Influence of short time milling in R5(Si,Ge)4, R = Gd and Tb, magnetocaloric materials

• Gd5Si1.3Ge2.7, the ball milling process promotes a 2nd order phase transition due strain induced.
• A decrease in 35% of the MCE (remaining with structural transition) for Gd5Si1.3Ge2.7
• For Tb5Si2Ge2 this strain promote stronger coupling of the structural and magnetic transition.
• In Tb5Si2Ge2 the ball milling increases up to 23% the MCE.

The effect of the short milling times on R5(Si,Ge)4 R = Gd, Tb magnetocaloric material properties was investigated. In particular, the effect of milling on atomic structure, particles size and morphology, magnetic, and magnetocaloric effect was studied. With short milling times (< 2.5 h), a reduction of the Gd5Si1.3Ge2.7 and Tb5Si2Ge2 particles size was achieved down to approximately 3.5 μm. For both compositions the main differences are a consequence of the milling effect on the coupling of the structural and magnetic transitions. In the Gd5Si1.3Ge2.7 case, a second-order phase transition emerges at high temperatures as a result of ball milling. Consequently, there is a decrease in the magnetocaloric effect of 35% after 150 min of milling. Interestingly, an opposite effect is observed in Tb5Si2Ge2 where a 23% increase of the magnetocaloric effect was achieved, driven by the enhancement of the coupling between magnetic and structural transitions arising from internal strain promoted by the milling process.

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