The study of magnon-drag effects in the thermopower of CuCr ₂X₄ (X = S, Se and Te)

The electrical resistivity ρ and thermopower S of metallic ferromagnets CuCr₂X₄ (X=S,Se or Te) are measured at low temperatures and in an external magnetic field of 1.5 Tesla. These properties are dominated by strong scattering effects in their ferromagnetic phase, resulting in (a) ρ(T) ∼A T²dependence with very large value of coefficient A ≈ 1 - 3×10^-8 Ω-cm/K² in resistivity and (b) a peak in the thermopower around T_C/3 . Thermopower is further increased by crystalline order and by the alignment of magnetic domains in an external magnetic field as has been found for Cu_1+x Cr ₂Te₄. We have interpreted these effects as due to strongly coherent momentum conserving electron-magnon scattering giving a large T ² - contribution in resistivity and a large drag effect in thermopower.