Colloids of HEA Nanoparticles in an Imidazolium-Based Ionic Liquid Prepared by Magnetron Sputtering: Structural and Magnetic Properties

Colloids consisting of the CoCrCuFeNi high-entropy alloy nanoparticles in ionic liquid with the 1-butyl-3-methylimidazolium ([BMIM]+) cation and the tetrafluorborate ([BF4]-) anion were obtained by the DC magnetron sputtering of high-entropy alloy target in vacuum, onto the surface of [BMIM.BF4] ionic liquid. The method of the nanoparticle colloid preparation is based on negligibly small vapour pressure of the ionic liquid, which allows its application in vacuum. The high-entropy alloy nanoparticle colloids were studied by HRTEM microscopy and SQUID magnetometry. Results of the structural and magnetic analyses show that the colloids contain ultra-small single-crystalline nanoparticles of an uneven shape and typical size of (2−3) nm. The nanoparticles have relatively narrow size distribution which is typical for this preparation method. The high-entropy alloy nanocolloids show complex magnetic properties that are a function of temperature, applied magnetic field and mass content of the nanoparticles in the colloids. The obtained results imply significant magnetic interactions between the ionic liquid and the high-entropy alloy nanoparticles