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Micro-sized particles of FexRh100−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. [ABSTRACT FROM AUTHOR]

Materials exhibiting a large magnetocaloric effect (MCE) at or near room temperature are critical for solid-state refrigeration applications. The MCE is described by a change in entropy (ΔSM) and/or temperature (ΔTad) of a material in response to a change in applied magnetic field. Ball milled materials generally exhibit smaller ΔSM values compared to bulk; however, milling broadens the effect, potentially increasing the relative cooling power (RCP). The as-cast Gd5Si4 is an attractive option due to its magnetic transition at 340 K and associated MCE. Investigation of effect of particles size and transition temperature in the binary material, Gd5Si4, can lead to development of functionally graded bulk material with higher MCE and RCP than the traditional bulk materials. A two-step ball-milling process, in which coarse powder of Gd5Si4 was first milled with poly(ethylene glycol) followed by milling in heptane was used to produce fine particles of Gd5Si4 that showed a broad distribution in particle size. Magnetic measurement on the milled sample obtained after washing with water show a decrease in Curie temperature and significant broadening of the magnetic transition. Compared to bulk Gd5Si4, the maximum MCE of the milled samples is also reduced and shifted down by close to 30 K, but the MCE remains substantial over a broader temperature range. The RCP of both milled samples increased 75% from the bulk material. [ABSTRACT FROM AUTHOR]