Optimizing the low coercivity of Ni-Cu doped lithium ferrites for multilayer chip inductors

Abstract

This research investigates the effectiveness of lithium ferrites co-doped with nickel (Ni) and copper (Cu) in multilayer chip inductors, a key component in microelectronic devices. “Li_0.5-x/2(Ni_0.5Cu_0.5)_xFe_2.5-x/2O₄ (0.0 ≤ x ≤ 1.0),” Ni and Cu co-substituted lithium ferrite (LNCF) was synthesized using an economical sol-gel method and sintered at 1100 °C. XRD investigations revealed the formation of a single-phase spinel structure, with a lattice constant “a” in the range of 8.364–8.284 Å. A reduction in the lattice constant “a” and unit cell volume “V”and a decrease in hopping lengths (LA and LB) were observed with Ni-Cu, accompanied by increased porosity. The crystallite size “D” initially increases and decreases with the rising doping concentration. The SEM images revealed the presence of aggregated nanoparticles suitable for low-coercivity multilayer chip inductors. Magnetic parameters such as saturation magnetization (M_s), remanence (M_r), coercivity (H_c), squareness ratio (S.R.), and anisotropy constant (K) have been measured from hysteresis loops. The observed highest value of M_s was 7.88 emu/g for the synthesized LNCF with x = 1.0. The H_c value falls within a few hundred Oe range, which is crucial for multilayer chip inductor applications. Moreover, S.R. < 1, which indicates a single-domain structure of LNCF. The magnetoresistance was more significant when a magnetic field was applied than when it was not. A progressive decline in the magnetic susceptibility (\({\chi }_{m}\)) of all the synthesized spinel ferrites was observed as the temperature increased due to the disorder of spin orientation at the Curie temperature (T_c). The noted T_c value of all samples ranged from 433 to 453 K. This research highlights Ni-Cu co-doped lithium ferrites endowed with multiple functionalities, making them ideal candidates for applications such as multilayer chip inductors and recording media.

Graphical Abstract