Gd5(Si,Ge)4 thin film displaying large magnetocaloric and strain effects due to magnetostructural transition

Abstract

Magnetic refrigeration based on the magnetocaloric effect is one of the best alternatives to compete with vapor-compression technology. Despite being already in its technology transfer stage, there is still room for optimization, namely, on the magnetic responses of the magnetocaloric material. In parallel, the demand for different magnetostrictive materials has been greatly enhanced due to the wide and innovative range of technologies that emerged in the last years (from structural evaluation to straintronics fields). In particular, the Gd5(SixGe1−x)4 compounds are a family of well-known alloys that present both giant magnetocaloric and colossal magnetostriction effects. Despite their remarkable properties, very few reports have been dedicated to the nanostructuring of these materials: here, we report a ∼800 nm Gd5Si2.7Ge1.3 thin film. The magnetic and structural investigation revealed that the film undergoes a first order magnetostructural transition and as a consequence exhibits large magnetocaloric effect (−ΔSmMAX ∼ 8.83 J kg−1 K−1, ΔH = 5T) and giant thermal expansion (12000 p.p.m). The thin film presents a broader magnetic response in comparison with the bulk compound, which results in a beneficial magnetic hysteresis reduction. The ΔSmMAX exhibited by the Gd5(Si,Ge)4 thin film makes it a promising candidate for micro/nano magnetic refrigeration area.

Field-temperature phase diagrams of freestanding and substrate-constrained epitaxial Ni-Mn-Ga-Co films for magnetocaloric applications

“…9 Thin films have been proposed to overcome this issue due to their high surface-to-volume ratio, which allows for a fast heat exchange. 10 There is some literature on magnetocaloric films for both Heusler- [11][12][13][14] and rare-earthbased 15,16 materials and other compounds, 17 but this work is limited to films on substrates. However, the huge heat capacity of the substrate compared to a thin magnetocaloric film results in a vanishing usable temperature change.…”

Contributions to Hysteresis in Magnetocaloric Materials

“…In recent times there has been a concerted effort to study epitaxial thin films as an alternative to single crystals. There is a considerable literature on thin film Heusler alloys and reports of Gd 5 Si 2 Ge 2 MCE thin films although reports of La(FeSi) 13 thin films showing first order character at the transition, are still lacking. As many material families have large magnetovolume coupling, they are sensitive to strain (and show large changes of entropy under hydrostatic pressure).…”

Annealing influence on the magnetostructural transition in Gd5Si1.3Ge2.7 thin films

“…The preparation details of Gd5Si1.3Ge2.7 thin films (~780 ± 25 nm thick) on SiO2-covered Si substrates using femtosecond pulsed laser deposition and single crystal target were described in Ref [2]. In order to study the effects of different annealing temperatures, the samples were wrapped in a tantalum sheet, placed into a crucible, and introduced in a quartz tube with a zirconium getter to prevent oxidation.…”

“…The recent success in the production of Gd5(SiXGe1-x)4 thin films using femtosecond pulsed laser deposition opened new prospects for the optimization of the production process, with the aim of increasing the giant magnetocaloric effect (GMCE) in these nanomaterials [1,2]. It is well known that thin film properties are very sensitive to thickness, substrate type, oxygen content, as well as deposition and annealing parameters etc.…”