Hidden constant in the anomalous Hall effect of high-purity magnet MnSi

Measurements of the Hall conductivity in MnSi can provide incisive tests of theories of the anomalous Hall (AH) effect, because both the mean free path and magnetoresistance (MR) are unusually large for a ferromagnet. The large MR provides an accurate way to separate the AH conductivity ₗₘ^A from the ordinary Hall conductivity ₗₘ^N. Below the Curie temperature T₂, ₗₘ^A is linearly proportional to M (magnetization) with a proportionality constant S₇ that is independent of both T and H. In particular, S₇ remains a constant while ₗₘ^N changes by a factor of 100 between 50. 3em{0ex}K and T₂. We discuss implications of the hidden constancy in S₇.