Magnetic properties and magnetocaloric effects in RPdAl (R=Gd-Er)

In this article, the investigation progress is reviewed in magnetic field and temperature dependences of the magnetic properties and magnetocaloric effects (MCEs) for RPdAl compounds with the orthorhombic TiNiSi-type (LTM) and the hexagonal ZrNiAl-type (HTM) structures. The LTM-RPdAl (R=Gd, Tb, Dy, Ho and Er) compounds are found to be antiferromagnet with the Néel temperature T_N=31, 45, 21, 10 and 10 K, respectively. It has been confirmed that the HTM-RPdAl (R=Tb, Ho and Er) compounds undergo the antiferromagnetic (AFM)-to-paramagnetic (PM) transition at T_N=43, 12 and 5 K, while the HTM-RPdAl (R=Gd and Dy) compounds undergo the ferromagnetic (FM)-to-PM transition at their respective Curie temperature, which is T_C =49 K and 25 K, respectively. A field-induced metamagnetic transition from AFM to FM state is observed below T_N in the antiferromagnetic RPdAl. For the HTM-RPdAl (R=Ho and Er) compounds, a small magnetic field can induce an FM-like state due to a weak AFM coupling, which leads to a high saturation magnetization, and gives rise to a large MCE around T_N. The maximum value of magnetic entropy change (ΔS_M) reaches -20.6 and -24.3 J/kg·K with a refrigerant capacity (RC) value of 386 and 299 J/kg around T_N for a field change of 0~5 T, respectively. The large ΔS_M and considerable RC suggest that HTM-RPdAl may be an appropriate candidate for magnetic refrigerant in low temperature ranges.