Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co2YZ (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 Co2YZ alloys affects strongly the electric resistivity and its temperature dependence ρ(T), while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in ρ(T) near the Curie temperature TC. At T ≤ TC, the ρ(T) behavior can be ascribed to a change in electronic energy spectrum near the Fermi level. The coefficients of normal and anomalous Hall effect were determined. It was shown that the latter coefficient, RS, is related to the residual resistivity ρ0 by a power law RS ~ ρ0 k /MS with MS the spontaneous magnetization. The exponent k was found to be 1.8 for Co2FeZ alloys, which is typical for asymmetric scattering mechanisms, and 2.9 for Co2YAl alloys, which indicates an additional contribution to the anomalous Hall effect. The type of the temperature dependence ρ(T) is analyzed and discussed in the frame of two-magnon scattering theory.

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The residual resistivity, Hall effect, and magnetization of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were considered at T = 4.2 K and in fields up to 100 kOe. It is shown that as the number of valence electrons z ranges from 26 to 32, significant changes in the residual resistivity ρ0, magnetization Ms, sign and magnitude of the normal R0 and anomalous RS Hall effect coefficients are observed during the transition from Co2TiSi to Co2NiSi. It is established that there is a clear correlation between the values ρ0, R0, RS and Ms, depending on the number z, which can be associated with the appearance of a half-metal ferromagnetic state and/or spin gapless semiconductor. As z changes, the anomalous Hall effect coefficient has a power-law dependence on the residual electrical resistivity with an exponent of k = 3.1, which diverges with existing theories but agrees well with the experimental data obtained earlier for similar half-metallic ferromagnetic Heusler alloys.

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