The Hall effect and thermoelectric power correlated with the giant magnetoresistance in modified FeRh compounds

Simultaneous measurements of the magnetoresistance, magnetization, Hall effect, thermoelectric power and specific heat of a modified FeRh compound where 3.5 at.% Ni is doped at the Fe sites are investigated in order to elucidate the origin of the giant-magnetoresistance phenomena through the metamagnetic transition from the antiferromagnetic (AF) to the ferromagnetic (F) state. The Hall coefficient changes its sign through the metamagnetic transitions. The sign of the thermoelectric power also changes from positive to negative through the transition from the AF to the F state. The electronic specific heat coefficient increases remarkably through the metamagnetic transition from the AF to the F state. These results imply that the giant-magnetoresistance effect in FeRh compounds results from the reconstruction of the Fermi surface across the metamagnetic transition. At low temperatures, two-step metamagnetic transitions were found, suggesting an uncompensated AF or ferrimagnetic state in the intermediate-field region around 2-3 T, only in the process of increasing the field.