Co2+ Substituted Spinel MgCuZn Ferrimagnetic Oxide: A Highly Versatile Electromagnetic Material via a Facile Molten Salt Route

We report on the electromagnetic properties of Co2+ substituted spinel MgCuZn ferrites developed via a facile molten salt synthesis (MSS) route. The choice of synthesis route in combination with cobalt substitution led to strong electromagnetic properties such as high saturation magnetization (i.e., 63 emu/g), high coercivity (17.86 gauss), and high initial permeability (2730), which are beneficial for the multilayer chip inductor (MLCI) application. In a typical process, the planned ferrites were synthesized at 800 °C using sodium chloride as a growth inhibitor, with dense morphology and irregularity in the monolithicity of the grains. The compositional analysis of as-prepared ferrite confirms the presence of desired elements with their proportion. The crystallite size (using X-ray diffraction (XRD) analysis) for different samples varies in the range of 49–51 nm. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis showcases the compact morphology of the developed samples, which is typical in the ferrite system. The dielectric properties (dielectric-loss and dielectric-constant) in the frequency range of 100Hz–1MHz suggest normal dielectric distribution according to interfacial polarization from Maxwell–Wagner. From the developed ferrites, upon comparison with a low dielectric loss with high permeability value, Mg-Cu-Zn ferrite with Co = 0.05 substitution proved to be a stronger material for MLCIs with high-performance applications.


SI 1. Characterization of the material
The ferrites were characterized by XRD, The XRD pattern, SAED; ED's analysis confirmed the spinel cubic structure and indicated the absence of any other impurity phase.
The X-ray diffraction (XRD) pattern of the samples were obtained on BRUKER D8 advanced X-ray diffractometer using Cu-Kα (λ=1.54056 Å) radiation at 2θ values between 20º and 80°.
The interplanar distance d (Å) was calculated using Bragg's law. The lattice parameter 'a' was calculated using the relation: Where 'a' is the lattice constant, (h k l) are the Miller indices and 'd' is the interplanar distance.
The average crystallite size (t) of the sintered powder was estimated using the Scherrer equation: Where 'β' is the full width at half maximum (FWHM) for the most intense (311) reflection, 'θ' the angle of reflection, and 'λ' the wavelength of X-ray radiation used. The bulk density (ρm) was determined using the formula: Where m is the mass, r is the radius and h is the height/thickness of the pellet sample. The Xray density (ρx) of the prepared samples was calculated from the relation: where 'Z' is the number of molecules per unit cell, which is 8 for the spinel cubic structure, 'M' is the molecular weight of the samples; 'N' is the Avogadro's number and 'a' is the lattice constant. Percentage porosity (P) of the samples was calculated from ρm and ρx values using the expression: Scanning electron microscope (Model SEM-JEOL) operating at 5 kV was used to examine the surface morphology of the samples. Transmission electron microscope (TEM) images were taken by using a Philips CM 200 FEG microscope equipped with a field emission gun at an accelerating voltage of 200 kV, with a resolution of 0.24 nm.
The silver electrode paste was applied on two surfaces of the sintered pellet for dielectric, and electric property measurements. DC electrical resistivity measurements were carried out with two probe method using laboratory designed cell. We had measured the resistance of the sample as function of temperature. The pellet was mounted in a sample holder consisting of two silver rods in which the sample can be sandwiched with the help of screws.
The cell was placed in a temperature controlled tube furnace. A calibrated chromel-alumel thermocouple was used to measure the temperature of the tube furnace. The electrical resistivity was determined using the relation: Where 'r' is radius, 't' is the thickness and 'R' is the resistance of the sample. Magnetization measurements of the powder samples were carried out using vibrating sample magnetometer (Lake Shore 7410 VSM). The magnetic hysteresis loops were measured with an applied magnetic field of 20 kOe. The susceptibility measurements were carried out on powder sample using double coil set up [39]. The toroid samples with outer diameter of 2.5 cm, inner diameter of 1.5 cm and thickness of 0.3 cm having 100 turns of winding were used for the inductance measurement. The inductance measurements were carried out from room temperature up to 350 ºC at 1 kHz using a computer controlled impedance analyzer (Hioki Model 3532-50 LCR HI Tester, Japan). Also the frequency dispersion of initial permeability was studied in frequency range 100 Hz to 5 MHz at room temperature. The initial permeability was determined from inductance measurements of coils using the formula: = 0.0046 ℎ Where 'd2' is the outer diameter, 'dl' the inner diameter, 'L' the inductance in µH, 'h' the height in inches and µi the initial permeability. The dielectric measurements at room temperature were carried using LCR-Q meter (HP-4284A). The Curie temperature values (Tc) were determined from the temperature variations of susceptibility and initial permeability curves.