Low-temperature resistivity, magnetoresistance, and domain-wall resistance of highly pure single- and polycrystalline iron

摘要

On a set of 12 bulk and highly pure [residual resistance ratio (RRR) up to 6000] iron single crystals with different crystallographic orientation and on polycrystalline material the "hidden" basic resistivity ρ(T,B → 0) and magnetoresistive effects (anisotropic magnetoresistance, longitudinal and transverse Lorentz resistance) are quantitatively disentangled. The temperature-dependent basic resistivity for T ≤ 30 K follows a Δρ(T,B → 0) = aT~2 + bT~5 law, proving that electron-electron and electron-phonon scattering (with a resistive Debye temperature Θ_R ≈ 450 K) are dominant also in iron, similar to nowferromagnetic transition metals. Here the crystal-orientation dependence of the intrinsic longitudinal magnetoresistance in the single-domain state could be quantitatively evaluated in accordance with the symmetry of the Fermi surface. The transverse magnetoresistance (TMR) turns out to be the sum of the so-called "two-band conduction term" and the unboundedly growing TMR term in compensated metals. It is proven that the second term is not restricted to the high-field limit (as usually discussed up to now) but acts down to lowest TMR or ω_Cτ values. This conclusion is verified by TMR measurements on highly pure molybdenum single crystals (RRR ≈ 100000). Supported by Kerr microscopy, a small positive domain wall resistance (DWR) could be isolated from the dominating negative DWR in the multidomain state of iron, resulting in a relation of larger than 5:1 for the electrons to pass a domain wall with spin tracking compared to scattering with spin conservation.