Confinement-modulated Phase Transition of Fe-Ni Melt in Carbon Nanotube

Abstract

Fe-Ni nanowires demonstrate exceptional ‌magnetic anisotropy‌ and ‌high saturation magnetization‌, making them promising candidates for ‌spintronic devices‌ and ‌high-density magnetic storage applications. Conventionally, these nanowires are synthesized through ‌encapsulation within carbon nanotubes (CNTs)‌, leveraging the CNTs' structural confinement to control growth morphology. However, the ‌phase transition dynamics‌ of Fe-Ni alloys under CNT confinement remain underexplored. Here, we present a ‌systematic investigation‌ of the phase transition characteristics of Fe-Ni melt‌. Our results reveal that the molten Fe-Ni alloy undergoes a ‌spontaneous liquid-to-solid transition‌, followed by the formation of ‌coaxial-helical nanowires whose morphology governed by the competitive growth of ‌common neighbor sub-clusters.The ‌solidified structure‌ of Fe-Ni melt is critically determined by three key parameters: ‌filling density‌, ‌CNT diameter‌, and ‌helicity‌ of the host carbon nanotubes. Our study presents a ‌comprehensive phase diagram‌ that systematically maps the structural evolution of Fe-Ni melt as a function of CNT inner diameter, revealing distinct spiral growth under confinement. Particularly, Fe-Ni nanowires demonstrate ‌remarkable electronic transport characteristics‌, positioning them as promising candidates for ‌next-generation spintronic devices. This study ‌elucidates‌ the ‌phase transition mechanisms‌ of Fe-Ni alloy melt under confinement conditions, establishing a ‌theoretical framework‌ for their ‌rational design‌ in spintronic nanodevices.