Magnetic and Transport Anomalies and Large Magnetocaloric Effect in Cubic R4PtAl (R = Ho and Er)

We report the electronic properties of R4PtAl (R = Ho, and Er), which contains three sites for R, by the measurements of magnetization (ac and dc), heat-capacity, transport, and magnetoresistance (MR). Dc magnetization data reveal antiferromagnetic order below 19 K and 12 K in Ho and Er compounds, respectively. Additional features observed at lower temperatures (12 K for Ho4PtAl and 5 K for Er4PtAl) are akin to the cluster spin-glass phase. Resistivity data exhibit a weak minimum at a temperature marginally higher than their respective Néel temperature (TN), which is unusual for such rare-earths with well-localized 4f states. Isothermal magnetization and magnetoresistance data well below TN exhibit signatures of a subtle field-induced magnetic transition for a small magnetic field (<10 kOe). Notably, the isothermal entropy change at TN has the largest peak value within this rare-earth family; for a field change from zero to 50 kOe, the entropy change is ~14.5 J/kg K (Ho4PtAl) and ~21.5 J/kg K (Er4PtAl) suggesting a role of anisotropy of 4f orbital in determining this large value. The results provide some clues for the advancement of the field of magnetocaloric effect. The magnetocaloric property of Er4PtAl is nonhysteretic, meeting a challenge to find materials with reversible magnetocaloric effect.