Control of particle size via chemical composition: Structural and magnetic characterization of Ni–Co alloy nanoparticles encapsulated in lamellar mixed oxides

Nanoparticles of Co–Ni alloys were prepared by thermal decomposition of layered double hydroxides (LDH) containing co-intercalated complexes of two metals. The precursor compounds [LiAl2(OH)6]2{Ni1−xCox(EDTA)} · 4H2O (where EDTA is ethylenediaminetetraacetate) obtained by anion exchange from [LiAl2(OH)6]Cl · 1.5H2O were treated at 450 °C in vacuum. The microstructure of the thermal products was studied using local (TEM, SAED, EDX) as well as integral (XRD, SAXS) methods. It was found that Ni–Co alloy nanoparticles are formed uniformly dispersed in the carbonized matrix of lamellar mixed oxides, and the increase of the relative cobalt content in Ni1−xCox from x = 0 to 0.86 leads to gradual enlargement of the average alloy particle size from 9 to 16 nm. According to magnetic measurements by SQUID magnetometry and FMR, all alloys, except Ni0.14Co0.86, are superparamagnetic at room temperature. The results on particle size obtained by different techniques are in good agreement. The variation of nanoparticle size via chemical composition in alloys and the use of LDH intercalation matrices is a promising way to synthesize nanocomposites with target properties.