Mechanochemical Synthesis of Nanocrystalline (Fe,Co)₃О₄-Based Alloys and their Magnetic Properties

Abstract

The structure of nanocrystalline Fe-Co-O alloys produced by high-energy ball milling and subsequent low-temperature annealing were investigated by X-ray diffraction analysis, scanning and transmission electron microscopy. The magnetic properties were measured in vibrating sample magnetometers at room temperature. The mixtures of FeO and Co powders were used as starting materials. The nanocrystalline composite alloys, obtained as a result of the milling, contained FeO and -Fe with the crystallite size of 12-18 nm as well as an amorphous phase. However, alloys subjected to subsequent annealing contained Fe3O4 and -Fe phases with crystallite size of 10-30 nm, in which Co is dissolved. Unlike the starting materials the produced powders exhibit properties typical of magnetically hard alloys. The intrinsic coercive force of the annealed powders increases with increasing (Fe,Co)3O4 phase content and reaches approximately 800 Oe.

Structure and Magnetic Properties of Hard Magnetic Nanocrystalline Oxide-Based Alloys

“…5). As an example, Figure 6 shows the dark-field image (taken in reflection of (FeCo) 3 O 4 phase) of FeO+20 % Co powder subjected to high-energy milling for 6 h and subsequent annealing at 250 о С for 8 h. It is seen that a particle 0.5-0.6 µm in size includes (Fe,Co) 3 O 4 nanocrystallites 10-30 nm in size It was found that the coercive force of Fe-Co-O alloys containing of about 80 vol % of the (FeCo)3O4 phase reaches µ 0 H ci ≈ 0.08 T [7].…”

“…Structure and properties of magnetite-based powders. Magnetic alloys based on the Fe 3 O 4 magnetite are of substantial interest [5][6][7]. It was shown that, in using the mechanochemical treatment of Fe 2 O 3 +Fe, Fe 2 O 3 +Fe+Co and FeO+Co mixtures and subsequent annealing of synthesized material, hardmagnetic powders can be prepared.…”

“…The error of the coercive force and magnetization measurements does not exceed 3%. Treatment conditions and measurement techniques are given in detail in [3][4][5][6][7].…”