Structure and Magnetic Properties of FeRh Microflakes

This work reports the development of a thermoresponsive composite material based on poly(N-isopropylacrylamide) (PNIPAM) and FeRh alloy microflakes for biomedical applications. PNIPAM is a polymer exhibiting a sharp, reversible phase transition at its lower critical solution temperature (LCST) near physiological conditions, making it attractive for smart coatings and drug delivery. FeRh alloy undergoes a first-order antiferromagnetic–ferromagnetic (AFM-FM) transition with a pronounced magnetocaloric effect (MCE), enabling magnetic field–induced thermal control. The study was conducted within a project on the impact of particle size reduction on the AFM–FM transition and MCE. It was shown that FeRh flakes of ~200 μm in diameter and ~1 μm in thickness retain a transition temperature comparable to the bulk alloy, and a simple hand-filing method provides an effective route to obtain such structures. Microflakes were characterized by SEM, XRD, and Magnetic Properties Measurement System, while PNIPAM was grafted onto their surface via a “grafting-to” approach. Atomic force microscopy confirmed successful functionalization. The resulting FeRh–PNIPAM composites combine thermal and magnetic responsiveness, offering a promising platform for smart implants, controlled drug delivery, and adaptive biomedical coatings.