Magnetocaloric Effect in Nanostructured $Pr_2Fe_{17}$ and $Nd_2Fe_{17}$ Synthesized by High-Energy Ball-Milling

Nanocrystalline $Pr_2Fe_{17}$ and $Nd_2Fe_{17}$ powders with rhombohedral $Th_2Zn_{17}$-type crystal structure and average particle sizes around 20 nm have been obtained by high-energy ball milling. While the bulk alloys show a well-defined and sharp drop in the low-field magnetization curve at the Curie temperature, $T_{C}$ = 285 K (Pr) and 335 K (Nd), the ball-milled samples exhibit a substantial broadening of the ferro-to-paramagnetic transition due to a considerable augmentation of the disordered inter-grain boundaries. The latter results in an increase of more than 25% in the values of the full width at half maximum of the temperature dependence of the magnetic entropy change maintaining almost unchanged the relative cooling power.