59Co NMR study in Co–Fe alloys/Co magnetite composites

• Published in: Solid state sciences Vol. 3; no. 3; pp. 301 - 308
• Main Authors: Jay, Jean Philippe, Jurca, Ioan-Sorin, Pourroy, Geneviève, Viart, Nathalie, Mény, Christian, Panissod, Pierre
• Format: Journal Article
• Language: English
• Published: Paris Elsevier Masson SAS 01-03-2001; Elsevier
• Subjects: Alloys; Applied sciences; Composite; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; FeCo alloys; Isomorphous to α-Mn; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Metals. Metallurgy; NMR spectroscopy; Nuclear magnetic resonance and relaxation; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Composite; NMR spectroscopy; FeCo alloys; Isomorphous to α-Mn; Inorganic compounds; Oxides; Cobalt 59; Iron alloys; Experimental study; Cobalt; Cobalt base alloys; Binary alloys; Composite materials; Transition elements; NMR spectra; Iron oxides; Transition element alloys; Crystal structure
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/S1293-2558(00)01100-6

Iron–cobalt compounds containing 20–30 at.% Fe with unusual crystallographic structure have been observed in metal-oxide composite synthesized in an aqueous media at 120–140°C. The oxide is a cobalt-containing magnetite. The metallic component is found in two crystallographic structures depending on the preparation conditions: a b.c.c. (α-Fe) structure and an α-Mn, also called Re
24Ti
5, structure (space group
I-43
m). The α-Mn-like CoFe alloy is encountered for the first time and transforms into the b.c.c. structure during annealing at temperatures as low as 160°C. In the b.c.c. structure itself, the cobalt and iron atoms present a chemical short-range order totally different from the regular B2 phase of the ordered bulk CoFe compound. This particular order is similar to the one encountered in high vacuum co-deposited thin films. For annealing temperatures larger than 400°C, the metallic component loses some Fe and transforms into nearly pure f.c.c. cobalt. This study shows that chemical as well as physical low temperature preparation techniques favor original CoFe ordered phases not achievable by conventional metallurgy.