Transport-magnetism correlations in the ferromagnetic oxide La _0.7Ca_0.3MnO₃

We present results of temperature and magnetic field dependent resistivity ρ(H,T) and bulk magnetization M(H,T) measurements on post-annealed La _0.7Ca_0.3MnO₃ thin films that were grown via pulsed-laser deposition. Both the resistivity and the anomalously large negative magnetoresistance peak near the ferromagnetic ordering temperature (T _c=250 K), with Δρ/ρ₀=-85% at 50 kOe. A clear correlation is found between ρ and M that is described by the phenomenological expression ρ(H,T)∝exp[-M(H,T)/M₀]. This correlation reflects the important interplay between transport and magnetism in this system, and suggests that the transport below T_c involves polaron hopping.