Magnetocaloric effect in GdGeSi compounds measured by the acoustic detection technique: Influence of composition and sample treatment

Abstract

In this paper we explore the acoustic detection method applied to the investigation of the magnetocaloric effect in Gd and Gd 5 ͑Ge 1−x Si x ͒ 4 compounds, in the temperature range from 230 to 360 K and for magnetic fields up to 20 kOe. Measurements were performed in as-cast materials, both for powder and pellet samples, and in tree samples with compositions around Gd 5 Ge 2 Si 2 that underwent different thermal treatments. Small differences were observed when comparing powder and pellet samples of Gd and Gd 5 ͑Ge 1−x Si x ͒ 4 compounds with 0.500Ͻ x Յ 1.00. For the alloys with composition around Gd 5 Ge 2 Si 2 , which exhibit giant magnetostriction and coexistence of distinct phases, expressive changes were observed when comparing powder and pellet samples. Based on these cases, it is easy to see that the acoustic method can distinguish a second-order phase transition from a first-order magnetic-crystallographic one, and that it presents good sensitivity to detect spurious material phase in small quantities.

Determination of the entropy change using the acoustic detection technique in the investigation of the magnetocaloric effect

“…The temperature was then changed by 4 K and the whole process was repeated. The results are similar to those comprehensively described in [12,13]. Now, reversible adiabatic curves in a T versus H diagram can be numerically constructed by starting at a given temperature and sweeping the magnetic field from zero using the slopes (∂T /∂H ) S calculated using equation (1).…”

“…[10,11]. More recently we used this technique to obtain an evaluation of the temperature change for Gd and for a compound of the Gd 5 Ge 2 Si 2 family induced by fields up to 50 kOe [12,13]. However, up to now there has been no attempt to obtain the entropy change using the magnetoacoustic and this is a particularly interesting technique compared with the traditional methods because it does not involve assumption of continuity of the thermodynamic functions and their derivatives.…”

Untitled

“…Mechanical processes, in order to get the proper form, such as wires, thin plates, spheres can cause changes in MCE properties, even in samples with the same composition but different form, as these are strictly related to the crystallographic structure. Although only small differences in MCE properties were observed between powder and pallet form samples because of changes related to their phase composition and magnetostriction effects [12].…”

The structural, magnetic and magnetocaloric properties of MnCrNiGeSi high-entropy alloy

“…In the literature, many alloys have been researched for magnetic cooling systems such as Gd-based [32], Heusler type [33], pnictides [34,35], and perovskites [36], etc. The usable magnetocaloric material should exhibit some critical parameters.…”