Enhancement of maximum energy product in exchange-coupled BaFe12O19/Fe3O4 core-shell-like nanocomposites

• Published in: Journal of alloys and compounds Vol. 806; pp. 120 - 126
• Main Authors: Mohseni, Farzin, Pullar, Robert C., Vieira, Joaquim M., Amaral, João S.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.10.2019; Elsevier BV
• Subjects: BaFe12O19; Barium hexaferrite; Corrosion resistance; Exchange-spring magnets; Ferrites; Heat exchange; Heat treatment; Hexagonal ferrite; High resistance; Iron oxides; Magnetic exchange coupling; Magnetic saturation; Magnetism; Magnetite Fe3O4; Nanocomposite hard magnets; Nanocomposites; Nanoparticles; Optimization; Oxidation resistance; Permanent magnets; Phase ratio; Rare earth elements; Remanence; Sol-gel processes; Nanocomposite hard magnets; Magnetite Fe3O4; Hexagonal ferrite; BaFe12O19; Magnetic exchange coupling; Exchange-spring magnets
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.07.162

Recent economic and environmental concerns have prompted intensive research on the development and optimisation of rare-earth free permanent magnets, in particular of ferrites. M-type barium hexaferrites (BaFe12O19, BaM) are a type of technologically important, low-cost permanent magnet, with high Tc and high resistance to oxidation and corrosion. Their magnetic performance can be improved upon by exploring exchange-coupling mechanisms, to increase their competitiveness with existing rare-earth magnets. The present investigation explores core-shell-like BaM/Fe3O4 nanocomposites, where BaM flake-like particles where prepared via the sol-gel auto-combustion method, and then coated by magnetite spinel nanoparticles via a hydrothermal method, requiring no post-heat treatment. We show how optimised hard to soft magnetic phase ratio and preparation conditions lead to a significant enhancement to the saturation magnetization and remanence, and consequently to an increase of over 75% in the maximum energy product, compared to the parent BaM hexagonal ferrite compound. •BaM powders were coated with Fe3O4 NPs via a hydrothermal method.•Achieving Optimised exchange-spring behaviour in BaM/Fe3O4 nanocomposite.•Their magnetic properties were studied and compared to commercial BaM powder.•30% increase in Ms and (BH)max of the nanocomposite compared to a commercial BaM.•Increase in (BH)max compared to recent reports on the same family of nanocomposites.