Multi-band effect in the noncentrosymmetric superconductors Mg_(12-δ)Ir₁₉B₁₆ revealed by Hall effect and magnetoresistance measurements

We report the longitudinal resistivity and Hall effect measurements on the noncentrosymmetric superconducting Mg$_{12-\delta}$Ir$_{19}$B$_{16}$ samples with different critical transition temperatures. A strong temperature dependence of the Hall coefficient $R_H$ and nonlinear magnetic field dependence of the Hall resistivity $\rho_{xy}$ in wide temperature region are observed, suggesting a strong multi-band effect in this system. Moreover, a large magnetoresistance up to 20% is found at the field of 9 T. We also observe the violation of the Kohler's rule from our magnetoresistance data, further confirming the presence of multi-band effect in our samples. A detailed analysis shows that the data can't be simply described within the two-band scenario at low temperatures, so we argue that there may be more than two bands contributing to the conduction of the samples.