Itinerant-Electron Weak Ferromagnetism in La-Based Filled Skutterudite LaFe₄As₁₂

Abstract

High-quality samples of LaFe 4 As 12 with a residual resistivity ratio of 64 have been successfully synthesized under high pressure ∼4 GPa at 1100 K. The magnetization, specific heat, electrical resistivity, and Hall coefficient of the samples were measured. All the investigated properties exhibit evident anomalies at 5.2 K, thereby indicating a ferromagnetic transition. The large Rhodes–Wohlfarth ratio (≡ the ratio of the effective moment deduced from the Curie constant to the saturation moment per magnetic ion) of 32 suggests that LaFe 4 As 12 is the first La-based filled skutterudite that exhibits itinerant-electron weak ferromagnetism, which is realized by the high density of states at the Fermi level D ( E F ). The ferromagnetism is unexpected within the simple Stoner-type argument, because D ( E F ) lies between those of an ordinary Pauli paramagnet LaFe 4 P 12 and an enhanced Pauli paramagnet LaFe 4 Sb 12 in the LaFe 4 X 12 (X = P, As, Sb) series. We discuss this unexpected ferromagnetic transition on the basis of the difference in the spin-fluctuation strength between As- and Sb-based systems.