International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015 1688

ISSN 2229-5518

Structural and Dielectric Studies of Gadolinium

Substituted Nickel Ferrite Nanoparticles

Rafeekali K, Muhammed Maheem, E.M. Mohammed
Research department of physics, Maharajas college, Eranakulam, Kerala

Abstract— Nanoparticles NiFe2-xGdxO4 (x=0, 0.1, 0.2, 0.3, 0.4) ferrite was prepared by solgel combution method. The samples were characterized with X-ray diffraction and SEM measurements. The effect of Gd3+ cations substitution on structure of prepared nanoparticles was investigated. From the analysis, the system was found to be inverse spinel cubic structure. The lattice parameter (a) increases with Gd doping content. . Room temperature DC electrical resistivity decreases .Dielectric properties have been studied in the frequency range of 1 kHz to 5 MHz. Permittivity and tangent loss (tanδ) decreases with the substitution of Gd3+ in parent crystal structure.

Keywords: Rare earth ions, XRD, Dielectric properties, Permittivity.

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1 INTRODUCTION

n the recent years, so much attention has been paid to the nano- magnetic materials that show very interesting magnetic properti es. In this material, different properties and applications are appeared
as compared to their bulk counterparts. The magnetic properti es of nanomaterials are used in medical, electronic, and recording indus- tries that depend on the size, shape, purity and magnetic stability of these materials. In biomedical application, one can use nano magnet- ic materials as drug carriers inside body where the conventional drug may not work. For this purpose, the nanosize particles should be in the super paramagnetic form with a low blocking temperature. Fer- rite nanomaterials are obj ect of intense research because of their proper magneti c properti es. It has been reported that when the si ze of particles reduced to small size or in range of nanomaterials, some of their fundamental properti es are affected. nano ferrites are simulta- neousl y good magnetic and dielectri c materials. These properti es of the nano ferrites are affected by the preparation conditi ons, chemical composition, sintering temperature and the method of preparation . Several chemical and physical methods such as spray pyrol ysis, sol- gel, co-precipitation, combustion technique, high energy milling etc. have been used for the fabricati on of stoichi ometri c and chemicall y pure nano ferrite materials. Among the available chemical methods, the sol-gel technique is an excell ent method to synthesize rare earth substituted nanoparticles with maximum purity. In spite of the devel- opment of a vari ety of synthesis routes, the producti on of ni ckel fer- rite nanoparticles with desirable size and magnetic properties is still a challenge. This would justify any effort to produce size tuned nick- el ferrite nanoparticles with rare earth substitution.In the present paper, the structural and magnetic properti es of gadolinium substitut- ed nickel ferrite and XRD,SEM and DIelectri cal properti es were investigated.

2. Experimental

2.1. Synthesis

Nano particles of Gadolinium substituted nickel ferrite were synthe- sized by the sol-gel combustion method. A stoichiometric ratio of NiFe2-x Gdx O4 (x=0, 0.1, 0.2, 0.3, 0.4) were dissolved in ethylene
gl ycol using a magnetic stirrer. The fi ve sample solutions was then heated at 60 °C for 2 hours until a wet gel of the metal nitrates was obtained. The gel was then dried at 120 ° C. This resulted in the self ignition of the gel producing a highl y voluminous and fluff y product. The combustion can be considered as a thermally induced redox reacti on of the gel wherein ethyl ene gl ycol acts as the reducing agent and the nitrate ion acts as an oxidant. The nitrate i on provides an oxidizing envi ronment for the decompositi on of the organic compo- nent. The obtained powder of di fferent samples NiFe2-x Gdx O4 (x=0,
0.1, 0.2, 0.3, 0.4) was ground well collected in di fferent packets for
the measurements.

2.2. Characterization

The gadolinium doped nickel ferrite samples were characteri zed by an X-ray powder di ffract meter (XRD, Bruker AXS D8 Advance) using radiation (wavelength= 1.5406 A° ) at 40 kV and 35 mA. Lat- tice parameter was calculated. The crystal structure, crystallite size and X-ray density were determined. The particl e size was determined using scanning electron microscopy(TESCAN VEGA3SBH). Elec- trical studies conducted using RF material analyser(AGI LENT E4991A)

3. Results and Discussion

3.1. Structural Analysis

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International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015 1689

ISSN 2229-5518

Fig.1. XRD patterns of NiFe2-x Gdx O4 (x=0, 0.1, 0.2, 0.3, 0.4)

The XRD patterns of NiFe2-x Gdx O4 (x=0, 0.1, 0.2, 0.3, 0.4) nano- particles are depicted in Fig. 2 and are typical of spinel structure. Comparing the XRD pattern with the standard data, the sample with gadolinium concentrati on zero shows highest peak and concentration
0.4 shows lowest.The di ffracti on peaks are broad because of the na- nometer size of the crystallite. The crystallite size ‘ D’ of the samples has been estimated from the broadening of XRD peaks using the Scherrer equation.Lattice parameter ‘ a’ for all the samples has been calculated by interplanar spacing (dhkl) and 2-theta values using the standard relation,Value of lattice constant for x=0.0 comes out to nbe
8.3865Å, well in agreement with reported value. Lattice constant has increased monotonicall ywith increment in Gd3+ concentration. This increase can be easil y explained due to substitution of large ionic radii of Gd3+ (0.94Å) in place of smaller Fe3+ (0.67 Å) ions. Also rare earth ions are usuall y present at grain boundaries that cause hin- drance in the grain growth, therefore crystal size and unit cell param- eters increases.
The crystallite size was observed to increase with the increase of gadolinium concentration. It has been reported that the doping pro- cess generall y decreases lattice defects and strain, but this technique can cause the coalescence of smaller grains, resulting in an increased average grain size for the nanoparticles . Calculated values of l attice parameter of gadolinium substituted nickel ferrite samples were in close agreement with standard data.

3.2. SEM Analysis

Fig.2. SEM Image of NiFe2-x Gdx O4 at x= (0.00, 0.1)

graph has been taken from the samples which were doped with gado- linium concentrati on 0.0 and 0.1. Particle size is obtained around
23.0 nm with mono disperesed nano particles as one can see from the photograph. It Shows the surface morphol ogy and grain size for the prepared sample x=0.0 and x=0.1. It is clear from the image that uni- forml y distributed; less agglomerated and homogenous spherical particles have been formed in a controlled environment by sol-gel combustion technique. Micrographs also confirm the increase in grain size with Gd3+ doping in the parent crystal structure. The ho- mogeneity of shape and grain size largely affects the electri cal and magnetic properti es of ferrites.

3.3. Dielectric study

Dielectri c behavi or of nano spinel ferrites mainly depends upon the nature and distribution of metal cati ons on A-sites and B-sites in the spinel lattice. Spinel nickel ferrites are considered good diel ectri c materials and the high frequency di electri c behavior is mainly de- pendent upon the particle size and method of synthesis of nano parti- cles. Different studies have been provided relating the dielectricpa- rameters of Gd3+ doped ferrites. Dielectri c parameters (real and imaginary parts of relative permittivity, diel ectri c loss tangent) for the prepared seri es of NiGdx Fe2-x O4 (x=0.0 to x=0.4) havebeen stud- ied in the frequency range 1 MHz to 1GHz at room temperature. Figs.3 shows the variation of relati ve permittivity with frequency at room temperature. It can beobserved from the figure that rel ative permittivity for all the samples decreases with increase in frequency and ultimately becomes constant at higher frequenci es. This decrease in permittivity is more rapid in the low frequency region and be- comes sluggish as the applied frequency increases. This behaviour is subjected to diel ectric polarization under the application of AC field.

Fig.3. Variation of permittivity as a function of frequency

It can be seen that dielectri c l oss tangent has the same trend as per- mittivity l osses. It decreases with increase in frequency and becomes constant up to 1GHz due to decreased polarizati on at high AC fields. At x=0.4 shows a low loss dielectri c behavi our which allows its use in high frequency data reading/writing in electroni c structures
The SEM system that has been used for morphol ogy of sample was
CAMSCAN MV2300 model with 15 KV applied voltage. Photo-

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t x=0.4 shows a low loss dielectri c behaviour which allows its use high frequency data reading/writing in electroni c structures.

Fig.4. Variation of dielectric loss as a function of frequency

4. Conclusions

Nano spinel NiFe2-x Gdx O4 with x in step increment has been syn- thesized by sol-gel Combustion method. All the studied samples are pure cubic spinel phase ferrites without any impurity metal oxides. Lattice constant and crystallite size increases with increase in Gd3+ concentrati on, due to increase i onic radii and atomic weight of gado- linium as compared to Fe3+. Substitution of Gd3+ i on in parent crys- tal causes a lattice distortion that can be observed by increased lattice strain in W-H plots. Dielectri c constant and loss tangent decreases to
4.92 and 0.016 respectivel y with increase in the dopant concentration showing that the material with x=0.4 is a low loss dielectri c.

5. Acknowledgements

RK and MM acknowledges the Maharajas College under Mahathma Gandhi Universty for providing LAB faciliti es. EMM thanks DST and UGC for the financial support. Authors thank SAIF,CUSAT Ko- chi, SAIF, II T Madras and SAIF IIT Mumbai for providing XRD, FTIR, VSM and TEM measurement facilities.

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