Influence of substitutions and Sintering Aids on Structural and Electromagnetic Properties of NiCuZn Ferrite

Abstract

NiCuZn ferrite is the most important magnetic materials used for the manufacturing of multilayer chip inductors. The present work is focused on the influence of substitutions and sintering aids on electromagnetic properties of NiCuZn ferrite. (Ni0.8−xCu0.2Znx)Fe2O4 ferrites with 0.45≤x≤0.60 compositions were studied to
optimize Zn concentration. The effects of Mg2+ substitution for Ni2+ and La3+, Sm3+ substitutions for Fe3+ on the electromagnetic properties of optimized NiCuZn ferrite
were investigated. The effects of sintering aids like V2O5, Bi2O3 and MoO3 on the densification kinetics and electromagnetic properties of the ferrite were also
investigated. Ferrite specimens were synthesized by nitrate-citrate sol-gel auto combustion process. Nanocrystalline ferrite powder was successfully synthesized by self
propagating combustion method. The process resulted in the formation of nano-sized (19-22 nm), highly reactive (specific surface area- 40-50 m2/gm) and crystalline
spinel ferrite powders. The ferrite powders also showed good sinterability at around <950°C. On the basis of good permeability as well as resistivity,Ni0.25Cu0.2Zn0.55)Fe2O4 composition was optimized. The composition showed, initial
permeability of about 111 and the resistivity of about 8.9 MΩ-cm at 100 kHz with frequency stability up to ~10 MHz.
An improved electromagnetic property of the Mg substituted ferrite was found in (Ni0.07Mg0.18Cu0.2Zn0.55)Fe2O4 nominal composition. The initial permeability, saturation magnetization and resistivity were of about 2420, 85 emu/gm and 10 MΩ- cm at 100 kHz respectively in this composition. The improved electromagnetic properties of the composition might be due to the lowering of magnetostriction
constant by Mg substitution and partly due to better densification. La substitution in the ferrite mainly produced grain boundary secondary phase LaFeO3. However, bulk density and grain size of the ferrite increased with La
vii substitution up to 3.75 atom%. A significant increase in initial permeability (~ 424),saturation magnetization (~ 66 emu/gm) and resistivity (~ 69 MΩ-cm at 100 kHz) was
found in (Ni0.25Cu0.2Zn0.55)La0.025Fe1.975O4 composition. The increased permeability might be due to the combined effect of increased grain size, increased densification,
decreased anisotropy and compressive macro-stresses, etc. The La solubility in the ferrite lattice was very low (~ 0.1 atom/unit cell). The Sm substitution showed the formation of secondary phase SmFeO3 in the ferrites. Bulk density and grain size of the ferrites increased with increasing Sm substitution up to 2.5 atom%. Electromagnetic properties were maximized in (Ni0.25Cu0.2Zn0.55)Sm0.05Fe1.95O4 composition. An initial permeability of about 312,saturation magnetization of about 70 emu/gm and resistivity of about 54 MΩ-cm at 100 kHz were measured in the composition. V2O5 exhibited better densification behavior among all sintering aids with an
onset sintering temperature of ~ 825°C. The electromagnetic properties of the ferrite were also better in this V2O5 doped ferrites.