Effect of Cu2+ substitution on structure, morphology, and magnetic properties of Mg-Zn spinel ferrite

Objective: To prepare Cu doped Mg0:5􀀀xCuxZn0:5Fe2O4 (x = 0.0, 0.05, 0.1, 0.15,0.2 and 0.25) spinel ferrites materials and study the structure, morphology, and magnetic properties. Methods: Cu doped Mg-Zn spinel ferrites are magnetic and highly resistive materials. They were synthesized by the method of solid-state reaction and characterized by x-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared (FTIR), andvibrating sample magnetometer (VSM) for their structural, compositional,morphological, functional properties. They are with spinel structure under Fd-3m space group. Their crystallite size was 44.58 nm to 31.02 nm range after calcined at 1000 oC. Their spinel structure was confirmed with FT-IR analysis, whose absorption bands were 598.84 – 580.40 cm-1 and 405.35 - 402.15 cm-1 range for higher and lower frequency, respectively. The value of coercivity is in the range 146.33 - 9.427 Oe with the variation of content. The lower values of the coercivity indicated the soft ferrimagnetic nature of the synthesized materials. Findings/ Application: Substitution of non-magnetic Cu2+ ions strongly influenced the structural and magnetic properties of magnesium ferrites. 
Keywords: Cu doped MgZn ferrite; XRD; FTIR; FESEM; Coercivity

In the present study, the spinel ferrite with the generic formula Cu doped Mg 0.5−x Cu x Zn 0.5 Fe 2 O 4 (x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25) was prepared by the standard ceramic method. The structural and magnetic properties were investigated using x-ray diffraction, field effect scanning electron microscopy, infrared spectroscopy, and vibrating sample magnetometer.

Materials and Methods
MgO, ZnO, CuO, and Fe 2 O 3 were mixed in appropriate stoichiometric ratio, finely grounded for 3-4 h, pre-sintered at 800 • C for 5 h, again reground for 3-4 h and finally calcined at 1000 • C for 6 h and prepared Cu doped Mg 0.5−x Cu x Zn 0.5 Fe 2 O 4 (x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25) under solid-state reaction method. The discs-shaped pallet was prepared from the resultant powder with the hydraulic press's help under 6 ton/cm 2 pressure and finally sintered at 1200 • C for 4 h, and measured the magnetic properties. Every heating process was followed by cooling.
The structural data were studied XRD (PANalytical XPert PRO diffractometer with CuKα radiation and λ = 1.5402 Å also with a continuous scan step size of 0.008). The morphology data were studied Scanning Electron Microscope (Carl Zeiss, EVOMA 15, Oxford Instruments, Inca Penta FETx3.JPG instrument). The chemical bonding data were examined FTIR (IR Prestige21 Shimadzu). Finally, magnetic properties were studied VSM (1T).  (20) . The crystallite size and lattice parameter are listed in Table 1. Thus, the synthesized materials are in the nanoscale range, exhibiting the nanoparticle behaviors applicable in different technological outputs. The highest lattice parameter with the least crystallite size and such parameters impact not only the structure but also the magnetic and electrical properties.  The lattice constants (a) of the samples were calculated using standard relation (21) ,

X-ray diffraction studies
The lattice constant is increasing gradually with Cu content due to the larger ionic radius of the Cu 2+ (0.70 Å) than that of the Mg 2+ (0.65 Å) as shown in Figure 2 and agrees with previous literature (22) . The crystallite size of the synthesized Cu doped Mg-Zn ferrite powders was evaluated with the help of Debye-Scherrer's relation (23) , where λ , β , and θ are the radiation's wavelength, the full width half maximum (FWHM) of the XRD peak, and Bragg's angle.

FESEM studies
The room temperature morphological study of the present Cu doped Mg 0.5−x Cu x Zn 0.5 Fe 2 O 4 (x = 0.0, 0.5, 0.1, 0.15, 0.2 and 0.25) synthesized materials was carried out using a scanning electron microscopy. The obtained FESEM micrographs are presented in Figure 3. Using these images, grain size for all the samples was obtained. Further, a more significant part of pores is on the scale of grain size and located among them (24) . Some aggregates are also observed in the micrographs. From micrographs exhibited cubic crystals of uniform size with average values between 2.7 to 4.6 Ωm.
https://www.indjst.org/  Figure 4. They all have two prominent absorption bands ν 1 and ν 2, in 600 and 400 cm -1 , due to stretching of tetrahedral metal ionoxygen bonding and vibrations of oxygen perpendicular to the axis joining the tetrahedral ion-oxygen respectively, as listed in Table 2. In the present system, the band ν 1 is found in the range of 598.84-580.40 cm -1 , and the lower band is in the range of 405.35-402.15 cm -1 . The band positions obtained in the present case are found to be in the reported range (25) . Slight variation in the band positions is due to the present samples' preparation, grain size, and porosity. Further, the absorption bands ν 1 assigned to the tetrahedral site (A) are shifted towards the lower frequency side with an increase in the Cu substitution. The https://www.indjst.org/ band positions' variation can be attributed to the estimated cation distribution of the present ferrite samples (26) .

Magnetic properties study
The ceramically prepared Cu doped Mg 0.5−x Cu x Zn 0.5 Fe 2 O 4 (x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25) ferrite particles' magnetic properties were studied using vibrating sample magnetometer (VSM) (27) . All the measurements of the magnetic properties were carried out at room temperature. The hysteresis loops are shown in Figure 5. The saturation magnetization (M s ) and coercivity (H c ) were obtained from the hysteresis loops, and the obtained values as listed in Table 3 and variation are shown in Figure 6. The table shows that the saturation magnetization increases with an increase in Cu substitution x = 0.1 and decreases x = 0.25. The highest saturation magnetization for magnesium ferrite is found to be 53.51 emu/g (x = 0.1). The coercivity is found to reduce from 146.33 Oe to 9.427Oe with the substitution of Cu. This implies that Neel's model could explain the observed magnetic behaviour of the Cu doped Mg-Zn samples.  Neel's theory of ferrimagnetism suggests that the cations present on various sublattices in spinel structure have attractive minutes oppositely adjusted. The inverse spinel ferrites of the net magnetic moment mainly depend on the number of magnetic ions that occupy the tetrahedral and octahedral sites (28) . The Cu 2+ ions substituted in synthesized samples have a direct bearing on the coercivity. Ongoing investigations proposed that coercivity was influenced by microstrain, size dissemination, magneto crystallinity, attractive area size, and anisotropy (29,30) .

Conclusions
Cu doped Mg 0.5−x Cu x Zn 0.5 Fe 2 O 4 (x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25) ferrite are prepared by solid-state reaction method. The samples were of single-phase, cubic spinel structure according to XRD. The gradual increase in lattice constant values with Cu substitution is obviously due to the Cu's larger ionic radius than the Mg. SEM micrographs exhibited cubic crystals of uniform size with average values between 2.7 to 4.6 Ωm. Infrared spectroscopic studies supported the spinel structure of all the ferrites. VSM studies revealed that the saturation magnetization is increased with increased Cu substitution from their highest values, 53.51 emu/g to 19.66 emu/g, respectively. On the other hand, the coercivity decreases from 146.33 Oe to 9.427 Oe with an increase in substitution. Thus, the substitution of non-magnetic Cu ions in magnesium has strongly influenced the magnesium ferrite's structural and magnetic properties. https://www.indjst.org/