NEGATIVE MAGNETORESISTANCE IN P-TYPE BETA-FESI2 SINGLE-CRYSTALS IN 2 REGIMES OF VARIABLE-RANGE-HOPPING

Single crystals of p-type beta-FeSi2 demonstrate the negative magnetor esistance below 40 K that increases with decreasing temperature and do es not reach either a maximum or a saturation up to at least 12 kOe. T his effect is observed in both the Mott and the Shklovskii-Efros varia ble-range hopping regimes. At fields below approximately 3-5 kOe (depe nding on the temperature) the magnetoresistance displays a quadratic d ependence on the magnetic field, while at higher fields the dependence is linear. The experimental data are analyzed using two different app roaches to the interference effects in hopping conductivity in a magne tic field.