Lanthanum Dilution Effects on the Giant Magnetocaloric Gd5Si1.8Ge2.2 Compound.

A study on the fundamental properties of Gd5−xLaxSi1.8Ge2.2 pseudo‐binary compounds with x = 1, 2, 3, 4, and 5 is performed by means of X‐ray powder diffraction (XRD) and magnetic measurements. An evolution from a monoclinic (M) Gd5Si2Ge2‐type to a tetragonal (T) Zr5Si4‐type structure, with the addition of La, is observed, finding that the T phase is stable for x ≥ 2. A monotonic expansion of the unit cell volume with a rate of 28 Å3/La by increasing the content of the non‐magnetic La ions in the system influences significantly the overall magnetic behavior. For instance, TC decreases in a rate of dTC/dx = −47.8 K La−1; and a considerable hysteresis reduction is observed as a result of the change on the nature of the phase transition from a first to a second‐order one. Hence, these results reveal the impact of a non‐magnetic La substitution on both magnetic and crystallographic properties of this series. A study on the crystallographic, magnetic, and magnetocaloric properties of (Gd,La)5(Si,Ge)4 pseudo‐binary compounds is presented here. The change from a monoclinic to a tetragonal structure for La content higher than 20% is observed. There is a monotonic decrease in TC with a considerable hysteresis reduction and a change on the nature of the phase transition from a first to a second‐order one. [ABSTRACT FROM AUTHOR]