Magnetic ordering and crystal field effects in quasi-caged structure compound PrFe₂Al₈

The compound PrFe₂Al₈ possesses a three-dimensional network structure resulting from the packing of Al polyhedra centered at the transition metal element Fe and the rare earth Pr. Along the c-axis, Fe and Pr form chains which are separated from each other by the Al-network. In this paper, the magnetism and crystalline electric field effects in PrFe₂Al₈ are investigated through the analysis of magnetization and specific heat data. A magnetic phase transition in the Pr lattice is identified at TNPr≈4K in dc magnetization and ac susceptibility data. At 2 K, the magnetization isotherm presents a ferromagnetic saturation, however, failing to reach full spin-only ferromagnetic moment of Pr³⁺. Metamagnetic step-like low-field features are present in the magnetization curve at 2 K which is shown to shift upon field-cooling the material. Arrott plots centered around T^Pr_N display "S"-like features suggestive of an inhomogeneous magnetic state. The magnetic entropy, S_m, estimated from specific heat outputs a value of R ln(2) at T_N2 suggesting a doublet state for Pr³⁺. The magnetic specific heat is modeled by using a 9-level Schottky equation pertinent to the Pr³⁺ ion with J=4. Given the crystalline electric field situation of Pr³⁺, the inference of a doublet state from specific heat and consequent long-range magnetic order is an unexpected result.