The structure, magnetic and magnetocaloric effect of misch-metal (MM)2Fe17-xAlx (x=0-2) compounds

Abstract In this study, the structural, magnetic and magnetocaloric effects (MCE) of misch-metal MM2Fe17−xAlx (0 ≤ x ≤ 2) compounds are investigated. The XRD patterns indicate that all the samples crystallize primarily in a rhombohedral Th2Zn17 type crystal structure coexisting with a small amount of precipitation phase α-Fe. The lattice parameters and the Curie temperature (TC) increase linearly with the increase of Al content. This allows the MM2Fe17−xAlx compounds to achieve magnetic refrigeration over the entire room temperature range. The maximum values of entropy changes (ΔSM) for MM2Fe17−xAlx (x = 0, 0.5, 1 and 1.5) compounds with a magnetic field variation of 0–2 T and 0–5 T are determined to be −2.1 J Kg-1 K−1, −1.3 J Kg-1 K−1, −1.9 J Kg-1 K−1, 1.9 J Kg-1 K−1 and −4.0 J Kg-1 K−1, −2.7 J Kg-1 K−1, −3.5 J Kg-1 K−1, −3.5 J Kg-1 K−1, respectively. The relative cooling power (RCP) for all the studied compounds is larger than 90 and 270 Jkg−1 while the full-width half maxima (δTFWHM) is larger than 60 K and 100 K with the field changes of 0–2 T and 0–5 T, respectively. These results indicate that MM2Fe17−xAlx (0 ≤ x ≤ 2) compounds could have higher magnetocaloric cost-performance comparable to the room-temperature magnetic refrigeration materials R2Fe17 (R = Pr, Nd) and Gd with the second-order phase transition (SOPT).