Measurements of the Hall Effect and Resistivity in Pyrrhotite

Abstract

Hall-effect and resistivity experiments were carried out on natural crystals of pyrrhotite, in the temperature range from 77 to 450\ifmmode^\circ\else\textdegree\fi{}K. Because of the magnetic anisotropy, samples were cut and measured in three different orientations of the hexagonal crystals. For samples cut with their long axis perpendicular to the $c$ axis and with the magnetic field applied parallel to the $c$ axis (paramagnetic case), the sign of the Hall coefficient changes from $n$ to $p$ type with increasing temperature. The reversal takes place at 165\ifmmode^\circ\else\textdegree\fi{}K. The Hall coefficient in the exhaustion range has a value \ensuremath{\sim}${10}^{\ensuremath{-}2}$${\mathrm{cm}}^{3}$/C which corresponds to ${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ carrier concentration. For samples with both their long axis and the magnetic field perpendicular to the $c$ axis (ferromagnetic case), no reversal of the Hall coefficient was observed and the material was $p$ type for all temperatures. The curve of the Hall resistivity ${\ensuremath{\rho}}_{H}$ versus the magnetic induction, for constant temperature, exhibits the typical form for ferromagnetic materials.