Umkehr effect in Hall voltage of polycrystalline bismuth

The Hall effect has been measured on an isotropic polycrystalline Bi sample, from 5 K up to room temperature. It appears that the Hall voltage exhibits a strong asymmetry under sign reversal of magnetic field. This peculiar effect becomes more pronounced as the temperature decreases. It is shown that this astonishing behavior, at first glance, can be ascribed to the "Umkehr" effect, previously predicted from a phenomenological point of view, for the off-diagonal components of the magnetoresistivity tensor, for (3) over barm crystallographic point group.