Phase transition and magnetocaloric effect in particulate Fe-Rh alloys

Micro-sized particles of Fe_xRh_100−x (x = 50, 48, 45, 40, and 35) binary alloys were synthesized by a solid-phase reduction method and their structural properties, magnetic properties and cytotoxicity have been characterized. From X-ray diffraction results, the Fe₅₀Rh₅₀ alloy is in a single chemically ordered α′ phase while the face-centered cubic disordered γ phase arises and increases with Rh content when x is smaller than 50. The magnetization behavior of the alloys demonstrates that the α′ phase consists of ferromagnetic and antiferromagnetic components due to the nonuniformity of elements in the particulate alloys. The maximal magnetic entropy change and the relative refrigeration capacity of the Fe₅₀Rh₅₀ particles reach 9.7 J/kg K and 230 J/kg, respectively, with a 0–3 T magnetic field change. Despite its moderate magnetic entropy among the first-order transition materials, Fe₅₀Rh₅₀ microparticles are promising for biomedical applications due to its large relative cooling power and low cytotoxicity.