Positive magnetoresistance peaked at ferromagnetic transition in Mn-doped quantum wells GaAs/AlGaAs

A large positive magnetoresistance peaked at the Curie temperature was observed in quantum well structures GaAs/AlGaAs doped by Mn. We suggest a new mechanism of magnetoresistance within low $T_c$ ferromagnets resulting from a pronounced dependence of spin polarization at the vicinity of $T_c$ on the external magnetic field. As a result, any contribution to resistance dependent on the Zeeman splitting of the spin subbands is amplified with respect to the direct effect of the external field. In our case we believe that the corresponding contribution is related to the upper Hubbard band. We propose that the mechanism considered here can be exploited as the mark of ferromagnetic transition.