Laser irradiation of iron, cobalt, and nickel targets in liquid nitrogen: A facile approach for nitride nanoparticle fabrication of ferromagnetic transition metals

Nitride nanoparticles of ferromagnetic metal elements were produced by laser irradiation from metallic targets immersed in liquid nitrogen using Nd:YAG lasers with wavelengths of 532 and 1024 nm. Transmission electron microscopy analyses of the precipitated nanoparticles from the suspensions on microscopy grids reveal agglomerates consisting of polydisperse particles with sizes in the tens of nanometers range. Some particles with size of several hundreds of nanometers indicate that laser irradiation promotes cryoablation together with plasma erosion of the targets. Selected area electron diffraction analyses corroborated by Raman measurements indicate the formation of crystalline metal nitrides with spheroidal and acicular morphologies. Regardless of the laser radiation wavelength, nanoparticles with similar nitride phases are found: Fe4N and Fe16N2 for Fe target, Co2N and Co3N for Co target, Ni4N with Ni8N for Ni target. All nanoparticles show superparamagnetic-like behavior with a blocking temperature varying significantly with the nanoparticle size. Such single-step method is a promising green route for nanoparticle production of these metal nitrides, which are commonly obtained using more complex and multi-step processes. (C) 2017 Elsevier B.V. All rights reserved.