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 x2. A monotonic expansion of the unit cell volume with a rate of 28 angstrom(3)/La by increasing the content of the non-magnetic La ions in the system influences significantly the overall magnetic behavior. For instance, T-C decreases in a rate of dT(C)/dx=-47.8KLa(-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.



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Andrade, VM; Belo, JH; Reis, MS; Costa, RM; Pereira, AM; Araujo, JP

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VMA thanks the CNPq for the Grant No. 203180/2014-3. MSR acknowledges FAPERJ, CAPES and CNPq (Brazil) for funding the research projects. JHB thanks FCT for the grant SFRH/BD/88440/2012 and the project PTDC/CTMNAN/115125/2009. MSR belongs to the INCT of Refrigeracao e Termofisica, funded by CNPq by the grant number 465448/2014-3. This work was also funded by FEDER funds through the COMPETE 2020 Programme and National Funds throught FCT - Portuguese Foundation for Science and Technology under the projects UID/CTM/50025/2013 and UID/NAN/50024/2013 and by NECL with the project NORTE-01-0145-FEDER-022096.

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