COMPARISON OF Ni 0.6 Co 0.4 Fe 2 O 4 AND NiFe 2 O 4 NANOPARTICLES FOR MAGNETIC CHARACTERISTICS, SYNTHESIZED USING CO-PRECIPITATION METHOD

Comparison of nickel Ni 0.6 Co 0.4 Fe 2 O 4 and NiFe 2 O 4 were studied. The co-precipitation method was performed for the whole sample. After annealing of 600  C for 4 hours, the nanoparticles samples evaluated their structural properties by using Fourier Transform Infra-Red (FTIR) and X-Ray Diffraction (XRD). The XRD pattern confirms that the whole samples have the crystalline structure of the face-centered cubic (fcc) inverse spinel. Furthermore, the lattice and crystallite size of NiFe 2 O 4 increased when added Co 2+ . The FTIR spectrum showed two prominent absorption bands, i.e., at around k of 358 cm -1 and 588 cm -1 , where metals at tetrahedral and octahedral sites reflect intrinsic vibrations, respectively. Finally, the decrease of saturated magnetization M S from 22.2 emu/g and 9.92 emu/g replacement of Co 2+ cation with Ni 2+


INTRODUCTION
Due to technological interests and attractive magnetic properties, the synthesis of spinel ferrite nanoparticles is becoming one of the most popular research fields. One essential spinel ferrite is cobalt ferrite which exhibits relatively high curie, high magnetostrictive coefficient, and appropriate saturation magnetization and electrical insulation [1][2][3] . These promising properties of cobalt ferrite allow it to be applied in various fields of high-density digital recording devices [4] , medical applications [5] , catalysts [6] , and others. In addition to its interesting application, changing the magnetic properties of cobalt ferrite can be done by adding doping to replace the ions in divalent or trivalent ions [7][8] . As in the research conducted by Kwang Joo Kim et al., it was found that the Ni0.5Co0.5Fe2O4 thin films made by the sol-gel process have spinel structure with lattice parameters that were slightly smaller by 0.1% compared to CoFe2O4. Where Co ions occupy the tetrahedral and octahedral sites, while Ni ions occupy most of the octahedral sites of the spinel lattice. Saturation magnetization, remanent magnetization, and Coercive field of Ni0.5Co0.5Fe2O4 were reduced to 62%, 68%, and 29% [9] .
Nickel ferrite (NiFe2O4) nanoparticles are ferrite spinel magnetic nanoparticles with properties such as low melting point, high specific heating, expansion coefficient is large, saturation magnetic moment low magnetic transition temperature [10][11] . NiFe2O4 nanoparticles are cubic ferromagnetic oxides with high permeability at high frequencies and high electrical resistance [12] . NiFe2O4 nanoparticles exhibit ferromagnetic properties due to the anti-parallel magnetic moment pairing between the magnetic moments of Fe 3+ ions in the tetrahedral position. with the magnetic moments of Ni 2+ ions and Fe 3+ ions in the octahedral position. This ferrite system's remarkable electrical and magnetic properties depend on the properties of the ions, and the distribution between the tetrahedral and octahedral positions. NiFe2O4 nanoparticles are soft ferrite material with characteristic ferromagnetic properties, low conductivity and low eddy current losses, high electrochemical stability, catalytic behavior and are widely available in nature [15] . NiFe2O4 and CoFe2O4 have an inverted spinel structure where (Ni 2+ Co 2+ ) [Fe2 3+ ] O4 2generally Fe 3+ are in octahedral and tetrahedral sites while Ni 2+ and Co 2+ are in octahedral sites [16] .
There are two categories of 'bottom-up' and 'top-down' spinel ferrite synthesis methods. During 'bottom-up,' particles are formed when ions chemically combine. In the 'bottom-up, there are many synthesis techniques: the co-precipitation technique. Co-precipitation is widely used because it is cost and time-efficient, environmentally friendly, and has high mass production [17][18] . This research will discuss the comparison of Ni0.6Co0.4Fe2O4 and NiFe2O4. The NixCo1-xFe2O4 nanoparticle samples were synthesized using the coprecipitation method. Fourier transform infra-red (FTIR), x-ray diffractometer (XRD) were used to characterize the samples obtained, and magnetometry sample (VSM).

Material
All the materials used in this report are of analytical grade and used without further purification Ni(NO3)2, Co(NO3)2.6H2O, Fe (NO3)3.9H2O, and Sodium hydroxide.

Synthesis of Ni0.6Co0.4Fe2O4 and NiFe2 O4
The synthesis process is carried out through co-precipitation techniques, dissolving Ni(NO3)2, Co(NO3)2.6H2O, and Fe(NO3)3.9H2O for Ni0.6Co0.4Fe2O4 nanoparticles. Whereas NiFe2O4 nanoparticles, made by dissolving Ni(NO3)2 and Fe(NO3)3.9H2O each with 200 ml of aqua-bides. Furthermore, it stirred using a magnetic stirrer at a speed of 300 rpm and heated at 350°C above the hot plate until it reached a temperature of 95°C. Then, the titration process is carried out by mixing 4.8 M NaOH into the solution (drop by drop). During the titration process, the solution temperature is maintained at 95°C. The synthesis solution is deposited for one night, then washed six times using ethanol and distilled water. Then, the precipitate was dried using an oven for 12 hours with a controlled temperature of 100°C and crushed to fine by mortar. Samples of Ni0.6Co0.4Fe2O4 and NiFe2 O4 were in a furnace with 600°C aneling temperature variations and then crushed again for homogeneous results.

Characterizations studies
The Ni0.6Co0.4Fe2O4 and NiFe2 O4 samples that had been formed were then characterized. The structural properties of samples were characterized using Cu-Kα, radiation ( = 1.54 Å) for X-Ray Diffraction (XRD) D8 Advance Diffractometer, Bruker, USA. The 2 range was set at 25-70° with a step size of 0.02. The oxide bonds of the sample were characterized by Fourier Transforms Infrared (FTIR) spectroscopy (Shimadzu IR Prestige 21). The FTIR was recorded in the range 400-4000 cm -1 . Where λ is the X-ray wavelength (1.540 Å), β is full width at half maximum (FWHM), and θ is the diffraction angle. Table 1 gives the increase in crystal size (D) in the presence of Cobalt ferrite, lattice parameter (a) of all samples calculated individually using the formula where d is the interplanar distance between two planes and (h, k, l) are the Miller indices. The lattice parameter value increased with the addition of cobalt ferrite from 8.85 to 13.81. This is caused by the fact that Co 2+ has a larger ionic radius (0.74 Å) than Ni 2+ (0.69 Å), having a smaller ionic radius, which causes unit cell contraction. The X-ray densities ( ) was obtained from the equation where M is the molecular weight of the sample, N is Avogadro's number. Intesity(a.u) related to the crystal size of the sample. Lattermost, the nickel ferrite strains decreased from 8.85×10 −3 to 13.81×10 −3 with the addition of cobalt ferrite.

FTIR analysis
FTIR characterization for the analysis of the oxide bond of Ni0.6Co0.4Fe2O4 and NiFe2O4 samples ( Figure 3) with a range of 4000 cm -1 -350 cm -1 . Characteristic of the observed curves for spinel ferrite, wave number v1 is in the range of 600 cm -1 -500 cm -1 and wavenumber v2 is around 450 cm -1 -380 cm -1 , which corresponds to the stretching of bonds between metal ions and oxygen at the tetrahedral and octahedral sites [17] . The absorption peaks observed for Ni0.6Co0.4Fe2O4 and NiFe2 O4 were around 588.3cm -1 -558.42 cm -1 for the tetrahedral site and 376.14 cm -1 -358.78 cm -1 for the octahedral site.

VSM analysis
The comparison of hysteresis loops between sample Ni0.6Co0.4Fe2O4 and NiFe2O4 has the same typical width and different saturation points ( figure 3). Sample Ni0.6Co0.4Fe2O4 has a larger hysteresis than NiFe2O4. Table 3 shows the presence of the enhancement in Ms, Hc, and Mr, of Ni0.6Co0.4Fe2O4, compared to NiFe2O4. The presence of cobalt ion increased the Mr and Ms of nickel ferrite from 1.96 emu/g to 12.33 emu/g and 9.92 emu/g to 22.2 emu/g.