  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 (< 2.5h), a reduction of the
Gd5Si1.3Ge2.7 and Tb5Si2Ge2 particles size was achieved down to approximately
3.5 DSm. 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 minutes 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.
