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 σxyA from the ordinary Hall conductivity σxyN. Below the Curie temperature TC, σxyA is linearly proportional to M (magnetization) with a proportionality constant SH that is independent of both T and H. In particular, SH remains a constant while σxyN changes by a factor of 100 between 50.3em0exK and TC. We discuss implications of the hidden constancy in SH.