Tunneling magnetoresistance of phase-separated manganites

The mechanisms underlying the magnetoresistance of non-metallic phase-separated manganites are analyzed. The material is modeled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in an insulating matrix. The concentration of metallic phase is assumed to be far from the percolation threshold. The electron tunneling between ferrons causes the charge transfer in such a system. The magnetoresistance is determined by the effect of the magnetic field H on the tunneling probability related to the changes both in the size of ferrons and in the mutual orientation of their magnetic moments. It is shown that the low-field magnetoresistance is proportional to H2 and decreases with temperature as T-n, where n can vary from 2 up to 5 depending on the parameters of the system. In the strong-field limit, the tunneling magnetoresistance grows exponentially, but the crossover between these two regimes can correspond to a plateau