| Until now researchers have not come to the common conclusion to explain the origin of colossal magnetoresistance (CMR) effect which is used to describe the very large, magnetic field driven changes in electrical resistivity in perovskite manganites. However there is now general consensus that the CMR transition is a type of percolation that the ferromagnetic clusters percolate the paramagnetic background. Due to the double-exchange process, the ferromagnetic clusters become metallic clusters that cause the insulator-metal (I-M) transition. Applying magnetic field accelerate the percolation process which leads to the intrinsic CMR effect. To study the formation of percolation entities, Griffiths theory is used to describe the influence of Griffiths phase on the electrical transport properties and magnetic properties of these samples.This dissertation have studied the mechanism of Griffiths phase, discussed the existence of this phase in these samples and illustrated the influence of this phase on the transport properties of these samples. This dissertation provides the detailed coverage of1. This chapter has introduced the Griffiths theory and the development of recent researches of Griffiths phase on colossal magnetoresistance materials. The dynamic phase segregation also has been described in this chapter.2. The mechanism of Griffiths phase is mainly discussed in this chapter. The dynamics of spin autocorrelation function and the non-equilibrium decay of magnetization in the Griffiths phase of both 2D and 3D randomly site dilute Ising magnetic systems are studied by Monte Carlo simulation.3. According to the Griffiths theory, there is always a finite probability of finding short range ferromagnetic clusters which are segregated within the paramagnetic matrix for the temperature of T_C |
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