Grain boundary magnetoresistance in the strong-disorder limit: A field-dependent critical path analysis

A field-dependent critical path method is applied to analyze the grain boundary magnetoresistance effects observed in strong-disorder materials. Magnetotransport properties are calculated by taking into account the variation of conductance distribution with the applied magnetic field. It is found that the nontrivial field dependence of percolation paths due to a broad conductance distribution will diminish the otherwise dramatic magnetoresistance enhancement in strongly disordered systems. Based on the critical path analysis, a strong-disorder limit around 63% is predicted on grain boundary magnetoresistance in the half-metallic case. The theoretical prediction is in good agreement with the results of Monte Carlo simulation.