Improving mechanical and magnetocaloric responses of amorphous melt-extracted Gd-based microwires via nanocrystallization

Abstract

We report on the structural, mechanical, and magnetocaloric properties of annealed melt-extracted Gd53Al24Co20Zr3 amorphous microwires of ∼70 μm diameter. During heat treatment small islands of nanocrystallities are generated and isolated in the amorphous region for the wires. The size of the nanocrystallities ranges from 5 nm to 10 nm. The observed lattice distortion from the nanocrystallities causes changes in the magnetic properties of the wires. The annealing temperature of 100 °C has the largest strength (1845 MPa) as compared to wires annealed at other temperatures. This is likely to trigger nanophase transformation in the amorphous region and these nanocrystals have been preserved through the increase of annealing temperature. The formulation of the nanocrystalline islands is also verified by the selected-area electron diffraction (SAED). The microwires exhibit a large and reversible magnetocaloric effect (MCE), with the maximum isothermal magnetic entropy change (−ΔSM) and refrigerant capacity (RC) values of 9.5 J/kg K and 689 J/kg respectively for the microwire annealed at 100 °C. This RC is about 35%, 67%, and 91% larger than those of bulk Gd53Al24Co20Zr3 (∼509 J/kg), Gd (∼410 J/kg), and Gd5Si2Ge1.9Fe0.1 (∼360 J/kg) regardless of their ordering temperatures. These results demonstrate the ability to tune the mechanical and magnetic properties of the microwires by thermal annealing.