Giant exchange bias and exchange enhancement observed in CoFe2O4-based composites

• Published in: Journal of alloys and compounds 2013-12, Vol.581, p.263-269
• Main Authors: Zan, F.L., Ma, Y.Q., Ma, Q., Xu, Y.F., Dai, Z.X., Zheng, G.H.
• Format: Article
• Language: English
• Subjects: Alloys; Annealing; Antiferromagnetism; Applied sciences; Bias; Co/Fe alloy; CoFe2O4 ferrite; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Exchange bias; Ferrimagnetics; Ferrimagnetism; Heat treatment; Hydrothermal reaction; Iron; Magnetic properties and materials; Metals. Metallurgy; Physics; Post-annealing; Precursors; Production techniques; Solid solutions; Studies of specific magnetic materials
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2013.07.062

Giant exchange bias (HE=2233Oe) and significant coercivity enhancement (HC=10153Oe) have been observed below the Néel temperature of Co3O4 among samples annealed in air, resulting from the coupling between ferrimagnetic CoFe2O4 and antiferromagnetic Co3O4 phases. [Display omitted] •Giant exchange bias (HE=2233Oe) and significant coercivity enhancement were observed.•By reducing the precursor powders in H2 ambient, Co3Fe7 was obtained, with the MS value232emu/g.•The magnetic parameters can be sensitively tuned by processing conditions. Precursor powders, containing mainly CoFe2O4 and Co(OH)2, have been hydrothermally synthesized and then annealed in either air to obtain a ferrimagnetic CoFe2O4/antiferromagnetic Co3O4 composite, or H2 ambient to reduce the precursors to Co/Fe alloy. Giant exchange bias (HE=2233Oe) and significant coercivity enhancement (HC=10153Oe) were observed below the Néel temperature of Co3O4 in samples annealed in air, resulting from the exchange coupling between ferrimagnetic CoFe2O4 and antiferromagnetic Co3O4 phases. By reducing precursor powders in H2 ambient, a solid solution of Fe and Co (Co3Fe7) was obtained; the average atomic moment for Co3Fe7 is 2.4μB, larger than that of separated Fe or Co. We also show that the magnetic parameters can be sensitively tuned by varying processing conditions, which may be useful for obtaining the desired magnetic performance.