Thermodynamic and transport studies of the ferromagnetic filled skutterudite compound PrFe₄As₁₂

A variety of thermodynamic and transport measurements were made on high-quality single crystals of the Pr-based filled skutterudite compound PrFe₄As₁₂. Abrupt features in magnetization, ac susceptibility, specific heat, resistivity, thermoelectric power, and ultrasonic velocity reveal the onset of long range ferromagnetic order below Θ_C=18 K. The low-temperature magnetic susceptibility is characterized by a Curie–Weiss law with an effective moment of 3.52μ_B/f.u. and a saturation magnetization of 2.3μ_B/f.u., which is consistent with a magnetic Γ₅ triplet ground state. A gaplike reduction of the large electronic specific heat coefficient of 340 mJ/mol K² and several other features point to a strongly correlated electron behavior that is likely coupled to a change in magnetic and/or structural order near T^∗≃12 K. Furthermore, this complex magnetic state is found to be strongly field dependent, as evidenced by a change in the easy axis at low fields and an additional contribution to thermal conductivity appearing only at high fields.