Near room-temperature magnetocaloric properties of Gd–Ga alloys

• The magnetocaloric properties of as-cast and melt-spun Gd–Ga alloys were examined.
• As-cast and melt-spun alloys were microstructured and nanostructured respectively.
• Curie temperature and saturation magnetization decreases upon alloying Gd with Ga.
• Maximum magnetic entropy change and refrigerant capacity decrease with Ga addition.
• The magnetocaloric properties were superior to Gd–B and Gd–In alloys.

The magnetocaloric properties of Gd–Ga alloys were examined with the aim to explore their potential application as magnetic refrigerants near room-temperature. A series of Gd100−xGax (x=0, 5, 10, 15, and 20 at%) alloys were prepared by conventional melting and rapid solidification. Both as-cast and melt-spun alloys are comprised of α-Gd and Gd5Ga3 with differing microstructural characteristics. While the as-cast alloys have proeutectic α-Ga and eutectic α-Ga+Gd5Ga3 (grain size ~50–100 µm), the melt-spun alloys have nanostructured (~50–100 nm) α-Ga and Gd5Ga3. The Curie temperature (TC) derived from M–T curves indicates that alloying of Ga with Gd decreases TC. The decrease in TC for melt-spun alloys is gradual—~0.5 K per at% of Ga, and the as-cast alloys (5≤x≤20) have similar TC (~286 K). The saturation magnetization (MS) derived from M–H curves (260 K), show that alloying of Ga with Gd decreases MS. MS for melt-spun alloys decreases from ~108 emu/g for Gd to ~42 emu/g for Gd80Ga20 and for as-cast alloys MS decreases from ~120 emu/g for Gd to ~62 emu/g for Gd80Ga20. Both maximum magnetic entropy change (−ΔSM)max and refrigerant capacity (RC) for as-cast and melt-spun alloys are lower than Gd. (−ΔSM)max decreases by ~1.55% and ~3.0% per atomic percent of Ga in as-cast and melt-spun alloys, respectively. A steeper decrease in RC is observed in melt-spun alloys than is observed for as-cast alloys—~433 J/kg for Gd to ~235 J/kg for Gd80Ga20 for melt spun alloys and ~462 J/kg for Gd to ~306 J/kg for Gd80Ga20 for as-cast. As-cast alloys appear to have better magnetocaloric properties than the melt-spun alloys. Alloying of diamagnetic Ga with Gd provides superior magnetocaloric properties compared to other diamagnetic elements in Group 13. The near room-temperature magnetocaloric properties of Gd–Ga alloys were comparable to a few first-order-transition based magnetic refrigerants.