BIBECHANA 19(1-2) (2022) 61-67 61 Correlation between the Magnetic and DC resistivity studies of Cu substituted Ni and Zn in Ni-Zn ferrites D. Parajuli1, 2*, N. Murali3, K. Samatha4 1Research Center for Applied Science and Technology (RECAST), Tribhuvan University, Kathmandu- 44613, Nepal 2Tri-Chandra Multiple Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal 3Department of Physics, College of Engineering (A), Andhra University, Visakhapatnam-530003, India 4Department of Physics, Andhra University, Visakhapatnam-530003, India *Email: deepenparaj@gmail.com Article Information: Received: May 04, 2021 Accepted: February 03, 2022 Keywords: Spinel Ni-Zn ferrite Isotropic Negative-temperature coefficient Multilayer chip inductors ABSTRACT Cu substituted Ni0.5-xCuxZn0.5Fe2O4 (x = 0, 0.05, 0.1, 0.15 and 0.2) samples is synthesized using the sol-gel auto-combustion process. They have a cubic spinel structure with crystallite size in the range of 29.01–42.68 nm. The increment in the copper content increases the DC conductivity. The electrical resistivity decrease with an increase in the temperature i.e. it has a negative temperature coefficient with resistance similar to semiconductors. The remnant ratios R obtained from VSM show their isotropic nature forming single domain ferrimagnetic particles. The results are compared with Ni0.5CuxZn0.5- xFe2O4 (x = 0 to 0.25). The resultant material Cu substituted Zn is more significant than that of Ni as indicated by its results and previous literature. DOI: https://doi.org/10.3126/bibechana.v19i1-2.46387 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons.org/licenses/by-nc/4.0/ BIBECHANA ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher: Department of Physics, Mahendra Morang A. M. Campus, TU, Biratnagar, Nepal mailto:deepenparaj@gmail.com https://doi.org/10.3126/bibechana.v19i1-2.46387 https://creativecommons.org/licenses/by-nc/4.0/ http://nepjol.info/index.php/BIBECHANA Parajuli et al. / BIBECHANA 19(1-2) (2022) 61-67 62 1. Introduction Microwave devices, magnetic recording, coating, etc. are the major applications of Ni- Zn spinel ferrites [1-3]. Their crystal structure supports them in tuning their microstructural and electromagnetic properties which are necessary for many advanced applications. They have M2+Fe2 3+O4 2- composition with transitional metal (M) in tetrahedral and Fe on the octahedral region of the nano ferrite. A vigorous study on their structural and magnetic properties with doping of several elements in Ni-Cu-Zn ferrites is increasing day by day [4- 6]. The core of Rotary Dy, transformer, and magnetic induction uses these types of ferrites. In some cases, the density, porosity, the interactions among the particles with canting effects affect their magnetic properties. Recently, we have studied the effect of Cu substitution on magnetic and DC electrical resistivity of Ni-Zn ferrites Ni0.5Zn0.5- xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4) [7], structural and morphological study of Cu substituted Ni/Zn in Ni-Zn ferrite comparatively [8, 9], Cd substituted Ni-Zn ferrites [10] and Ni substituted Co Zn ferrites [11]. They all have spinel structures with semiconducting nature. In the present study, Cu substituted nickel ferrites are prepared by the sol-gel method, and compare their magnetic and DC electrical properties with Cu substituted Zn in Ni-Zn ferrites synthesized from the citrate gel route [12, 13]. The Cu substituted Zn in Ni-Zn ferrites is appropriate for Multilayer Chip Inductor (MLCI) as magnetic material. 2. Methodology A. Materials The sol-gel method was used for the preparation of Ni0.5Zn0.5-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4). The nitrates of Nickel, Copper, Zinc, Iron and citric acid with 99.99% purity were used as starting materials and mixed in a 1:1 ratio. The solution was made clear with double distilled water. Liquid ammonia was added dropwise with magnetic stirring at 100oC for 4 hrs. for getting the neutral solution after it was made neutral by adding liquid ammonia. The solution was then decanted and dried for 40 hrs. at room temperature. The resultant was powdered and sintered in a muffle furnace at 800 °C for 4 h at 5o/min. B. Characterizations The structure of Ni0.5Zn0.5-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4) was studied with the help of an X-ray diffractometer (Rigaku Miniflex II) with CuKα radiation of 1.5406 Å. The morphological and compositional study was made with TESCAN, MIRA II LMH SEM, and attached Inca Oxford EDX. The functional group and room temperature magnetic properties were studied with FT-IR and EZ- VSM- models respectively. The disc-shaped pellets were made with the help of a hydraulic system of 5 tons of pressure incorporating a few drops of polyvinyl alcohol as a binder. Their flat surfaces were polished with gold to use as electrodes after being sintered at 800oC in a muffle furnace and used for the study of DC resistivity in two probe systems. 3. Results and Discussions A. Magnetic properties EZ-VSM used for the magnetic characterization of Ni0.5Zn0.5-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3 and 0.4). Ferrites have higher resistivity due to unequal antimagnetic moments giving rise to higher spontaneous magnetization. Moreover, they have a negative exchange integral affected by an interatomic distance which obstructs the flow of electrons [14]. However, their saturation permeability, coercivity, susceptibility, Curie temperature, etc. are affected by the density of ions in their respective interstitial sites and their structure determines the hysteresis loop's shape, resistivity, ac conductivity, and dielectric constant. The doping of either magnetic or nonmagnetic extrinsic elements changes their property accordingly. The magnetic saturation, coercivity, etc. are calculated from their hysteresis curves as shown in figure 1. The obtained values of Ms and Hc are listed in Table 1 [15]. Parajuli et al. / BIBECHANA 19(1-2) (2022) 61-67 63 Table 1: Ms and Hc of Ni0.5-xCuxZn0.5Fe2O4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites Concentratio n (x) Ms (emu/g) Hc (Oe) 0.0 73.26 45.36 0.05 80.66 60.62 0.1 83.86 84.45 0.15 56.05 65.26 0.2 46.32 51.48 From table 1, Ms increases up to (x ≤ 0.1) and then starts decreasing with Cu2+ concentration. This is due to the distribution of cations and exchange interaction. On adding copper ions to the Nickel-Zinc mixture, they exchange a few magnetic ions Fe3+ and Ni2+ in A and B- sites. The AB interaction is then increased thereby resisting antiparallel spin which ultimately raises the magnetic saturation [16]. According to Weiss's Molecular field theory, the mixed interaction (A-B and B-A) is more than similar A-A and B-B interaction resulting from the hysteresis loop [17]. The increment of nonmagnetic Cu ion in place of Zn ion decreases saturation magnetization. The occupancy of the B site by Cu ion helps Fe3+ ions migrate to the A-site thereby reducing magnetization in the B site and increasing in the A site. The total magnetization is obtained using Neel’s [18] law, according to which M=|MB − MA|. So, the Cu substituted Zinc effectively works in changing the magnetic properties of the sample than Nickel. B. DC Electrical Resistivity There is a rapid, then steady and finally constant decrease of DC resistivity of Cu substituted Nickel in Ni-Zn ferrites nanoparticles with Cu concentration [19] as shown in DC resistivity vs. temperature for the Cu substituted Ni-Zn ferrite of figure 3. A straight line is obtained from the logeρ vs. 1000/T graph showing the semiconducting nature of the ferrites under consideration. The temperature variation of DC electrical resistivity of Ni0.5Zn0.5−xCuxFe2O4 ferrite samples as in figure 4 indicates that all the samples have semiconducting properties. Further, the temperature-dependent resistivity varied larger with the concentration of Cu ion and seems more effective for x=0.15 in the case of Cu substituted zinc in Ni-Zn ferrite. So, the resistive property is changed effectively in Cu substituted zinc in Ni-Zn ferrite than that in Cu substituted nickel. Figure 1: Hysteresis curves of Ni0.5- xCuxZn0.5Fe2O4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrite NPs at room temperature Figure 2: Hysteresis curves of Ni0.5Zn0.5−xCuxFe2O4 (x=0.00 to 0.25) at room temperature [12] C. Activation energy calculation The slope of the tangents on the plot of 1000/T versus logeρ of Ni0.5Zn0.5−xCuxFe2O4 is used for the calculation of their activation energies where we use the Arrhenius relation Parajuli et al. / BIBECHANA 19(1-2) (2022) 61-67 64 incorporating the dynamism of hopping charge carriers due to temperature [19] as: 𝛒 = 𝛒𝐨𝐞 ( ∆𝐄 𝐊𝐓 ) (1) where, ρ and ρo are the dc electrical resistivity at temperature T and absolute zero. ∆E and K are the activation energy and the Boltzmann constant. The activation energies obtained are plotted against the concentration of the Cu in Ni0.5Zn0.5−xCuxFe2O4 are shown in figure 5. Figure 3: Temperature dependence of DC resistivity of Ni0.5-xCuxZn0.5Fe2O4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) ferrites Figure 4: 1000/T versus logeρ of Ni0.5Zn0.5−xCuxFe2O4 samples (x = 0.00 to 0.25) [13] The variation in resistivity of the samples is according to the Verwey and de Boer hopping mechanism in which the electrons of the same element jump at their different valence states. As a result, Fe2+ Fe3+ hopping is raised for higher sintering temperature as more Fe2+ ions. The Ni2+  Ni3+ and Cu3+  Cu2+ hopping can also take place simultaneously [21]. Figure 5: Activation energies Vs. Concentration (x) of the Ni0.5-xCuxZn0.5Fe2O4 (x = 0.0, 0.05, 0.1, 0.15 and 0.2) Figure 6: Cu concentration vs. logeρ & Ea of Ni0.5Zn0.5−xCuxFe2O4 (x = 0.00 to 0.25) [13] Figure 6 shows the variation of activation energies and DC resistivity with Cu substituted zinc concentration in Ni0.5Zn0.5−xCuxFe2O4 nanocrystalline ferrite samples (x = 0.00 to 0.25). From the Figure, it is observed that the Parajuli et al. / BIBECHANA 19(1-2) (2022) 61-67 65 activation energies and resistivities of the samples are fluctuated more than that in Cu substituted nickel in NiZn ferrites but in the range of 0.53 eV to 0.67 eV. 4. Conclusion The structures of the nanocrystalline Ni0.5- xCuxZn0.5Fe2O4 (x = 0.0, 0.05, 0.1, 0.15, and 0.2) ferrite NPs were synthesized by Sol-gel auto-combustion method and confirmed their structure to have single-phase cubic spinel ferrite with the help of XRD and FTIR. The magnetic measurements show that saturation magnetization, coercive forces, and activation energy are highest at x = 0.1. While the conductivity is lowest at x=0.05 in the case of Cu substituted nickel. The Zinc content effectively works in changing the magnetic properties of Nickel. Both have isotropic magnetism. In both cases, the electrical resistivity decrease with an increase in the temperature i.e. it has a negative temperature coefficient with resistance similar to semiconductors. The activation energies are varied more in the range 0.53 eV to 0.67 eV in Cu substituted zinc than that in the range 0.42 to 0.51 eV. The variation in Cu substituted nickel and Cu substituted zinc synthesized by two different processes are due to their different (a) density and porosity (b) super- exchange interactions (bond angles and lengths) and (c) spin canting effects. The values agree well with our and other previous calculations. 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Lett. 7(1)(2012)1–14. https://doi.org/10.1186/1556-276X-7-112 https://doi.org/10.1186/1556-276X-7-112 *Email: deepenparaj@gmail.com A. Materials The sol-gel method was used for the preparation of Ni0.5Zn0.5-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4). The nitrates of Nickel, Copper, Zinc, Iron and citric acid with 99.99% purity were used as starting materials and mixed in a 1:1 ratio. The soluti... B. Characterizations The structure of Ni0.5Zn0.5-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4) was studied with the help of an X-ray diffractometer (Rigaku Miniflex II) with CuKα radiation of 1.5406 Å. The morphological and compositional study was made with TESCAN, MIRA II LM... 3. Results and Discussions