Tunneling magnetoresistance in granular composites

摘要

The temperature dependence of magnetoresistance in insulating granular systems is studied. At low temperatures the magnetoresistance is enhanced drastically as a result of high-order tunneling. On the other hand, decay of spin polarization will lead to a decrease of magnetoresistance at high temperatures. The role of grain size distribution is investigated and the intergrain correlation is found very crucial in determining the magnitude of magnetoresistance. Our calculations agree with the experimental data well.