Theoretical study of the electronic and magnetic behavior of Ca-Doped Ni–Zn Ferrites

Introduction
The cubic spinel structure gives Ni–Zn ferrites low cost, simple synthesis, and favorable magnetic properties [1]. Ca and Zn substitution in nickel ferrites has attracted considerable attention because of its strong influence on magnetic behavior. Some studies further suggest that low concentrations of substituted ions may induce superparamagnetic features in nanosized ferrites because of reduced magnetic anisotropy [2]. On the other hand, increasing Ca content can decrease saturation magnetization, since non-magnetic Ca²⁺ ions weaken the A–B superexchange interactions within the spinel lattice [3].

Methods
The characteristics of nickel-ferrite and their influence on Ca doping, together with atomistic modeling and electronic-structure analysis using density functional theory, were explored. The interaction between ions and electrons was described by the projector augmented wave method. To achieve reliable results, a plane-wave basis set with a suitable energy cutoff and a dense Monkhorst–Pack k-point grid was employed for the electronic structure calculations.

Discussion
The electronic structure calculations reveal that Ni0.32Zn0.58Ca0.10Fe2O4 exhibits semiconducting behavior with a band gap of 1.08 eV. The absence of electronic states is observed at the Fermi level, confirming its non-metallic nature. The relatively narrow band gap is expected to facilitate charge carrier excitation, making this ferrite more favorable than conventional ferrites for electronic applications.

Conclusion
The theoretical results show that Ca-doped Ni–Zn ferrites possess stable semiconducting behavior together with favorable magnetic characteristics. The work illustrates that calcium incorporation is an effective approach for tuning the electronic and magnetic performance of Ni–Zn spinel ferrites for potential multifunctional material applications.

1. S.Mammadova et al., “Density Functional Theory Perspective on Zn Adsorption on the NiFe2O4 (001) surface” Advanced Physical Research, v.8, 2026.
2. S.Sun et al., “Monodisperse MFe₂O₄ (M = Fe, Co, Mn) nanoparticles” Journal of the American Chemical Society, 126 (2004) 273–279.
3. M.Abbas et al., “Effect of Ca substitution on structural and magnetic properties of Ni–Zn ferrites” Ceramics International, 39 (2013) 5129–5136.