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

TL;DR

This study investigates the electrical and magnetic properties of Co-based Heusler alloys across a wide temperature range, revealing how Y element variation influences resistivity and Hall effects, with implications for electronic spectrum and scattering mechanisms.

Contribution

It provides new insights into the dependence of resistivity and Hall effect coefficients on composition and temperature in Co$_2$YZ alloys, highlighting different scattering mechanisms.

Findings

Y variation affects resistivity and its temperature dependence.

The anomalous Hall coefficient relates to residual resistivity via a power law.

Different scattering mechanisms are indicated by the exponent k in Co$_2$FeZ and Co$_2$YAl alloys.

Abstract

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 $R_S \sim \rho_0^k/M_S$ 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.