強磁性体の磁化揺らぎによるスピン依存電気抵抗

概要

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Spin-dependent electrical resistivities ρ↑, ρ↓ of bcc-Fe based on scattering due to magnetic fluctuation below the Curie temperature were calculated using first-principles methods. The tight-binding linear muffin-tin orbital method with local spin-density approximation was employed to calculate the electronic structure. The spin fluctuations within the static (adiabatic) approximation corresponded to the local spin disorder, which can be treated using the coherent potential approximation. The Kubo-Greenwood formula was used to calculate the electrical resistivity in each spin state based on the electron scattering by magnetic fluctuations. The obtained results indicated that the ferromagnetic states of bcc-Fe in finite temperature are characterized as a classical spin system such as the Heisenberg model, although the electronic structure calculations are carried within the itinerant electrons system. The total electrical resistivities ρ = ρ↑ρ↓/(ρ↑ + ρ↓) which are on the basis of the two-current model show qualitative agreement with the experimental measurement as a function of temperature. Furthermore, the spin asymmetry coefficients β = -(ρ↑ - ρ↓)(ρ↑ + ρ↓) exhibited a remarkable behavior that the sign changed from positive to negative in the finite temperature region below the Curie temperature.