Numerical Calculation Of Kerr Effect And Magnetoresistance For Nanomagnetic Materials

In this thesis the Kerr effect and magnetoresistance of nanomagnetic materials have been studied with numerical methods.The main contents of this paper are arranged asfollows:Firstly, we briefly present the knowledge of the magneto-optical effect and its experimental scheme, especially three mechanisms of the magneto-optical Kerr effects. Subsequently, we also expound the basical ideas of the magnetoresistance, especially for giant magnetoresistance of the granular films. Additionally, we describe the 4×4 matrix method and Monte Carlo simulation technique in the second chapter.Secondly, with the 4×4 matrix method and the theory of the equivalent layer, the Kerr effects for (TbFeCo)_100-xPr_x magnetic multilayered-films, as a function of interfacial layer, the thickness of magnetic layer and the incident angle, have been simulated. It is found that the structure of interface played an important role for magneto-optical effects in magnetic multilayered filmThirdly, based on the Monte Carlo and 4×4 matrix method, we present the theoretical calculation of the Kerr loops and giant magnetoresistance curves in granular films.The calculated results of both Kerr loops and GMR curves are in good agreement with experimental ones.On one hand, the experimental hysteresis loops for Ni_xSiO_2(1-X) granular films are calculated. The simulated results reveal that: generally, the difference between the hysteresis loops measured from VSM and Kerr effect respectively always exists for certain incident angle; the difference increases with increasing incident angle; it is smaller in strong ferromagnetic films than that in weak or mixed magnetic films.On the other hand, the Kerr loops and giant magnetoresistace curves in Co_xAg_1-X granular films are calculated. The simulated results reveal that: the anisotropy energy and the dipolar interaction influence evidently the Kerr loops and the giant magnetoresistace effect; the value of K₁ for the Co_xAg_1-x granular films are calculated, which plays animportant role for explaining the giant magnetoresistace effect of the granular films. It should be pointed out that the constant K, is related with the resistivity at a zero field and the scattering parameter constant.Fourly, based on Monte Carlo simulations and resistor network model, the tunneling magnetoresistance (TMR) for the square anisotropic magnetic nanoparticle arrays has been studied. The simulated results reveal that: with the exchange coupling J, for small dipolar interaction, the value of TMRniix decreases with increasing value of D, while it increases with increasing value of D for large dipolar interaction. Those behaviors can be explained with the competition of the different energies, including the random anisotropy, exchange and dipolar energies.