Room-temperature magnetic behavior of Bi-doped Co⁢0.6⁢Zn⁢0.4⁢Fe⁢2⁢O⁢4ferrite nanoparticles

Abstract

In this study, we examined the effect of Bi⁢3+ion substitution on the structural and magnetic properties of cobalt ferrite nanoparticles Co0.6Zn0.4Fe⁢2⁢−𝑥⁢Bi𝑥⁢O4 with nominal compositions of 𝑥= 0.0, 0.005, 0.008, 0.01, and 0.03 under applied magnetic fields of up to 6 T at room temperature. Hysteresis loop analysis reveals that the saturation magnetization (𝑀𝑠), coercive field (𝐻𝑐), and remanent magnetization (𝑀𝑟) exhibit significant variation with bismuth concentration. Notably, the coercivity shows a non-monotonic trend, increasing at low Bi contents and then decreasing at higher doping levels. The cubic magnetocrystalline anisotropy constant (𝐾1), derived from the “law of approach to saturation,” decreases from 2.32 × 106 erg/cm³ for x = 0 to 1.58 × 106 erg/cm³ for x = 0.03 at room temperature, indicating strong dependence on Bi substitution. Yafet–Kittel based analysis indicates the emergence and intensification of spin canting with increased Bi content, providing insight into the observed magnetic behavior. These results are discussed in relation to inter-particle interactions driven by thermal fluctuations during the synthesis process and the redistribution of Co⁢2+ ions between tetrahedral (𝐴) and octahedral (𝐵) sites induced by Bi⁢3+ doping. These results suggest that Bi-doped cobalt-zinc ferrite is a promising material for room-temperature applications, including magnetic sensors and actuators.