Near-equiatomic, ordered iron-rhodium (FeRh) alloy is a fundamentally interesting material that may become useful in niche applications making use of its unique magneto-functional phenomena, for example, the giant inverse magnetocaloric effect near room temperature associated with sharp first-order magnetic phase transition. The nearly discontinuous antiferromagnetic-ferromagnetic phase transformation in bulk FeRh is well-known; however, the transition broadens considerably in fine particles and films with thickness less than 50 nm, precluding their potential applications. Here, we report an abrupt, bulk-like first-order magnetoelastic transformation in powders consisting of sub-micron particles of nearly equiatomic FeRh compound synthesized via solid-state mechanochemical co-reduction of FeF2 and RhCl3 and subsequent heat treatments. We demonstrate that annealing at temperatures ranging from 600 ̊C to 800 ̊C enables tailoring phase content, particle size, and magnetic properties of the powders. A maximum magnetic-field-induced entropy change of ~10 J/kg K at μ₀ΔH = 1 T has been achieved in powders annealed at 800 ̊C. The retention of extraordinary responsiveness in sub-micron particles of FeRh is likely to open doors for system component fabrication using additive manufacturing methods, along with new opportunities to employ FeRh in theranostics.

近等原子有序铁铑 (FeRh) 合金是一种从根本上令人感兴趣的材料，利用其独特的磁功能现象可能会在利基应用中变得有用，例如，在室温附近与尖锐的第一-相关的巨大逆磁热效应阶磁相变。块状 FeRh 中几乎不连续的反铁磁-铁磁相变是众所周知的。然而，在厚度小于 50 的细颗粒和薄膜中，过渡明显变宽 nm，排除了它们的潜在应用。在这里，我们报告了粉末中突然的、块状的一级磁弹性转变，该粉末由通过 FeF2 和 RhCl3 的固态机械化学共还原和随后的热处理合成的近等原子 FeRh 化合物的亚微米颗粒组成。我们证明，在 600 ̊C 到 800 ̊C 的温度范围内进行退火可以调整粉末的相含量、粒度和磁性。在μ ₀ ΔH = 1时，最大磁场引起的熵变化约为 10  J/kg K T 已在 800°C 退火的粉末中实现。FeRh 亚微米颗粒中保持非凡的响应性可能为使用增材制造方法制造系统组件打开大门，同时也为在治疗诊断学中使用 FeRh 提供了新的机会。