Near room-temperature magnetocaloric properties of Gd–Ga alloys

Abstract

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 20at%) 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 ~50–100µm), the melt-spun alloys have nanostructured (~50–100nm) 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—~0.5K per at% of Ga, and the as-cast alloys (5≤x≤20) have similar TC (~286K). The saturation magnetization (MS) derived from M–H curves (260K), show that alloying of Ga with Gd decreases MS. MS for melt-spun alloys decreases from ~108emu/g for Gd to ~42emu/g for Gd80Ga20 and for as-cast alloys MS decreases from ~120emu/g for Gd to ~62emu/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—~433J/kg for Gd to ~235J/kg for Gd80Ga20 for melt spun alloys and ~462J/kg for Gd to ~306J/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.