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γ Effects of radiation and surfactant on Electrical and magnetic properties of cu0.1zn0.9mn2o4 nanoparticles

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https://www.eduzhai.net International Journal of M aterials and Chemistry 2012, 2(5): 197-204 DOI: 10.5923/j.ijmc.20120205.03 Influences of γ–Radiation and Surfactants on Electrical and Magnetic Properties of Cu0.1Zn0.9Mn2O4 Nanoparticles M. Khairy*, M. A. Mousa Chemistry Department, Faculty of Science, Benha University, Egypt Abstract Nanosized Cu0.1Zn0.9Mn2O4 were prepared by hydrothermal method in absence and presence of surfactants. The samples were characterized using XRD, SEM and TEM. A ll samp les showed spinel crystal structure with crystallite sizes depending on the preparation method and lay in the range of 17-89 n m. Electrical conductivity as a function of frequency and temperature has been studied. The conductivity results showed that all investigated samples behave like se miconductors and could be explained by hopping mechanism in which the conduction occurres via electron exchange amongst Mn+ and Mn+1 ions situated on octahedral sites in spinel lattice. Room temperature magnetic properties using VSM were studied. Effect of γ-radiation on the studied properties is investigated. Each of particle size, mo rphology, magnetic and electrical properties is affected with each of the type of surfactant used in the preparation method and γ- irradiat ion process. Keywords Nanosized Cu0.1Zn0.9Mn2O4, Surfactants, Gamma Irradiat ion, Electrical Properties, Magnetic Propert ies 1. Introduction Nanoparticles have been investigated intensively in recent years because of their size-dependent properties[1-5]. The synthesis of inorganic structures with nanoscale dimensions and mo rphological specificity is of a great importance and interest in material science and nanotechnology[1- 2]. After intensive research during the last decade, many techniques have been experimented for the control of shapes and morphologies of d ifferent nanomaterials[3, 4]. General approaches for shape control and production of anisotropic nanostructures rely on the availability of surfactants, which preferentially absorb on specific crystallographic faces. With ever increasing energy costs, the hydrothermal method could be possibly very attractive for fine powder preparat ion because of the low temperature involved and the good sinter ability of the formed powders[5, 6] . The electrical and structural properties of nanomaterials are strikingly different fro m those of their single crystalline, coarse-grained polycrystalline, and thin film counterparts. The d ielect ric constan t o f mat erials changes , when it t rans fo rms to nano ph ase fro m t h e b u lk fo rm. W h en compared with thin films, the value of d ielectric constant in nanostructured materials is very high[7]. The high surface to * Corresponding author: moh_khairy3@yahoo.com (M. Khairy) Published online at https://www.eduzhai.net Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved volume ratio of the gra ins, small size, enhanced contribution fro m grains and grain boundary regions, quantum confinement of charge carriers, band structure modification, and possibility for defects in grains are some of the factors which contribute to the electrical properties of nanostructured materials[7]. This d ifference between nano and bulk materials has immense theoretical and technological importance. Ionizing rad iation such as gamma ray has frequently been used in studies of the physical properties of crystalline solids[8]. Structural defects can be introduced by ionizing radiation. Severe d isruption of the lattice of a crystalline solid is possible, with the formation of a large number of d efects . Co mplex manganese oxides have recently evoked strong interest in various structures with diffe rent Mn valence states and Mn coordinations for examp le in perovskites or spinels. The manganites display a vast range of fascinating electrical and magnetic properties, which often co me about due to the mixed valence states of manganese. ZnMn2O4 is one of the promising materials which can be used as negative temperature coefficient (NTC) thermistors[9], as catalytic material[10] and as cathodic material of the secondary batteries[11] due to their excellent electrochemical properties. Doping materials can be used to induce and improve the properties of this material. As a part of our program to prepare nanomaterials of pure and substituted transition metal ZnMn2O4 and study their physical properties; this work was designed to prepare nanosized Cu0.1Zn0.9Mn2O4 by hydothermal method in 198 M . Khairy et al.: Influences of γ–Radiation and Surfactants on Electrical and M agnetic Properties of Cu0.1Zn0.9M n2O4 Nanoparticles absence and in presence of different surfactants. The materials obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrical properties (conductivity, dielectric constant and dielectric loss) as well as magnetic properties of the produced materials were studied. The effect of γ-irradiat ion on all the measured properties as well as the magnetic and electrical properties (conductivity, dielectric constant and dielectric loss) was also studied. 2. Experiments 2.1. Materials All the che mica l reagents used in the e xpe riment we re A.R. grade and used without further purificat ion and treatment. The surfactants used in the preparation method were divided into three different groups: (a) cationic surfactants: cetyl trimethyl ammon iu mbromide (CTAB){ CH3(CH2)15N(CH3)3Br } (98%) provided fro m Aldrich; (b) anionic surfactants: dodecylbenzene sulphonic acid (Su lph) {CH3(CH2)11C6H 4SO3H} provided fro m chemicals and dyes company, Kafr El Doar and (c) nonionic surfactants: triton X-100 (TX) {C14H22O(C2H4O)n} provided fro m Arsamco. of 2θ = 10-800. The density was determined by both the immersion Archimedes method and X- ray diffraction. Electron microscopes analysis using SEM and TEM were taken by an electron microscope model JEM-5200 Joel and Joel 2010, respectively. For electrical measurements, the powder samples were pressed uniaxially into a pellet of thickness 1–2 mm and of diameter 7 mm by applying pressure of ~ 0.3 Gpa for 3 min. Both faces of the pellets were coated with fine quality silver paint for good electrical contacts. Dc conductivity was measured in the temperature range 300-400 K by the four terminal technique. The temperature was limited to 400 K to prevent grain growth and to ensure that the main particle size remained the same in the entire temperature range. Ac conductivity was measured by the two-probe method using Fluke PM 6306 programmable auto matic (RCL) b ridge at frequencies fro m 102 – 106 Hz over the same temperature range used in dc-measurements. The hysteresis loop, saturation magnetization (Ms) and coercivity (Hc) of the materials under study were also measured by means of VSM at a maximu m applied field of 15 kG at roo m temperature. 3. Results and Discussion 3.1. Structural Characterizati on 2.2. Preparati on A mixed solution of 1 ml H2O2 (4%) and 8 ml NaOH (0.6 M) was poured slowly into a Teflon-lined stainless-steel autoclave filled with 4 ml Mn(NO3)2 (0.3 M ) and 5 ml surfactant (CTAB, TX or sulph) (5×10-3 M) while stirring vigorously, and the reaction solution was continually stirred and kept for 20 min. at the room temperature. 0.02mmol (3.28 g m) Mn(NO3)2, 9×10-3 mmo l (0.2.67g m) Zn(NO3)2·6H2O (GFS Chemicals), 1×10-3 mmo l ( 0.24 g m) Cu(NO3)2·3H2O (Merck) and surfactant (CTA B, TX or sulph) (5×10-3 M) were mixed in ~100 ml of distilled water to form Cu0.1Zn0.9Mn2O4. After that the reaction solutions were hydrothermally heated at 500 K for four days. The samples were cooled to roo m temperature, then the precip itates were filtered and washed with d istilled water several t imes until pH=7, and finally dried in an oven at 360 K. Half of the prepared samples was irradiated by γ-ray source using a 60Co gamma cell ( 60Co gamma cell 2000 Ci with a dose rate of 1.5 Gy/s (150 rad/s) at a temperature of 30 oC. Each sa mple was subjected to a total final dose of 1x105 Gy (10 Mrad). The prepared samples are denoted as Z, ZCTAB , ZTX, and Zsulph for the samples prepared without surfactant and by using CTAB, TX, and sulph surfactant, respectively. The irradiated sample is denoted by *. 2.3. Characterization X- ray d iffraction (XRD) were perfo rmed on the investigated samples using a Philips X’Pert Pro Super diffractometer with Cu Kα radiat ion (λ = 1.54 Å) in the range Intensity (A. u.) d c b a 10 20 30 40 50 60 70 80 2 θ (d2e0gree) Figure 1. XRD patterns for: a) ZCTAB b) ZTX c) Z d) Zsulph X-ray diffraction patterns of the investigated manganite samples are presented in Fig. 1. For all samples, the same patterns were observed with well developed (h k l) reflections, which can be well indexed on the basis of the tetragonal spinel structure with the space group of I41/amd JCPDS file (71-2499)[12]. No trace of impurity phases of starting materials is observed in the present patterns, indicating the high purity of the samp le. The spinel lattice of Cu0.1Zn0.9Mn2O4 consists of O2− anions form a close-packed tetragonal lattice in which the Zn2+ and Cu2+ cations are located in tetrahedral sites (labelled as A sites) and Mn3+ are located in octahedral sites (labelled as B sites), respectively; The samples exh ibit spinel International Journal of M aterials and Chemistry 2012, 2(5): 197-204 199 structure by a formula of Cu0.12+Zn0.92+[Mn3+]2O4. Where the ions inside the square bracket are located in octahedral sites and the ions outside the bracket are in the tetrahedral s ites [12]. The X-ray density of all the compositions was calculated using the formula: dXRD = Z/M/NV (1) Where Z/ is the number of molecu les per unit cell (Z/ = 4); M is the mo lecular weight; N is the Avogadro’s constant and V is the unit cell of the lattice. The bulk density (dA) was also measured by the Archimedes principle. The percentage porosity (P) of the samples was then calculated using the relation[13]: P = (1–dA/dXRD) x100 (2) The values of the bulk density and porosity were both tabulated in Table 1. Table 1. Density, grain size and porosity of investigated Cu0.1Zn0.9Mn2O4 samples interactions; the inorganic precursor and the cationic surfactant can form inorganic–surfactant composite templates. More analysis of SEM-micrographs showed also that the samples prepared using anionic surfactant (Zsulph) exhibit particles with d ifferent shapes aggregated with small and large grains sizes. This may be due to some kind of attraction forces between negative surfactant anions and the positive charges molecules of Cu, Zn, and Mn ions leading to agglomerate of part icles during the hydrothermal process. Generally, the different morphologies and sizes of crystallites formed during the hydrotherma l crystallization in presence of surfactants can be explained on the basis of the balance between nucleation and growth rates. With increase in each of the supersaturation and adsorption of surfactant on the crystal faces, both growth and nucleation rates increase. Consequently, when the growth rate dominates over the nucleation rate, crystallite sizes increase, while in the case of nucleation rate domination, crystallite size decreases[17]. Sample Vunit cell x1022 cm3 dXRD g/cm3 dA DTEM DXRD g/cm3 (nm) (nm) P% d Z*sulph 2.977 5.333 3.895 [24] [22] 27.0 Z sulph Z* 2.991 2.988 5.309 3.751 18 17 29.4 5.314 3.995 [45] [42] 24.9 Z 2.991 5.309 3.895 37 38 26.6 Z * Tx 2.991 5.308 4.083 [71] [74] 23.1 c ZTx 2.994 5.303 3.995 65 67 24.7 Z*CTAB 2.991 5.309 4.132 [88] [89] 22.2 ZCTAB 2.994 5.303 4.091 81 84 22.9 h 1 µm g 1 µm X-ray diffraction line broadening based on (311) peak was used to estimate the crystallites size (DXRD) of the powder by using Scherrer formu la[14]: DXRD = 0.9 λ/ β cos θ (3) Here λ is the wavelength of the Cu Kα radiation (λ = 1.5406 Å), β is the full width half maximu m (FW HM) in radians calculated using Gaussian fitting. In our experiment, β was corrected by this formu la β=βm−βS (4) Where βm is the measured FWHM of the sample studied, βS the FWHM of silica, which was used to avoid the broadening from the X-ray instrument. The estimated crystallites sizes of all the samples under investigation are presented in Table 1. Fig. 2 shows the surface micrographs of the irradiated and unirradiated samples. The SEM-image analysis reveals the role of surfactants as a capping agent. The mo rphology of the samples prepared in absence of surfactant (Z) showed a range of shapes including deformed polyhedral and spherical shapes. Whereas the sample prepared using triton surfactant (ZTX) showed large grains with spherical shapes. On the other hand, the samples prepared using CTAB surfactant (ZCTAB) showed the formation of nano rods particles. It was reported that CTA B has been successfully used as the morphology-direct ing agent for the synthesis of one-dimensional nanostructures, such as CuO, PbO2, Pb3O4 and Co3O4 nanorods[15, 16]. In this synthesis, CTAB can be worked as a capping agent or making some the electrostatic 1 µm b f 1 µm 1 µm a e 1 µm 1 1 µm Fi gure 2. SEM: a) ZCTAB b) ZTX c) Z d) Zsulph e) Z*CTAB f) Z*TX g) Z* h) Z*sulph SEM micrographs of irrad iated samples showed a surface morphology and voids between the particles grains differs to some extent than that of unirradiated ones. And in the same time, the pores sizes became to some extent larger after irradiation process. This refers to that the high ionization radiation creats some defects diffusing in the crystals to produce some effects on the surface of the sample. The nano rods particles showed in ZCTAB samples have average length of 80 n m and diameter of 40 n m accord ing to TEM image Fig. 3. Generally, the mean particle sizes DTEM of all samp les investigated lie between 17 -89 n m, Table (1), which is smaller than DXRD. Th is may be attributed to either the presence of non-crystalline materials at the lattice surface or to the different approach of two techniques. In XRD, the 200 M . Khairy et al.: Influences of γ–Radiation and Surfactants on Electrical and M agnetic Properties of Cu0.1Zn0.9M n2O4 Nanoparticles crystals are randomly distributed; the estimated crystal size fro m XRD was the average size of the length, and the accuracy of the Scherre`s equation is affected by many factors such as diffraction line width, defects, surface tension , so the Scherrer formu la may induce some errors in measuring the absolute values of the crystallite size. The size of voids in irrad iated samples is smaller than that of unirradiated ones. This may be attributed to the creation of some defects produced by ionizing radiation. plots the activation energy values Edc have been calculated and listed in Table 2. It is evident to see that the conductivity increases with increasing the crystallite size. This is due to the fact that samples with s mall grains contain more number of grain boundaries than grains. The grain boundaries are the regions of mis match between the energy states of adjacent grains and hence act as barriers to the flow of electrons causing a decrease in conductivity with decreasing particle s ize. d h c g lnσdc (ohm-1. Cm-1) b f a e Figure 3. TEM: a) Zsulph b) Z c) ZTX d)ZCTAB e) Z*sulph f ) Z* g) Z*TX h) Z*CTAB 3.2. Electrical Properties 3.2.1. Dc Conductivity The electrical properties of transition metal o xides with spinel structure depend on several factors, including the method of synthesis, grain size and chemical co mposition. The dc-conductivity (σdc) of the samples investigated is evaluated using the relation: σdc = l/ RdcA (5) where Rdc is the dc resistance, l is the thickness, and A is the area of the electrode deposited on the sample. The temperature dependence of dc-conductivity for all γ-irradiated and unirrad iated samples showed the same behavior, Fig. 4. The figure shows that the electrical conduction in the material is a thermally activated process and it can be explained in accordance with the relation: σdc = σo e xp (-Edc/kT) (6) Where σo is the pre -e xponential factor, Edc is the activation energy k is the Bolt zmann constant. Fro m the slopes of the Figure 4. T he temperature dependence of DC-conductivity for:(♦), ZSulph; (■), Z; (▲), ZTX; (●), ZCTAB In other words, it can be said that the variation in electrical properties with the particle size is mainly attributed to the spatial confinement of free and bound charges, and disorder grain boundary. It had been reported that the grain boundaries in nanocrystalline materials exh ibit a random atomic arrangement without short or long range order[18]. However, the obtained results refer to that the nature and volume fraction of the gra in boundaries are very important in determining the electrical properties of consolidated n an o p articles . The electrical conductivity values obtained in our Cu0.1Zn0.9Mn2O4 samples are higher than that obtained for nano-ZnMn2O4 (5.3x10-7 oh m-1 cm-1)[19]. This refers to that the addition of Cu+2 causes a change in the valence states of Mn-ions present in the investigated samples and hence in their conductivity value. Gamma irrad iated process produces an increase in the conductivity values without a change in the activation energies, Table 2. Th is may be attributed to the following interaction: γ + Mn3+ → Mn3+n + e (5) This interaction leads to a change in the arrangement of cations in both tetrahedral and octahedral sites of the spinel lattice. The ionization of Mn3+ to Mn3+n (o xidation states higher than 3+ i.e. Mn4+ or Mn5+…etc.) by irradiation causes a creation of an equivalent proportion of Mn2+ on the same sites, in order to maintain the electrical neutrality. Th is leads to the formation of Cu2 +0.1Zn2 + 0 .9[Mn3+2-2xMn2+x Mn4+x] O42-. International Journal of M aterials and Chemistry 2012, 2(5): 197-204 201 The formation of this cation distribution causes an increase in the hopping rate of electrons between the diffe rent valence states of Mn-ions and hence an increase in the conductivity. It should be mentioned here that the distances between the ions present on octahedral sites are s maller than that present between the tetrahedral sites, which lead to increase the effective contribution of the octahedral ions in the conduction process. Table 2. Conductivity data of γ-irradiated and unirradiated Cu0.1Zn0.9Mn2O4 samples at 300 K Sample Z*sulph Zsulph Z* Z Z*TX ZTX Z*CTAB ZCTAB DTEM (nm) [24] 18 [45] 37 [71] 65 [88] 81 σdcohm-1.cm-1) [1.4x10-6] 6.8x10-7 [8.64x10-6] 2.35x10-6 [1.96x10-5] 7.28x10-6 [6.32x10-5] 1.63x10-5 Ed c (eV) [1.34] 1.53 [1.22] 1.44 [1.15] 1.29 [1.07] 1.19 [ ] irradiated data 3.2.2. AC-conductivity In order to give informat ion on the type of polarizat ion present in the samples, the ac-electrical conductivity (σac), at temperatures range of 300-400 K and at frequency range of 102 – 106 Hz were studied. The ac-conductivity σac (ω) was calculated according to σac (ω) = σt (ω ) - σdc (7) Where σt (ω) is the measured total frequency-dependent conductivity. 1.6E1-0.63 1.21E-.023 8.0E0-0.84 Z Z(slph) Z(TX) ZCTAB ZCTAB ZCTAB ZCTAB lnσAc x 103 (osihgmm-1a.ACCm-1) 4.0E0-0.44 0.0E+000 0.000E+00 2.002E+06 ω x 104-6.0(04HE+z0)6 w 6.006E+06 Figure 5. The frequency dependence of AC-conductivity for: (■); Z(Sulph), (♦);Z, (▲); ZTX, (x); ZCTAB(300K), ( X ); ZCTAB(340K), (●); ZCTAB(380K), (+); ZCTAB(400K) Fig. 5 shows the frequency dependence of σac at 300 K for unirradiated samples. The same variation is also observed for irradiated samples with different particle sizes. All the samples show an increasing trend in the ac - conductivity as the frequency increases. However, as the frequency increases the conductivity becomes more and more frequency dependent. The origin of frequency dependence of conductivity in the relaxation phenomenon arises due to mobile charge carriers[20]. In a hopping model, it is possible to distinguish different characteristic regions of frequency. In our case, at low frequencies the conductivity is low due to grain boundary effect wh ich acts as hindrance fo r mob ility of the charge carriers. The hopping mechanism becomes the sole contribution to the conductivity process in the frequency regions where the conductivity is strongly dependent on freq u en cies . 3.2.3. Dielectric Behavior The frequency dependence of dielectric constant ε`and dielectric loss ε`` of nanosized Cu0.1Zn0.9Mn2O4 at different temperatures is studied. A similar trend is observed for all irradiated and unirradiated samples, some typical plots are shown in Fig 6 and Fig. 7. It shows dielectric dispersion where both real and imag inary dielectric constant decreases rapidly with increasing frequency in low-frequency region while it approaches almost frequency independent behaviour in high frequency region. The decrease in imaginary part of dielectric constant is pronounced more in co mparison to real dielectric constant. The dielectric d ispersion curve can be explained on the basis of Koop's theory[21] based on the Maxwell–Wagner model fo r the in-ho mogeneous double structure[22]. According to this model the dielectric structure was supposed to be composed of the double layer. The first layer is of fairly well conducting materia ls, which is separated by the second thin layer (grain boundaries) of relatively poor conducting substance. The grain boundaries were found to be more effective at lo wer frequencies while the magnetite g rains are more effective at higher frequencies. In present samples, Cu0.1Zn0.9Mn2O4 are dipolar materials due to the presence of majority Mn3+ ions and minority divalent ions in them. The electron exchange between trivalent and divalent ions gives local displacement of electrons in the direction of applied electric field thus inducing polarization in manganite. The decrease in the complex permitt ivity with increasing frequency is exp lained to be due to the decrease of polarization of the dipoles when electric field propagates with h igh frequency. In other words, in d ielectric nanostructured samples, interfaces with large volume fractions contain a large number of defects, such as dangling bonds, vacancies, vacancy clusters, and micro porosities, which can cause a change of positive and negative space charge distribution in interfaces. When subjected to an electric field, these space charges move. When they are trapped by defects, a lot of dipole mo ments are fo rmed. At low frequency region these dipole mo ments are easy to follow the change of the electric field[23]. So the dielectric loss and hence the dielectric constant shows a large value at low frequency. For all investigated samples, the dielectric constant ε` was found to increase with increasing the particle size. Th is can be explained on the basis of many factors, such as amorphousness of surface, high surface energy, micro mechanical stress, surface domain depolarisation, domain wall e ffects, and so on. 202 M . Khairy et al.: Influences of γ–Radiation and Surfactants on Electrical and M agnetic Properties of Cu0.1Zn0.9M n2O4 Nanoparticles 8000 Z(CTAB) 6000 4000 Z(TX0 Z Z(sulph) Z(CTAB) M (emu/g) 2000 E` 0 1 3 5 7 log f (lHogzf) Figure 6. The frequency dependence of dielectric constant of: (●), ZSulph; (▲), Z; (■), ZTX; ( ♦), ZCTAB(300K); ( X ), ZCTAB(400K) 6000 4000 Z(CTAB) Z(TX0 Z Z(sulph) Z(CTAB) E`` ` ` 2000 0 1 3 5 7 log flo(gHfz) Figure 7. The frequency dependence of dielectric loss of : (●), ZSulph; (▲), Z; (■), ZTX; ( ♦), ZCTAB(300K), ( X ), ZCTAB(400K). The results obtained showed also that each of the dielectric constant and the dielectric loss increases with an increase of temperature. This is expected because as the temperature increases, the resistivity of the samples decreases and polarization increases. With the increase in temperature the thermal act ivation enhances the number of dipoles available for polarizat ion. 3.3. Magnetic Properties Vibrat ing sample magnetometer (VSM) was used to investigate the magnetic properties of γ-irradiated and unirradiated Cu0.1Zn0.9Mn2O4 at room temperature. A ll samples showed narrow hysteresis loops, indicating their slight ferro magnetism. Typical plot is shown in Fig. 8. The irradiated ones showed the same behavior. The saturation magnetizations Ms of the samples were found by extrapolating M vs. 1/H plot to 1/H=0. The variat ion trend of Ms, Hc and Mr was illustrated in Table 3. Fro m wh ich it can be seen that magnetization (Ms) values for irradiated are higher than unirradiated ones and increase in the following order: ZCTAB > ZTX > Z > Zsulph field kG Figure 8. Room temperature magnetic hysteresis loop of Z sample The ferro magnetic properties of studied samples were attributed to the simultaneous presence of Mn4+ and Mn3+ and Mn2+ ions. They give rise to ferromagnetism via the double-exchange mechanis m. Zn and Cu -ions acting as the retardant of the magnetic interaction between the manganese ions. The increase in ferro magnetic character of the samples by irradiation, Table 3, may be attributed to the increase occurring in the ratio of o xidizing and reducing amount of Mn – ions such as Mn3+/ Mn4+ comparable with that present in unirradiated ones, as mentioned above. In summary, the different ferro magnetic properties values of different samples may be attributed to the different Mn3+/Mn4+ co mp o s itio n s . Table 3. Magnetic Properties parameters of Cu0.1Zn0.9Mn2O4 Sample Z*sulph Zsulph Z* Z Z*TX ZTX DTEM (nm) 24 18 45 37 71 65 Ms (emu/g) [0.20] 0.29 [0.42] 0.52 [0.78] 0.95 Hc (G) [72] 88 [90] 102 [106] 122 Mr (emu/g) [0.008] 0.010 [0.011] 0.013 [0.013] 0.015 The nanorod sample ZCTAB exhibit saturation magnetization (Ms) value, which is higher than that of other samples. This increase in magnetic propert ies may be strongly dependent on the growth direction of[110] wh ich is one of the easiest magnetization in the spinel system[24]. Similar results were also found with Fe2O3 nanowires[25]. The increase observed in saturation magnetization with the increase in particle size, Table 3, is attributed to the nature of ultrafine particles, including the surface disorder and surface spin canting due to large surface to volume rat io for nanoparticular system[26, 27]. This may be also attributed to different mechanisms, such as the existence of a magnetically dead layer on the particles surface, the existence of canted spin or the existence of a spin glass like behavior of the surface spins[24-28]. 4. Conclusions International Journal of M aterials and Chemistry 2012, 2(5): 197-204 203 Nanocrystalline Cu0.1Zn0.9Mn2O4 were prepared in the range of 18-85 n m using hydrothermal method in presence and absence of surfactants. XRD showed a tetragonal spinel structure for the γ- irrad iated and unirradiated samples. The size of the prepared particles has been confirmed through X-ray diffract ion and TEM techniques. SEM and TEM images showed surface and particle mo rphology depends on each of the type of surfactants used and irradiation process. The pores sizes became also smaller after γ-irradiation process. Both ac- and dc-conductivity follows Arrhenius-type thermally activated conduction over temperature range investigated and referring to a semiconducting behavior for the γ-irradiated and unirradiated nano Cu0.1Zn0.Mn2O4 samples. The irradiation process causes an increase in the conductivity values. Hopping mechanism between different o xidation states of Mn-ions in Cu 2+ 0.1 Zn2+0.9[Mn3+ 2-2x Mn2+xMn4+x] O4 2 -s amp les is used to explain the conducting behavior. The dielectric constant (ε′) and d ielectric loss factor (ε′′) decreases exponentially with increasing the measured frequencies and increases with increasing temperature at each indiv idual frequency due to the relaxat ion of the dipole molecules. All studied samples showed ferromagnetic behavior which increases with increasing each of the particle size and irradiation process. The relation between mo rphology (nano rod) and magnetic performance is observed. irradiated with gamma- rays, J. Radioanaly. Nucl. Chem. 273 (2007) 609-614. [9] S. Guillemet-Fritsch, C. Chanel, J. Sarrias, S. Bayonne, A. Rousset, X. Alcobe, M . L. M artinez Sarriòn, Structure, thermal stability and electrical properties of zinc manganites, Solid State Ionics, 128 (1-4) (2000) 233-242. [10] G. Ferraris, G. Fierro, M . Lo Jacono, M . Inversi, R. Dragone, A study of the catalytic activity of cobalt–zinc manganites for the reduction of NO by hydrocarbons, Appl. Catal. B 36 ( 4) ( 2002) 251-260. [11] F. Liu, R. Kirchheim, Nano-scale grain growth inhibited by reducing grain boundary energy through solute segregation, J. Cryst. Growth, 264( 1-3) (2004) 385-391. [12] A.C.F.M . Costa, A.M .D. Leite, H.S. Ferreira, R.H.G.A. Kiminami, S. Cava, L. Gama, Brown pigment of the nanopowder spinel ferrite prepared by combustion reaction, J. Eur. Ceram. Soc. 28 (2008) 2033–2037. [13] A. Karamanov, M . Pelino, Induced crystallization porosity and properties of sintereds diopside and wollastonite glass-ceramic, J. Eur. Ceram. Soc., 28 (3) ( 2008) 555-562. [14] H.P. Klug, L.E. Alexander, X-ray diffraction procedures for polycrystalline and amorphous materials, Wiley, New York (1970). [15] S. Lian, E. Wang, Lei Gao, Lin Xu, Fabrication of single-crystalline Co3O4 nanorods via a low-temperature solvothermal process, M ater. Lett., 61 (18) (2007) 3893-3896. REFERENCES [16] M . Cao, C. Hu, Y. Wang, Y. Guo, C. Guo and E.B. Wang, Chem. Commun. 1884 (2003). [1] T. M ousavand, S. Ohara, M . Umetsu, J. Zhang, S. Takami, T. [17] L. Carbone, P. D. Cozzoli, Colloidal heterostructured Naka, T. Adschiri, Hydrothermal synthesis and in-situ surface nanocrystals: Synthesis and growth mechanisms, Nano modification of boehmite nanoparticles in supercritical water. J. Supercrit. Fluids 40 (3) (2007)397-404. Today, 5 (5) (2010) 449-493. [18] V. Biju, M . Abdul Khadar, Analysis of AC electrical [2] D.G. Shchukin, G.B. Sukhorukov Nanoparticle Synthesis properties of nanocrystalline nickel oxide, M ater. Sci. . Eng.: in Engineered Organic Nanoscale Reactors, Adv. M ater. A 304–306 (2001) 814–817. 16 (8) (2004) 671–682. [19] M . Khairy, M . A. M ousa, Synthesis, characterization, [3] J. Oh, J. Lee, S. J. Kim, S.B. Han, K. Park, TiO2 Branched catalytic and electrical conductivity of nanosized gamma Nanostructure Electrodes Synthesized by Seeding M ethod for Dye-Sensitized Solar Cells, Chem.Mater., 22 (3)(2010) irradiated and unirradiated ZnM n2O4, in press. 1114–1118. [20] B. Treev, “Physics of dielectric materials”, 1988, M ir. [4] T. Nomura, T. Mori, H. Arima, Y. Konishi, Shape and size M oscow. control of barium chromate nanoparticles using reverse [21] C.G. Koops, On the Dispersion of Resistivity and Dielectric micelle, Adv. Powder Technol., 20 ( 1) (2009)101-105. Constant of Some Semiconductors at Audio frequencies, [5] Y. Li, Y. Guo, R. Tan, P. Cui, Y. Li, W. Song, Synthesis of Phys. Rev., 83 (1951) 121 -124. SnO2 nano-sheets by a template-free hydrothermal method, [22] T. Hanai and K. Sekine Theory of dielectric relaxations due to M ater. Lett., (63)( 24-25) (2009) 2085-2088. the interfacial polarization for two-component suspensions of [6] X. Shi, Y. Xiao, L. Yuan, J. Sun, Hydrothermal synthesis and spheres, Colloid & polymer Sci.64 (1986) 888-895 . characterizations of 2D and 3D 4ZnO·B2O3·H2O [23] N W Grimes, Dielectric constants and the oxide additivity nano/microstructures with different morphologies, Powd. rule-comments on a recentinvestigation of M gAl2O4 spinel, J. Technol., 189(3) (2009) 462-465 Phys.: Condens. M atter 4 (1992 ) L567. [7] S. Kurien, J. M athew, S. Sebastian, S.N. Potty, K.C. George, [24] Z. Jiang, J. Han and X. Liu, Study on Structure and Dielectric behavior and ac electrical conductivity of M agnetization of Spinel Ferrites, Adv. M ater. Res. (152 - 153) nanocrystalline nickel aluminate M ater. Chem. Phys., 98 (2-3) (2010) 274-278. (2006) 470-476. [25] R.K. Gupta, K. Ghosh, L. Dong, P.K. Kahol, Structural and [8] T. Tuner, M. Ko rkmaz, ESR study of ascorbic acid magnetic properties of phase controlled iron oxide rods, 204 M . Khairy et al.: Influences of γ–Radiation and Surfactants on Electrical and M agnetic Properties of Cu0.1Zn0.9M n2O4 Nanoparticles M ater. Lett., 65(2)(2011)225-228. M agn. M agn. M ater., 200, (1-3)(1999)359-372. [26] A. Ceylan, S. Ozcan, C. Ni, S. I. Shah, Solid state reaction synthesis of NiFe2O4 nanoparticles, J. M agn. M agn. M ater. 320 (2008) 857-863. [27] R.H. Kodama, M agnetic nanoparticles - Condens. M atter, J. [28] J. Chandradass, M . Balasubramanian, Ki Hyeon Kim, Size effect on the magnetic property of CoAl2O4 nanopowders prepared byreverse micelle processing, J. Alloys Compd. 506 (2010) 395–399.

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