Transport and Magnetoresistance in Low Carrier Density Ferromagnets |
| P.B. Littlewood Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, England and Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, USA |
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| In metallic magnets, scattering from magnetic fluctuations above and near TC may provide a substantial contribution to the electrical resistance ρ(T). However, this effect is usually small because the dominant fluctuations are near q ≈ 0, which does not produce substantial backscattering across the Fermi surface unless 2kF is itself small; such a situation can be realised in metallically-doped ferromagnetic semiconductors. A simple adaptation of the theory of deGennes and Friedel shows the low field magnetoresistance scales with the ratio of field induced magnetisation m(H) to the saturation magnetisation msat: Δρ/ρ ≈ C(m/msat)2, where C ≈ x-2/3, with x the number of charge carriers per magnetic unit cell. Comparison to data on very different ferromagnetic metals and doped semiconductors is in broad quantitative agreement with this trend, with the prime exception of the perovskite manganese oxides, already understood to involve the extra physics of dynamic lattice distortions. At very low doping, the physics should involve ferromagnetic polarons, and polaron formation and transport are discussed. |
| DOI: 10.12693/APhysPolA.97.7 PACS numbers: 75.70.Pa |