Crystal structure, magnetocaloric effect and magnetovolume anomalies in nanostructured Pr2Fe17

Abstract

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 10h, with almost unchanged values for both crystalline lattice parameters (Δa; Δc<0.05%) and vanishing mechanically induced microstrain (<0.1%). Although the mean crystalline size decreases down to 20±3nm, magnetovolume anomalies observed in pure Pr2Fe17 are still present with a significant volume decrease on heating from 5 up to 320K. 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, |ΔSM|, decreases from 6.3 to 4.5J kg−1K−1 under an applied magnetic field μ0H=5T after the milling process. However, the width of the |ΔSM|(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.