Cadmium (C4H6MnO4.4H2O) salts had been blended and completely dissolved

Cadmium oxide with nanostructure has attracted anextensive attention due to the potential applications in chemical sensors and optoelectronicdevices 1-5. Although the highly toxicity of cadmium and its compounds, it isused in battery manufactures, corrosion protection in steels, and barriers tocontrol neutrons in nuclear fission processes.

CdO is n-type transparentconducting oxide(TCO) with a conductivity of 102–104 S/cmand good transparency especially in NIR spectral region with a direct band gapof nearly 2.2–2.7eV 1–3.

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Experimentally it was observed that one can controlthe optoelectronic properties of CdO by doping with different types of metallicions. So, doping with ions like Y,In,Sm,Cu 6–9 improves its n-type conduction. While doping with Cd2+ ions may enhance the low dimensional sizeto reach radius of 9.5×10-2 nm 10. CdO doped  with transition metals (3d elements)   or  magnetic  ions    such as Ni ,Mn, Co  and  Fe  11,12   could lead   magnetic properties  resulting  in dilute magnetic semiconductors (DMS). In general, doped semiconductors with 3d elements,known as dilute magnetic semiconductor (DMS), where a fraction of the magneticions substitute the host cations.

 The Ferromagneticbehavior of DMS materials made them useful in spintronic applications. Metalnanoparticles have attracted a great attention, resulting in novel opticl,magnetic and electronic properties. Calculationmethods based on density functional theory (DFT) also predict ferromagnetism inmost 3d transition metals (TM) based CdO 5–7. The structural defects andimpurities serves as traps or recombination centers for migrating chargecarriers generated by ionizing radiation. Electron Spin Resonance (ESR) can beused to evaluate such defects.

The aim of this study is to give more insightinto the effect of Mn on the structure, thermal and magnetic properties of CdO.2- Experimental  Procedure :DMS samples have been prepared using the co-precipitationmethod. The required amounts of cadmium nitrate Cd(No3)2.4H2O and Manganese Acetate (C4H6MnO4.4H2O)salts had been blended and completely dissolved in absolute ethanol.  Also a required amount of NaOH was completeddissolved in absolute ethanol. The two solutions were completely dissolvedusing a magnetic stirring for 1 hour at 60 oC. NaOH was added dropwise to the salts solution till complete precipitation.

The precipitate wasseparated by decantation process, washed with absolute ethanol and separated bycentrifuge with 5000 rpm for 15 minutes. The final ingot has been dried at 110 oCfor 1 hr and calcinied at 450 oC for 3 hrs. The dried powders weregrained in an agate mortar.     Shimadzu X-ray diffraction (XRD), with Cu(K?) tube, was used to determine the structure of  the as-prepared samples using. The range ofscanning angle ranging from 10 to 900.

The surface morphology of the investigated samples wereinvestigated using  Joel 6400 scanning electronmicroscope. Thermal analysiswas carried out using Shimadzu instrument (type-50), differential scanningcalorimeter (DSC-50) under nitrogen atmosphere (20 cm3 /min). Electronspin Resonance  (ESR) at room temperatureusing  Bruker   EMX spectrometer (X-band) German  were used to investigate the magneticproperties of the prepared samples. The magnetic hysteresis loops weredetermined using Lakeshore 7410  magnetometer (VSM) with the applied field   20 K Oe. 3-Resultsand Discussion:3-1-Structural Determination:Figure(1)  shows XRD of  the as- prepared Cd1-xMnxOPowder samples (x = 0.0,0.01, 0.05, 0.

1, 0.15, 0.2, and 0.3). All thediffraction peaks, which correspond to the planes (111), (200), (220),(311),(222) and (400), are perfectly indexed to the Cubic CdO structure (JCPDS65-2908), revealing that doping of Mn does not afect the structure of the CdO.The Diffract ograms reveal that there is no additional peak corresponding tosecondary phase of Mn in CdO, which confirms the formation of the Cd1-xMnxOsolid solution. Hence Mn2+ substitutes Cd2+ site into the crystal lattice.

Figure (1)illustrates that increasing Mn content leads to increase the  intensity  of diffraction peaks. This means the slightlydecrease of  the  nanocrystalline nature of the samples whichconfirmed by the crystallite sizes increasing as shown in table1. Table (1)shows the refined structural parameters obtained from Rietveld refinement usingthe PCW program. The obtained data reveal that the unit cell volume is almost acomposition independent. This is due to the small difference between ionicradius of Mn and Cd. The shifting of diffraction peaks towards lower angleswith the increase of Mn content suggested the incorporation of Mn+2 ions in CdO lattice at the site ofCd+2 ions 13. Figure (2) shows the refinement of CdO as anexample.

 The surface morphology, distribution of the particles and particle sizeof the undoped and doped samples were investigated by SEM. Figure (3) shows theSEM images of the investigated samples. The figure illustrates that theinvestigated samples  consists ofnumerous  irregular flowers like shapedstructure. The photomicrographs shows that addition of Mn did not change themain features of the growth process. 3-2-TransitionTemperatures and Crystallization Process: DSC thermograms for the investigatedcompounds measured at a constant heating rate of 10deg/min (Fig. 4) show thethree phenomena of  interest: the glasstransition (Tg ), The crystallization exothermic (Tc )and the melting endothermic (Tm ). The transition temperatures werelisted in table (2).

Theeffect of Mn doping on the kinetics of crystallization process of CdO wasstudied through determination of the kinetic parameters n (reflects thenucleation rate or the growth morphology) and the activation energy of theprocess. Avrami  phenomenological equation for solid-to-solidtransformation was used to describe the kinetics of isothermal crystallization14,15, a = 1- exp(Ktn)                         (1)Wherea  is the timedependent crystalline fraction at time t, n is Avrami exponent and K is thereaction rate,                                  K=K0(-E/kT)                                   (2)     Where T is the temperature in degreesKelvin, K0 is the rate constant and k is Bolzman constant. E is theapparent activation energy including the activation energy for nucleation Enand for growth EG and can be written as E= (En+ EGm )/n         (3)Where n and m are numerical factorsthat depend on the mechanism of crystallization mechanism n 3-dimension 2-dimension 1-dimension Surface nucleation 4 3 2 1 For prepared compositions containingnon-nuclei n=m+1, while n=m for compositions containing a large number ofnuclei.From equations ( 1&2 ) the followingequation could be derived:ln(-ln(1-a)) = ln K0 – E/kT + nlnt    (4) At constant (t ) plot of ln(-ln(1-?)vs. 1/T gives E.

Non-isothermal single scan techniquewas applied to determine the crystallization kinetic parameters of theinvestigated compositions. Slow constant scan-rate of 2 deg/min was used.  On this assumption a plot of log g(?) versus 1/Tyields a straight line when appropriate mathematical description of thereaction is used. Such a description can be written aslog g(?) = log (E Ko1/n / R) – E/nRT  (5)Kois considered constant with respect to temperature. The function  g() has been calculated by Savara and Stava16 for different reaction kinetic equations, details of the theoreticalapproach of the applied model are reported in a previous study 17 . The valueof E/n can obtained from the slope of the straight line from the plot of  g(a) vs. 1/T. Logg(a) versus 1/T was plotted for theinvestigated compositions for different kinetic equations.

The best fit for theincreasing part of DSC was obtained for the function A3 {A3= ?ln(1??)1/3= KT}. A3indicates the presence of random nuclei in the as-prepared  Cd1-xMnxO compositionsand that the growth of these nuclei is being diffusion controlled.  Figure (5) shows the plot of log g (?) versus 1/T for Cd1-xMnxO system forthe appropriate choice A3. From the figure, it can be noticed thatlogg(?) has two distinct slopes indicatingthat the crystallization process proceeds through two different rates. Fromthe slopes of the straight portions one can determine the values of theeffective activation energies E/n. The values of E were calculated from the slope of ln?ln(1 ??) versus 1/Tgiven in Figure (6). Table (3) gives the values of E and n.

The values of n reveal that the growth of the randomnuclei, formed in the as prepared samples, the crystallization process of CdOcan be carried out by surface nucleation while the doped compositionscrystallization takes place in two dimensions. The table illustrates thatadding 0.01 of   Mn to CdO leads todecrease the activation energy of crystallization from 34.24 to 23.

1 eV.  The table shows that the crystallizationenergy increasing with increasing Mn content which means that the addition ofMn impedes the crystallization process.  3-3-MagneticProperties:  Magnetizationversus magnetic field (M-H) hysteresis loop characterizes the magneticproperties of materials. Magnetization measurements on CdO and Mn doped CdOsamples were performed at room temperature in the range of applied magneticfield (0-2000G) as declared in figure (5). Figure (7) illustrates the presenceof magnetic order in the structure of the as-prepared samples. The figure showssmall loops passing through the origin for the investigated compositions. Theprepared Cd1-xMnxO nanostructures show a weakferromagnetic nature at room temperature, this may be due to the intrinsicdefect.

Metal doped CdO magnetic properties are mediated by the ferromagneticexchange between the available defect states in CdO and the dopant ion. Thedifferent magnetic parameters such as remnant magnetization (Mr), saturationmagnetization (Ms), reduced magnetization (Ms/Mr),coercivity (Hc) and hysteresis loop area are listed in table ( 4).It is obvious from this table that Ms decreases with increasing Mncontent upto 0.2.  The decrease of  Ms with increasing Mn content upto0.2 can be assigned  to the presence ofmagnetic disorder at the surface of the nanoparticles.  The relation between Mn concentration and Msis shown in figure (8).

The behavior of Mr with Mn concentration isthe same as that of Ms . Coercivity is an important parameter ofmagnetic materials, it reflects the degree of permanent magnetism. Table (4)shows that Cd0.80Mn0.2O  has the largest Coercivity value (885.

9 Oe ) this might open up possibleapplications in novel computer logic systems. The observed  ferromagnetic nature for the Mn-doped CdOfilm  may be due to the magneticinteractions between the dopant ions or might have originated fromsubstitutional spin polarized Mn atoms present in the host lattice. In metaloxide S.C., RTFM occurs due to the oxygen vacancies present in the lattice. Theincreased oxygen vacancies might also be responsible for the RTFM noted for theMn-doped CdO film.3-4-ESR Study:                                                                                                              ESR spectrum of theinvestigated samples are given in figure (9). The figure shows six splittinglines (hyperfine splitting) of undoped and doped CdO.

The hyperfine splittingis due to electron spin-nucleus spin interaction. Line width data can beextracted from any of the lines of the spectra. The chosen line at3200G becauseit has the highest amplitude. The calculated values of g and hyperfinesplitting constants are given in table(5). The electronic configuration of Mn2+ion is 3d5, and the electronic ground state is 6s5/2,which splits into three Kramers doublets (5/2, 3/2 and  1/2).Undpoed electrons ofMn2+ interact with neighboring Cd nuclei to give superfine lines.The hyperfine constant (A) is calculated by: A (cm-1)= (?B/ hc)*g* A (G)                    (6)Where (?B) is magneton Bohr (9.

27400949*10-24J.T-1), (hc) is Plank’s constant (6.6260693*10-34J.S)The g-value has been obtained using the following equation:                             g=h /BB0                                                 (7)where ?B is microwave frequency (9.45GHz)The obtained g of the investigated samples arearound 1.

9856. The g-factor depending on the electronic configuration of theradical or ion also represent spectroscopic splitting. Unpaired electron canlose or gain angular momentum, which may change the value of g-factor, causingit to differ from ge . This is significant to systems with metalions. As g-values show a negative shift with respect to the free electron value(2.0023),  the bonding is ionic in nature18.One  cancalculate the number of defects N from the following  relation:              N= K H0( H)2(A/2) /Ge?PHHm                           (8)Where K isconstant of spectrum (1013), H0 is the magnetic fieldcorresponding to zero point (3508.

797G), Hm is the width of the magnetic field from peak to peak (G), A is  the height of the signal (cm),Hm is modulation field (5), PH is Puissance (1.418)  and Geis gain detection (7960).The value of hyperfine constant (A), g- factor (g), the width of themagnetic field from peak to peak (? H), the height of the signal (A), andNumber of defects (N) are illustrated in table (5). From this table, it can be deduced that the width of the magneticfield from peak to peak increases with increasing the Mn concentration in Cd1-xMnxOsystem. The number of defects increases with increasing the Mn concentration,but the higher value of the number of defects in the  sample Mn5%.

4- ConclusionThe prepared nanostructure samples Cd1-xMnxO (x = 0.0,0.01, 0.05, 0.

1, 0.15, 0.2, and0.3 ) are having a cubic  structure andtheir  cell volume are almost composition-independent.

The absence of  Mn or Mn related impurity phases confirms theformation of Cd1-xMnxOsolid solution.  The non-isothermalkinetic analysis indicates that the crystallization of Cd1-xMnxOoccurs in two dimensional processes but ,that of CdO takes place through  surface nucleation process .ESR spectrum ofCd1-xMnxO showed Hyperfine lines.

Interpretation of theselines showed that Mn2+ ions occupy substitutional sites in cubicCdO.