Peculiarities of the electronic transport in half-metallic Co-based Heusler alloys

Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co${}_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn, Sb) were studied in the temperature range 4.2–900 K and in magnetic fields of up to 100 kOe. It was found that varying Y in affects strongly the electric resistivity and its temperature dependence $\rho (T)$, while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in $\rho (T)$ near the Curie temperature $T_C$. At $T<T_C$, the $\rho (T)$ behavior can be ascribed to a change in electronic energy spectrum near the Fermi level. The coefficients of the normal and anomalous Hall effect were determined. It was shown that the latter coefficient, $R_S$, is related to the residual resistivity ${\rho }_0$ by a power law $R_S\sim {\rho }_0^k\mathrm{/}{M}_S$ with $M_S$ the spontaneous magnetization. The exponent $k$ was found to be 1.8 for Co${}_2$FeZ alloys, which is typical for asymmetric scattering mechanisms, and 2.9 for Co${}_2$YAl alloys, which indicates an additional contribution to the anomalous Hall effect. The temperature dependence of resistivity at low temperatures is analyzed and discussed in the framework of the two-magnon scattering theory.