Magnetocaloric properties of melt-extracted Gd_87.5Co_12.5 crystalline/crystalline composite microwires

Gadolinium (Gd) is the benchmark magnetocaloric material, yet its performance requires optimization in terms of working temperature range, refrigeration capacity (RC) and heat exchange capacity. Here, we address this challenge through a synergistic strategy combining Co alloying (to create an in-situ dual-phase magnetocaloric system) and the melt-extraction technique (to directly shape the alloy into microwires). This approach fabricates Gd_87.5Co_12.5 (at.%) crystalline/ crystalline composite microwires. The resulting microstructure comprises a Gd-rich matrix embedded with a magnetocaloric Gd_3Co phase, both of which are crystalline. This dual-phase architecture yields a remarkable magnetic entropy change (-\Delta S_\rm m) profile, which delivers an ultra-broad effective temperature span (\delta T) of 218.5 K (defined between the outer half-maximum points of the dual-peak magnetic entropy change vs. temperature curve, 107.6-326.1 K) and a high RC of 658.7 J/kg under 5 T. To our knowledge, this work represents the first investigation of the magnetocaloric effect (MCE) in Gd-based crystalline/crystalline composite microwires. More importantly, it validates a dual-route design paradigm: phase-composition engineering for broadened \delta T and RC, coupled with morphology engineering via melt-extraction for enhanced heat exchange. This work establishes a new paradigm for designing next-generation magnetocaloric materials with integrated performance enhancements, particularly for efficient magnetic refrigeration in applications like gas liquefaction.