Cryogenic Laser Synthesis of FeNiN Nanoparticles for Magnetic Hyperthermia Applications

The synthesis of iron−nickel nitride (FeNiN) nanoparticles by pulsed laser irradiation of commercial iron−nickel alloy powder dispersed in liquid nitrogen is described, along with its application in magnetic hyperthermia. Sustainable and efficient production generates FeNiN nanoparticles with a circular geometry having an average diameter between 6 nm and 9 nm. The fragmentation process of pure FeNi particles in a strictly nitrogenous environment facilitates the incorporation of interstitial nitrogen atoms, promoting the direct formation of crystalline FeNiN nanoparticles, regardless of the laser wavelength used, whether infrared (1064 nm), visible (532 nm), or ultraviolet (355 nm). High-resolution electron microscopy analyses, along with chemical imaging and electron diffraction, demonstrate the high mass conversion efficiency of FeNi into chemically ordered crystalline FeNiN nanoparticles in the L10 phase. Oscillating magnetic fields with intensities of 1920 Am−1, 2560 Am−1, and 3200 Am−1 at frequencies of 100 kHz provide significant self-heating of FeNiN nanoparticles in water, with concentrations determined by absorbance measurements. A specific absorption ratio of 5.23 W/g, mainly due to the Néel relaxation mechanisms determined by particle sizes smaller than the critical size for the formation of magnetic multidomains, is highly promising for magnetic hyperthermia applications.