þ. The structural formation of cubic spinel ferrites was proved through the higher (590 cm1) and lower (448 cm1) frequency band as shown in the FTIR spectrum. From UV-Diffuse reflectance spectra, band gap values evaluated using Tauc relation are 1.83, 1.60, 1.52 and 1.51 eV respectively. HR-SEM picture shows the huge and unequal crystals which is found among the agglomerated nanoparticles. Quantitative analysis (EDX) confirms the existence of all the elements with the expected atomic ratio in the system of Mn1-xCuxFe2O4. In the PL spectrum, the improved NBE around the visible region established new novel promising materials for the multifunctional optoelectronic and photonic devices. Nonlinear characteristics and optical limiting studies show the materials to be potential candidates for optoelectronic device fabrication. References [1] Z. Abbas, M. Farooq, M. Azhar, I. Shakir, M. Shahid, M. Naeem, Impacts of neodymium on structural, spectral and dielectric properties of LiNi0.5Fe2O4 nanocrystalline ferrites fabricated via micro-emulsion technique, Phys. E Low Dimens. Syst. Nanostruct. 73 (2015) 169e174. [2] N. Singh, A. Agarwal, S. Sanghi, P. Singh, Synthesis, microstructure, dielectric and magnetic properties of Cu substituted NieLi ferrites, J. Magn. Magn. Mater. 323 (2011) 486e492. [3] S. Joshi, M. Kumar, S. Chhoker, G. Srivastava, M. Jewariya, V.N. Singh, Structural, magnetic, dielectric and optical properties of nickel ferrite nanoparticles synthesized by co-precipitation method, J. Mol. Struct. 1076 (2014) 55e62. [4] A.K.M. Akhter Hussain, M. Seki, T. Kawai, H. Tobata, Colossal magneto resistance in spinel type Zn1-xNixFe2O4, J. Appl. Phys. 96 (2) (2004) 1273e1275. [5] A. Elfalaky, S. Soliman, Theoretical investigation of MnFe2O4, J. Alloy. Compd. 580 (2013) 401e406. [6] K. Vamvakidis, M. Katsikini, D. Sakellari, E.C. Paloura, O. Kalogirou, C. Dendrinou Samara, Reducing the inversion degree of MnFe2O4 nanoparticles through synthesis to enhance magnetization: evaluation of their 1H NMR relaxation and heating efficiency, Dalton Trans. 43 (2014) 12754e12765. [7] F. Tabatabaie, M.H. Fathi, A. Saatchi, A. Ghasemi, Microwave absorption properties of Mn- and Ti-doped strontium hexaferrite, J. Alloys Compd. 470 (1e2) (2009) 332e335. [8] D. Chen, Y. Zhang, Z. Kang, A low temperature synthesis of MnFe2O4 nanocrystals by microwave-assisted ball-milling, Chem. Eng. J. 215 e 216 (2013) 235e239. [9] P.P. Goswami, H.A. Choudhury, S. Chakma, V.S. Moholkar, Sonochemical synthesis and characterization of manganese ferrite nanoparticles, Ind. Eng. Chem. Res. 52 (2013) 17848e17855. [10] X. Hou, J. Feng, X. Xu, M. Zhang, Synthesis and characterizations of spinel MnFe2O4 nanorod by seedehydrothermal route, J. Alloy. Compd. 491 (2010) 258e263. [11] U. Kurtan, R. Topkaya, A. Baykal, M.S. Toprak, Temperature dependent magnetic properties of CoFe2O4/CTAB nanocomposite synthesized by solegel auto-combustion technique, Ceram. Int. 39 (2013) 6551e6558. [12] D. Chen, H. Liu, L. Li, One-step synthesis of manganese ferrite nanoparticles by ultrasonic wave-assisted ball milling technology, Mater. Chem. Phys. 134 (2012) 921e924. [13] Y. Qu, S. Du, Y. Yang, Z. Ren, K. Pan, H. Fu, Synthesis, size and magnetic

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