Magnetic and electrical properties of calcium doped Cobalt spinel ferrites (Co 1-x Ca x Fe 2 O 4 ) synthesized by solution combustion method

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1 International Journal of Dynamics of Fluids. ISSN Volume 13, Number 2 (2017), pp Research India Publications Magnetic and electrical properties of calcium doped Cobalt spinel ferrites (Co 1-x Ca x Fe 2 O 4 ) synthesized by solution combustion method Anu Department of Chemistry, BUC College, Batala (Gurdaspur), Punjab , India. buccanu@gmail.com Abstract Solution combustion method has been used for synthesis of pure and calcium doped cobalt spinel oxides (Co1-xCaxFe2O4 : x = ) using urea as a fuel and oxidizer. Powder X-ray diffraction analysis (XRD) indicates pure and crystalline nature of ferrites. Vibratory sample magnetometric (VSM) study of the synthesized ferrites reveals their magnetic nature which increases with the concentration of Ca 2+ dopant. Electrical properties of the doped samples carried out by two probe method show increase in the conductivity values. These ferrites synthesized have unique electro-magnetic properties and can be used as magnetic cores in computer, hard discs etc. Keywords- crystalline, magnetic nature, electro-magnetic, magnetic devices 1. INTRODUCTION With the recent advances in scientific and technological fields, soft magnetic materials have been in a extreme demand because of their probable applications in areas like drug delivery, data-storage, ferrofluid and sensing devices technology. Among these, spinel ferrites with the general formula MFe2O4, are usually studied because of their assorted electrical and magnetic properties which mainly originate from their structural properties along with the ion distribution over octahedral and tetrahedral sub-lattices [1].

2 232 Anu Cobalt ferrite (CoFe2O4) has been reported by various scientists as a spinel ferrite with high stability, reasonable saturation magnetization and high coercivity value. Cobalt ferrite unit cell possess a closed packed lattice structure with two types of crystallographic sites viz tetrahedral (A) sites and octahedral (B) sites. The two sublattices enclose antiparallel position with respect to each other. Therefore, differences in the magnetic moments of octahedral B-sites and tetrahedral A-sites result in the intrinsic magnetic properties of the ferrite. When we replace different metals in the CoFe2O4 lattice, alteration in the cation distribution influence the electro-magnetic properties of mixed ferrite. The electrical properties of the ferrite materials may be easily engineered as they rely on the chemical composition, annealing temperature and method of preparation. In the present paper, diamagnetic calcium ion as a dopant has been used for the formation of mixed ferrites. The sol-gel method as the synthesis route has many advantages as pure, single phase, highly crystalline pure and doped ferrites can be synthesized at a lower temperature and in lesser time as reported in the literature. 2. EXPERIMENTAL Stoichiometric amounts of the reactants were weighed and dissolved separately in minimum amount of distilled water. The molar ratio of respective metal nitrates to urea was taken as 1:1. All the individual solutions were then mixed together and ammonia solution was added dropwise with continuous stirring to adjust the ph at 5 7. The resultant solution was kept on a hot plate magnetic stirrer at o C till gel was formed. After a few minutes, the gels self-ignited in an auto combustion manner and the whole urea complex was utilized to yield fine ferrite powders [2]. The as obtained ferrite powders were annealed at 600 o C in a muffle furnace for 2 h. Powder X-ray diffraction (XRD) patterns were recorded using a X Pert Pro spectrophotometer with Cu Ka radiation (k = Å). Magnetic measurements were performed on a Vibrating Sample Magnetometer (VSM, 155 PAR). The hysteresis loops were recorded at room temperature with maximum applied field up to 10,000 Oe. The electrical properties were studied using a two probe method. 3. RESULTS AND DISCUSSION 3.1. X-ray diffraction studies The powder XRD patterns of the different ferrite compositions ignited at 600 o C for 2 h were recorded at room temperature and are shown in Fig. 1. All the diffraction peaks observed for the ferrite samples have been indexed as face centered cubic unit cell (JCPDS card No ) with Fd-3m space group. The absence of extra peaks indicates that the synthesized samples have single-phase cubic spinel structure.

3 Magnetic and Electrical Properties of Calcium Doped Cobalt Spinel Ferrites. 233 The average crystallite size was evaluated from the line broadening of most intense peak (311) using the Scherrer relationship [3-5]. The average crystallite size has been found to be well within an error of ±2 nm and its values have been given in Table 1. It is observed that the lattice parameter increases with increase in Ca 2+ concentration. The increase in the value of lattice constant, a may be attributed to the fact that the ionic radius of Ca 2+ ion (0.65 Å) is larger than that of Co 2+ ion (0.64 Å) [6-10]. Fig. 1. Powder XRD patterns of pure and ca doped ferrites. Table 1. Electro-magnetic parameters for pure and doped ferrites. Conc. (x) Lattice constant (a) Ms (emu/g) Hc (Oe) DC resistivity (ρ X 10 7 ) (Ʊ m) Drift mobility (µd X ) Magnetic Studies: Various magnetic parameters for the different samples annealed at 600 o C have been recorded at room temperature. The typical hysteresis loops for ferrite samples annealed are shown in Fig. 2. As the doping increases, the saturation magnetization values increase from 2.5 emu/g to 5.9 emu/g. The increase in the value of saturation magnetization is attributed to the increase in particle size at high temperature.

4 234 Anu Fig. 2. Room temperature hysteresis loops of ferrites Electrical properties Electrical properties like conductivity, resitivity, drift mobility etc. give important information about conduction mechanism in the ferrite under observation. Verwey mechanism can be best used to explain the conduction mechanism in ferrites [11-16] on the basis of electron exchange between the atoms of same element present in more than one valence state. The probability of electrons hopping depends upon the differences between the ions concerned along with the activation energy. The D.C. electrical resistivity variation with temperature has been shown in Fig. 3 It was observed that in different ferrite compositions, the resistivity decreases with increase in temperature, indicating the semi conducting nature of the ferrite synthesized. Fig. 3. Variation of log ρ with temperature

5 Magnetic and Electrical Properties of Calcium Doped Cobalt Spinel Ferrites. 235 Drift mobility (µd) of the different ferrite samples has been calculated 100 o C. Fig. 4 reveals that in various ferrite compositions, the increase in temperature lead to increase in drift mobility values. It can be explained due to the increase in hopping of the charge carriers from one site to another with the increase in temperature [16]. On the other side, when the concentration of Ca 2+ dopant increases, the drift mobility decreases whereas the D.C. electrical resistivity with increases. Fig. 4. Variation of drift mobility with temperature. 4. CONCLUSIONS The results in the research work undertaken demonstrate the formation of pure, mono phasic, highly crystalline pure and doped ferrites at a relatively lower temperature and in lesser time. As the concentration of the Ca dopant increases, magnetic parameters show increase in magnetization values of the doped samples. Also, electronic properties show an increase with respect to the temperature applied. The D.C. electrical resistivity of the ferrite samples, measured using two-probe technique increases with increase in dopant concentration due to decrease in Fe 2+ Fe 3+ hopping. These ferrites formed with unique electro-magnetic parameters can be widely used in magnetic devices as magnetic tapes, computer cores, magnetic delivery devices and many more. ACKNOWLEDGEMENT The author acknowledges the expert opinion and research facility from Dr. BS. Randhawa, Professor, GNDU, Amritsar.

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