Magnetic properties of nanostructured spinel ferrites and nanocomposite Nd2Fe14B/𝛼-Fe permanent magnets

Pramana

A Narayanaswamy1¹ 

[1] Materials Science Centre, Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai 600 025, India$$

关键词: Ferrites;    superexchange interactions;    magnetic properties of nanostructures;    Mössbauer spectroscopy of solids.;   

DOI  :  

学科分类：物理（综合）

来源: Indian Academy of Sciences

【 摘 要 】

This paper presents some of the important magnetic properties of the nano-structured spinel ferrites such as Ni0.5Zn0.5Fe2O4 and Mn0.67Zn0.33Fe2O4 and also that of the nanocomposite Nd2Fe14B/𝛼-Fe permanent magnetic material. The increase in the magnetic transition temperature of Ni-Zn ferrite from 538 K in the bulk state to 592 K when the grain size is reduced to 16 nm is correlated to the enhancement in the AB super-exchange interaction strength because of an increase in the magnetic ion concentration in the A-site on milling, as shown by the EXAFS and in-field Mössbauer studies. The particle size has been tailor-made by varying the concentration of the oxidant in the case of Mn-Zn ferrite. The critical particle size for the superparamagnetic limit has been found to be 25 nm with an effective magnetic anisotropy constant of 7.78 kJ m-3 which is about an order of magnitude higher than that of the bulk ferrite. The exchange coupling is found to be strengthened in the nanocomposite magnet Nd2Fe14B/𝛼-Fe, when the grain boundary anisotropy is removed by thermal annealing and thus facilitating the enhancement of the energy product.

【 授权许可】

Unknown