Giant magnetocaloric effect in Gd5(Si2Ge2) alloy with low purity Gd

Abstract

Gd5(Ge1-xSi x), x < 4 based alloys are potential candidates for magnetic refrigeration in the range ~20 - ~290 K. However, one of the greatest obstacles for the use of that technology in large scale is the utilization of high pure Gd metal (99.99 wt. (%)) to produce the GdGeSi alloys, since the impurity elements decrease the intensity of the magnetocaloric effect (EMC)¹. In this work, we prove that annealing of the Gd5Ge2Si2 can promote remarkable values for the EMC in comparison to those obtained for the alloy with high pure Gd. Also, the as cast alloy and the annealed alloy are not monophasic, but have at least two crystalline phases in their microstructure. Results for X-ray analysis, optical and electronic microscopy and magnetization measurements are reported

R5T4 Compounds

“…Essentially, the authors studied the composition range between Gd 5 (Si 0.5 Ge 0.5 ) 3 and Gd 1 (Si 0.5 Ge 0.5 ) 1 phases, and expectedly found that the alloy with x ¼ 0.45 (closest to the Gd 5 (Si 0.5 Ge 0.5 ) 4 composition) shows the largest MCE. Alves et al (2004) were able to obtain GMCE (19 J/Kg K for DH ¼ 70 kOe at T C ¼ 274 K) in Gd 5 Si 2 Ge 2 alloy prepared from low-purity Gd by using the high-temperature heat treatment of the cast alloy at 1650 C for 48 h. However, a significant amount of the O(I) structure magnetically ordering at 299 K through a second-order transition was still present in the sample after annealing. 0.45) contain the monoclinic 5:4 phase, but Gd-depleted samples contain the orthorhombic O(I) 5:4 phase.…”

Unusual effects of manual grinding and subsequent annealing process observed in Gd5.09Ge2.03Si1.88 compound

“…3, but using commercial (low purity) gadolinium, we do not obtain the same results. Our as-prepared Gd5Ge2Si2 compound presents only the second-order transition at 300 K, such as has been reported for other commercial-purity-Gd-as-cast samples of Gd5Ge2Si2 [4,5]. To obtain the first-order transition, the one of lowest temperature, it is necessary to carry out heat treatments [4].…”

The effect of low temperature annealing on the structure of Gd5Si2Ge2 alloy

“…The same reason is used to explain the rising of the magnetic entropy change in the low purity Gd 5 Si 2 Ge 2 alloy after annealing in Ref. [10]. If the irreversible ␤-␥ transition occurred in these alloys, some Gd 5 Si 4 -type phases can be obtained and the magnetic entropy changes will not be so high.…”