Abstract Spinel ferrites have come a long way in their versatile applications. The ever growing applications of these materials demand detailed study of material properties and environmental considerations in their synthesis. In this article, we report the effect of temperature and applied magnetic field strength on the magnetic behavior of the cobalt nickel ferrite nano powder samples. Basic structural properties of spinel ferrite nano particles, that are synthesized by an environmentally benign method of auto combustion, are characterized through XRD, TEM, RAMAN spectroscopy. Diffuse Reflectance Spectroscopy (DRS) is done to understand the nickel substitution effect on the optical properties of cobalt ferrite nano particles. Thermo magnetic studies using SQUID in the temperature range 5 K to 400 K and room temperature (300 K) VSM studies are performed on these samples. Fields of 0Oe (no applied field: ZF), 1 kOe (for ZFC and FC curves), 5 kOe (0.5 T), 50 kOe (5T) (for M-H loop study) are used to study the magnetic behavior of these nano particles. The XRD,TEM analysis suggest 40 nm crystallites that show changes in the cation distribution and phase changes in the spinel structure with nickel substitution. Raman micrographs support phase purity changes and cation redistributions with nickel substitution. Diffuse reflectance study on powder samples suggests two band gap values for nickel rich compounds. The Magnetic study of these sample nano particles show varied magnetic properties from that of hard magnetic, positive multi axial anisotropy and single-magnetic-domain structures at 5 K temperature to soft magnetic core shell like structures at 300 K temperature. Nickel substitution effect is non monotonous. Blocking temperature of all the samples is found to be higher than the values suggested in the literature.

中文翻译：

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钴镍铁氧体纳米颗粒的温度依赖性和外加场强依赖性磁性研究：通过环境友好的方法合成

摘要 尖晶石铁氧体在其多功能应用方面取得了长足的进步。这些材料不断增长的应用需要对其合成过程中的材料特性和环境考虑因素进行详细研究。在本文中，我们报告了温度和外加磁场强度对钴镍铁氧体纳米粉末样品磁性行为的影响。通过对环境无害的自动燃烧方法合成的尖晶石铁氧体纳米颗粒的基本结构特性通过 XRD、TEM、拉曼光谱进行表征。漫反射光谱 (DRS) 是为了了解镍取代对钴铁氧体纳米颗粒的光学性能的影响。在 5 K 至 400 K 的温度范围内使用 SQUID 进行热磁研究，并对这些样品进行室温 (300 K) VSM 研究。0Oe（无外加场：ZF）、1 kOe（用于 ZFC 和 FC 曲线）、5 kOe（0.5 T）、50 kOe（5T）（用于 MH 回路研究）的场用于研究这些纳米颗粒的磁行为. XRD、TEM 分析表明 40 nm 的微晶显示了镍取代的尖晶石结构中阳离子分布和相变的变化。拉曼显微照片支持镍取代的相纯度变化和阳离子重新分布。粉末样品的漫反射研究表明富镍化合物有两个带隙值。这些样品纳米颗粒的磁性研究显示出与硬磁性不同的磁性，5 K 温度下的正多轴各向异性和单磁畴结构到 300 K 温度下的软磁核壳状结构。镍替代效应是非单调的。发现所有样品的封闭温度高于文献中建议的值。