Sign reversal in the field dependence of the Hall effect in YZn at liquid-helium temperatures

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The Hall effect has been measured on single crystals of the ordered alloy YZn at room temperature and liquid-helium temperature, in magnetic fields up to 2.2 T. The room-temperature Hall resistivity is positive and increases linearly with field. At liquid-helium temperatures, the Hall resistivity is negative at low fields and reverses its sign near 0.7 T. The two-band model allows a good understanding of these results, which complete and confirm previous knowledge of the Fermi surface of this alloy based on the de Haas-van Alphen effect. The combined results show that the electronic structure of YZn consists of a small spherical sheet, containing 5.9 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ highly mobile electrons per unit cell (this number can be obtained from the two-band model or the de Haas-van Alphen effect with remarkable agreement) probably located at $R$ in the Brillouin zone, and of a multiply connected hole sheet of lower mobility, with the topology of intersecting cylinders probably directed along $\ensuremath{\Gamma}X$, corresponding to a zone approximately half-filled.