Crystal structure, magnetocaloric effect and magnetovolume anomalies in nanostructured Pr2Fe17

Using high-energy ball milling, nanostructured Pr2Fe17 powders can be obtained from their arc-melted bulk alloys. High-resolution X-ray and neutron powder diffraction experiments reveal that the Th2Zn17-type rhombohedral crystal structure is maintained, after milling for 10 h, with almost unchanged values for both crystalline lattice parameters (Delta a; Delta c < 0.05%) and vanishing mechanically induced microstrain (< 0.1%). Although the mean crystalline size decreases down on 20 +/- 3 nm, magnetovolume anomalies observed in pure Pr2Fe17 are still present with a significant volume decrease on heating front 5 up to 320 K. After the milling, a significant increase in the magnetic anisotropy, due to the drastic reduction in crystalline size, is observed, while the value of the magnetic moment seems to be increased slightly (5%). In addition, the magnetocaloric effect of bulk and nanostructured Pr2Fe17 has been investigated. The magnetic entropy change, |Delta S-M|, decreases from 6.3 to 4.5 J kg(-1) K-1 under an applied magnetic field mu H-0 = 5 T after the milling process. However, the width of the |Delta S-M|(T) curve is substantially enlarged and hence the refrigerant capacity is enhanced. These findings make the iron-based nanostructured Pr2Fe17 powders interesting for applications in magnetic refrigeration at around room temperature. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.