Growing ferromagnetic Fe-Ni alloy nanoparticles on nanodiamond nanotemplates: the role of sp2-type carbon in their development and in the appearance of a martensitic-type phase

Abstract

This work presents a novel hybrid nanostructured magnetic material consisting of ferromagnetic (FM) fcc Fe-Ni nanoparticles (NPs) grown on nanodiamond (ND) nanotemplates. The development of this hybrid magnetic nanomaterial is realized through the combination of wet chemistry and thermal annealing under vacuum. The characterization and study of the prepared samples, which were performed using a range of specialized experimental techniques, reveal that thermal annealing of the as-made hybrid precursor under a range of different conditions leads to the growth of fcc Fe-Ni alloy NPs at the surfaces of the ND nanotemplates. These alloy NPs have an average size of 10 nm, exhibit uniform distribution on the ND nanotemplates and have a predominant nickel content of approximately 64 at%. They demonstrate FM behavior throughout a temperature range from 2 K to 400 K, with maximum magnetization values ranging between 8.6 and 11.9 emu g−1 and coercivities ranging between 10 and 610 Oe. Moreover, 57Fe Mössbauer spectroscopy reveals that apart from the predominant fcc FM Fe-Ni phase, iron atoms also participate in the formation of a secondary martensitic-type Fe-Ni phase, the development of which is attributed to the partial diffusion of carbon atoms at interstitial sites within the Fe-Ni lattices during the alloy NP formation at elevated temperatures, as a consequence of the unique morphological properties of the ND growth matrices, which facilitate surface formation and reconstruction of sp2 nanostructures. Concurrently to their diffusion within the Fe-Ni NP lattice, the carbon atoms are also found to reconstruct layered graphitic-type nanostructures enveloping the metallic alloy NPs, but only where ND NPs are adjacent. These non-typical nanohybrid materials hold significant potential for use in applications related, but not limited to biomedicine, biopharmaceutics, catalysis, and other various contemporary technological fields.