Magnetic and microwave properties of Fe18Ni82 nanoparticles with close to zero magnetostriction

Abstract

Magnetic nanoparticles (MNPs) with nominal Fe18Ni82 composition were prepared by the electrophysical technique of the electrical explosion of wire. Although we were not able to experimentally estimate the magnetostriction coefficient for MNPs, this iron–nickel ratio is usually associated to close to zero magnetostriction. Different values of the overheating rate K between 0.9 and 2.0, where K is the ratio between the electrical energy ejected into the wire and the sublimation energy of Fe18Ni82 alloy, were used for the fabrication of the MNPs. Structural characterization (X-ray diffraction, scanning electron microscopy, low temperature nitrogen adsorption), magnetic and microwave measurements were used for the comparative analysis of the properties of MNPs. The increase of the overheating rate led to the increase of the specific surface value (Ssp) of the MNPs and the decrease of their average size. The fabricated MNPs were spherical in shape with a very high degree of sphericity and very weakly aggregated with the average weighted diameter in the range of 94–301 nm depending on the specific surface value for each batch. For 0.9 ≤ K ≤ 1.2 the MNPs were in the γ-phase, cubic (S.G: Fm-3 m) face-centered cubic lattice and very a small amount of material had a cubic Pm-3 m structure with lost symmetry. For 1.2 < K ≤ 2.0 they were single γ-phase, cubic (S.G: Fm-3 m) face cubic centered structure. Magnetic measurements and microwave absorption showed that the MNPs of all batches have high saturation magnetization and exhibit both microwave phenomena: significant zero field microwave absorption and resonant absorption in the vicinity of the ferromagnetic resonance field. Contrary to previous studies of FeNi MNPs with non-zero magnetostriction, the field for ferromagnetic resonance was very close to the one expected for MNPs with small contributions arising from magnetocrystalline anisotropy, strains and the deviations from sphericity. The magnetic and microwave characteristics in combination with a very high value of the single batch are promising for technological applications of these MNPs including the development of composites consisting of a polymer matrix filled with MNPs.