Carrier density variation in films of Nd 0.5 Sr 0.5 MnO 3

The carrier density in thin films of Nd 0.5 Sr 0.5 MnO 3 , as derived from Hall measurements, shows a distinct change at the paramagnetic (PM)-ferromagnetic (FM) transition around T C = 225 K. In the PM-semiconducting regime the density is n = 0.30 holes per unit cell and increases in the FM-semimetallic regime to n = 0.49. The magnetoresistance effect in the semimetallic phase is due to a field-induced increase of the carrier mobility, while the carrier density is unaffected. In the low-field limit an extraordinary enhancement of the ρ xy ( B ) slope due to the anomalous Hall effect is observed. The spontaneous Hall resistivity ρ xy ⋆ , reflecting the strength of the asymmetric scattering between carriers and localized magnetic moments, is linked to the zero-field resistivity ρ xx via ρ xy ⋆ ∝ ρ xx 1.74 .