Anomalous Hall effect in three ferromagnetic compounds: Eu Fe4 Sb12, Yb14 Mn Sb11, and Eu8 Ga16 Ge30

The Hall resistivity (ρxy), resistivity (ρxx), and magnetization of three metallic ferromagnets are investigated as a function of magnetic field and temperature. The three ferromagnets, Eu Fe4 Sb12 (Tc 84 K), Yb14 Mn Sb11 (Tc 53 K), and Eu8 Ga16 Ge30 (Tc 36 K) are Zintl compounds with carrier concentrations between 1× 1021 and 3.5× 1021 cm-3. The relative decrease in ρxx below Tc [ρxx (Tc) ρxx (2 K)] is 28, 6.5, and 1.3 for Eu Fe4 Sb12, Yb14 Mn Sb11, and Eu8 Ga16 Ge30, respectively. The low carrier concentrations coupled with low magnetic anisotropies allow a relatively clean separation between the anomalous (ρ xy ′), and normal contributions to the measured Hall resistivity. For each compound the anomalous contribution in the zero field limit is fit to a ρxx + σxy ρ xx 2 for temperatures T< Tc. At T=0 the anomalous Hall conductivity σ xy 0, is -220±5 (Ω-1 cm-1), -14.7±1 (Ω-1 cm-1), and 28±3 (Ω-1 cm-1) for Eu Fe4 Sb12, Yb14 Mn Sb11, and Eu8 Ga16 Ge30, respectively, and is independent of temperature for T< Tc if the change in spontaneous magnetization (order parameter) with temperature is taken into account. These data are consistent with recent theories of the anomalous Hall effect that suggest that even for stochiometric ferromagnetic crystals, such as those studied in this article, the intrinsic Hall conductivity is finite at T=0, and is a ground state property that can be calculated from the electronic structure.