Resistivity of Lightly Doped Ferromagnetic Semiconductors
Tóm tắt
In metallic magnets with a low carrier density, scattering from magnetic fluctuations above and near the transition temperature T
c provides a large contribution to the electrical resistance. Because the fluctuations can be suppressed by a magnetic field, a large negative magnetoresistance ensues. In a simple model, we find the low field magnetoresistance scales with the ratio of field induced magnetization m(H) to the saturation magnetization m
sat: Δρ/ρ=(ρ(T, 0)−ρ(T, H))/ρ(T, 0)≈C(m/m
sat)2. At very low carrier densities magnetic polarons should form in a range of temperatures above T
c. The CMR perovskite manganites cannot be explained without strong coupling of the magnetic order to lattice distortions (of the Jahn–Teller type) above T
c.
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