Computer Simulation Of The Magnetoresistance Effect

Among the numerous materials with the giant magnetoresistance effect, magnetic granular film enjoys great popularity in practice because its simple and convenient technological preparation. In this thesis, the giant magnetoresistance effect and the magnetization process of the metal-insulator granular film are investigated using the Monte Carlo method. In chapter four, on the basis of Stoner-Wohlfarth model, the different states of the (superparamagnetic or ferromagnetic) particles are distinguished. Using the Monte Carlo method, the balance states of the superparamagnetic particles are simulated and the magnetization process of the magnetic granule system is studied. The main results are: The hysteresis loop of the magnetic granular film systems without interparticle interactions is caused by the ferromagnetic particles as a result of the irreversible transitions between states of minimum energy. The enhanced dipolar interaction for the reduction of the distance between magnetic particles and wide particle-size distributions will suppress the magnetization. There is some deviation in the description of magnetization curve of the system with the classical Langevin function. With the number of layers increasing, the magnetization turns easy in the vertical direction, while that inside the film plane becomes difficult. Only taking into account of the magnetic moment correlations of the nearest particles and applying the improved Inoue theory, the giant magnetoresistance effect of metal-insulator granular film are studied using the Monte Carlo method in chapter five. The main conclusions are: the magnetic transport properties of the system are determined by magnetic anisotropy energy, dipolar interaction energy and Zeeman energy. The enhancement of the dipolar interaction can suppress the giant magnetoresistance effect. As to the magnetic field applied in the normal direction to the film plane, the magnetoresistance of the system increase more rapidly as the number of layers increases. The present results are analyzed based on the understanding of the magnetic and transport properties in granular films.