Synthesis, Characterizations, and Magnetic Properties of Mixed Spinel Mg 1-x Zn x Fe 2 O 4 Ferrites

Mixed spinel Mg 1-x Zn x Fe 2 O 4 ferrites (where x = 0, 0.2, 0.4, and 0.6) nanoparticles were synthesized by using microwave-assisted combustion route. As-synthesized powdered samples were checked by XRD analysis, field emission-scanning electron microscopy, and vibration sample magnetometer to investigate the structural, morphology, and magnetic properties, respectively. XRD results exhibited that the crystallite size increases with the decrease of Zn +2 ion concentration for series of mixed spinel Mg 1-x Zn x Fe 2 O 4 ferrite expect x=0.2. All the mixed spinel Mg 1-x Zn x Fe 2 O 4 ferrite has different grain sizes with uniform distribution also presence voids in the samples. Pure magnesium ferrite has a lower net magnetization value but when magnesium ions (Mg +2 ) are replaced by zinc ions (Zn +2 ) then the value of saturation magnetization increases.

importance. Spinel-type ferrites are a group of iron oxides as the main constituent, and metal oxides [2]. Due to their unique magnetic, thermal, electrical, and catalytic properties for hightech applications, mixed spinel ferrite nanoparticles (MSFNs) are the particular research topic for the researcher all over the world [3][4][5]. Soft ferrites have a cubic spinel structure consists of 8 units of the form of M 2+ Fe 2 3+ O 4 , where "M" is a divalent atom of radius between 0.80 Å to 1.0 Å, such as Mn, Mg, Cd, Fe, Zn, Cu, etc. Magnesium-Zinc ferrite is a soft mixed ferrite of magnesium-ferrite and zinc-ferrite. Magnesium occupies octahedral (B) sites and Zinc occupies tetrahedral (A) sites in the spinel-structure with unit of the form (Zn 2+ 1 The limiting case, (x=1) where x is the degree of inversion.is called normal spinel ferrite and the other limiting case, ( x=0) is called inverse spinel ferrite. For a random distribution x can have value in between 0 and 1 [6][7][8].
Mixed spinel ferrites is gaining much interest among researchers, Aswad and Mutlak [5] studied the effect of synthesized Co 1-x Cu x Fe 2 O 4 , through hydrothermal route on the growth of some pathogenic bacteria, Abdelhasan et al. [9] synthesized Co-Zn ferrite nano particles less than 50 nm by microwave combustion and hydrothermal methods as a biomedical application, Amar et al. [10] synthesized Zn-doped Co-ferrite (CoFe 1.9 Zn 0.1 O 4 ) magnetic nanoparticles via sol-gel method as a magnetic catalyst, and Manikandan et al [11] were synthesized powdered Mg-doped ZnFe 2 O 4 nanoparticles with mean size in the range of (15nm -43nm) by a microwave combustion route. Here, we demonstrate the series of mixed spinel ferrite Mg 1-x Zn x Fe 2 O 4 where x = ( 0, 0.2, 0.4, and 0.6) were synthesized via microwave combustion route that is usually performed in solution media. This method was chosen due to simplicity and short time reaction.

Experimental
High purity nitrate salts of (Zinc-Magnesium: Iron) [from HIMEDIA Co., India] were used as the raw materials to prepare mixed spinel ferrite nanoparticles with a molar ratio (1:2) by microwave combustion route technique. Each material was weighed separately in stoichiometric ratio and dissolved in a suitable quantity of de-ionized water then the solutions were mixed thoroughly using a magnetic stirrer for 20 minutes to complete dissolution until a red color slimy solution is obtained. Stoichiometrically amount of fuel (glycine) with the chemical formula (C 2 H 5 NO 2 ) was added[Glycine to nitrate ratio 0.33] to the mixture under stirring. After 20 minutes, a dark brown colored mixture was formed. The mixture in a crucible was put a microwave oven with an irradiation power of 800 Watt. In the microwaveassisted combustion, the precursor solution with fuel boiled and starting released a lot of gases of which CO 2 , NO 2 , and N 2 after dehydration accompanied by simultaneous decomposition. As the solution reached the point of spontaneous combustion, it started to burn and release heat, causing the solution to vaporize and turn into solid material. Finally, filter papers were used so that compound filtered. Powder that Product was washed via ethanol and distilled water for (3) times, dried at (70 ᵒC) for 2 hours. Finely mortar was used to grind the resulting powder to obtain fine powders.
The X-ray diffraction analyses were obtained from the (Shimadzu XRD 6000, Japan). Morphology and elemental analyses were examined with field emission-scanning electron microscope [TE-SCAN Mira3, France] for samples of x= 0, and FE-SEM device kind [FEI Nova Nano SEM 450] for samples of x = 0.2. 0.4, and 0.6. Finally, magnetic hysteresis for all ferrite samples were obtained with a vibrating sample magnetometer (VSM, MDK).

Structure and morphology characterization
Mg 1-x Zn x Fe 2 O 4 ferrite series samples [where x = (0, 0.2, 0.4 and 0.6)] which were synthesized by microwave-assisted combustion route, were analyzed ( for structure and elemental analysis) using X-ray diffraction techniques (XRD) and energy dispersion X-ray analysis as shown in Figure (1. a, b, c, d, and e ) Figure (1. a)] are indexed to (220), (311), (222), (400), (422), (511) and (440) which corresponds to the spinel phase of ferrite structure. Similar findings have been in other studies [12,13]. Our results of the XRD patterns were in agreement with the standard data (JCPDS PDF card No. 01-077-0011). From XRD pattern, it can be observed that the sample with x=0.4 crystalizes more than the other samples. This is may be due to the synthesis conditions such as reaction time in the microwave oven, or slower ignition of the exothermic reaction using microwave energy, which prevent the slower simultaneous decomposition of the metal nitrate, which enhances the formation of phase. The crystallite size and lattice constant were calculated from XRD line broadening of the highest peak (311) plane using Deby-Scherrer formula [14] is given in Table 1.  [17]. The elemental analyses for as-synthesized powdered samples of the mixed spinel are shown in Figure (1. b, c, d, and e). Fe, Mg, and O elements can be observed in Figure ( FE-SEM images also showed presence porosities in the samples which may be because of release of gases during the combustion process. By comparing the results of the present work with that Rahmar [18], it was found that as-synthesized samples by this route almost displayed agglomeration.

Magnetic Measurements
Information about saturation magnetization of the samples of the mixed spinel Mg 1- x Zn x Fe 2 O 4 ferrite where x = ( 0, 0.2, 0.4, and 0.6) was determined by using a vibrating sample magnetometer with an applied external field of (15x10 3 gauss) at room temperature, as shown in Figure 3. The magnetization curve showed the lowest saturation magnetization (25.97 emu/g) of the ferrite sample for x = 0. This low net magnetization value is mostly due to (Mg +2 ) moments at B-site only. thus, moments of Fe +3 from the A-sites and B-sites cancel each other, this behavior causes low magnetization value. Also, the magnetization curve in Figure 3 of the ferrite sample for x = 0.2, 0.4, and 0.6 shows increase in saturation magnetization as zinc ions (Zn +2 ) concentrations increases. As magnesium ions (Mg +2 ) are replaced by zinc ions (Zn +2 ), saturation magnetization changes. It is observed that the value of saturation magnetization increased as the substituting with zinc content increases from 49.51emu/g to 59.55 emu/g at as Zn +2 concentrations increase from x = 0.2 to x = 0.4. Saturation magnetization shows a decreasing trend for mixed spinel ferrite at x = 0.6 due to the ZnO secondary phase, which was also observed by other authors [19,20]. The explaining of this phenomenon is that Mg 0.4 Zn 0.6 Fe 2 0 4 has an inverted spinel crystal structure. The observed changes in saturation values with increasing the zinc content is illustrated as the specific basis for exchange interactions that occur between various ions at octahedral and tetrahedral sites in spinel ferrites, Similar results were obtained by Mirshekar et al [14] and Yahya et al [21]. Net magnetization arises from the variation between the magnetic moments at octahedral and tetrahedral sites. In nature, both divalent magnesium ions (Mg +2 ) and divalent zinc ions (Zn +2 ) are non-magnetic, where Zn +2 ions located in tetrahedral A site, while Mg +2 ion is located in the octahedral B site. When divalent Zinc cation is replaced by divalent magnesium cation, it forces Fe +3 ion at the octahedral site to migrate to the tetrahedral site which results in a decrease of the net magnetic moment, thus saturation magnetization (Ms) decreases with the decrease of magnesium content (increase zinc content). Our results are similar to those of Rahman et al. [19]. Generally, the smaller value of saturation magnetization is usually attributed to lattice defects, surface spin disorder, and the presence of a magnetically inert layer on the nanoparticles' surface. Iron ions in the superficial layer have a random orientation of their magnetic moments due to their broken bonds, resulting in a decrease in the overall magnetization of each individual nanoparticle [22]. Saturation magnetization of the mixed spinel Mg1-xZnxFe2O4 ferrite are given in Table 3.

Conclusion
In the present work, mixed spinel Mg 1-x Zn x Fe 2 O 4 ferrite, where x = ( 0, 0.2, 0.4, and 0.6), was synthesized using the microwave -assisted combustion route. It was found that: 1) Microwave-assisted combustion route that is usually performed in solution media has short time reaction and simplicity. 2) Lattice parameter increased linearly with increasing the Zn content, 3) the Mg 1-x Zn x Fe 2 O 4 ferrite showed S-shape hysteresis curve, 4)Pure magnesium ferrite has low net magnetization value but when magnesium ions (Mg +2 ) were replaced by zinc ions (Zn +2 ), an increase in saturation magnetization for mixed spinel ferrite at x = 0.2 and 0.4 was observed and then a decrease in saturation magnetization for inverted spinel ferrite at x = 0.6.