Abstract
The magnetoresistance and the noise power of non-metallic phase-separated manganites are studied. The material is modelled 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 tunnelling between ferrons causes the charge transfer in such a system. The magnetoresistance is determined both by the increase in the volume of the metallic phase and by the change in the electron hopping probability. In the framework of such a model, the low-field magnetoresistance is proportional to H 2 and decreases with temperature as T −n , where n can vary from 1 to 5, depending on the parameters of the system. In the high-field limit, the tunnelling magnetoresistance grows exponentially. Different mechanisms of the voltage fluctuations in the system are analysed. The noise spectrum generated by the fluctuations of the number of droplets with extra electrons has a 1/ f form over a wide frequency range. In the case of strong magnetic anisotropy, the 1/ f noise can also arise due to fluctuations of the magnetic moments of ferrons. The 1/ f noise power depends only slightly on the magnetic field in the low field range whereas it can increase as H 6 in the high-field limit.
Published Version
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