Tunable Magnetocaloric Effect in Ni-Mn-Ga Microwires

Area of Science:

• Materials Science
• Thermodynamics
• Nanotechnology

Background:

• Magnetic refrigeration offers energy-efficient, eco-friendly cooling but faces challenges: hysteresis, narrow working temperature intervals (WTI), and poor mechanical stability.
• Off-stoichiometric Ni-Mn-Ga Heusler alloys show potential for giant magnetocaloric effect (MCE) and adjustable transformation temperatures.

Purpose of the Study:

• To address limitations in magnetic refrigeration materials by developing Ni-Mn-Ga microwires.
• To investigate the impact of high specific surface area (SSA) on material properties and magnetocaloric performance.
• To achieve tunable magnetocaloric effects through composition control and gradient distribution.

Main Methods:

• Fabrication of Ni-Mn-Ga microwires (35-80 μm diameter) using a melt-extraction technique.
• Analysis of material properties, including specific surface area (SSA), hysteresis, and mechanical stability.
• Tuning of transformation temperatures and magnetocaloric effect via composition adjustment and gradient creation.

Main Results:

• Ni-Mn-Ga microwires exhibited negligible hysteresis and enhanced mechanical stability, attributed to high SSA.
• Tunable magnetocaloric effects were achieved by adjusting composition and creating gradient distributions.
• Demonstrated magnetic entropy change (ΔSm) of ~-18.5 J kg⁻¹ K⁻¹ and a WTI up to ~60 K.
• Achieved a net refrigeration capacity of ~240 J kg⁻¹ at 50 kOe.

Conclusions:

• Ni-Mn-Ga microwires present a promising material for overcoming key drawbacks in magnetic refrigeration.
• The high SSA in microwires is crucial for improved stability and tunable properties.
• The developed approach is scalable and applicable to other small-sized materials for advanced cooling technologies.