Magnetization Characteristics Of Magnetic Thin Film Systems And The Spin-wave Nature Of The Study

Nowadays, hard disk driver storage technology is one of the most important technologies for information processing and exchange bias is one of essential physical mechanisms in the basic structures of hard disk driver head and magnetic random access memory (MRAM) at present. In order to understand the origin of this phenomenon and improve the properties of recording media, experimental and theoretical study on ferromagnetic/antiferromagnetic bilayer system is very important.Progress in magnetic recording led to the development of patterned recording media and its ability of recording individual bits of information. At the same time, rapid increase of processor speeds in modern computers leads to the necessity to write bits of information during subnanosecond time intervals. To achieve this time scale in writing process, one can take advantage of the so-called precessional remagnetization, where the remagnetizing field is applied for a time interval, which is determined by the resonance frequencies of the patterned media. Thus, the theoretical and experimental study of the eigenfrequencies of spin wave excitations in the patterned recording media is of great importance.Because of the importance of magnetic properties and spin wave excitation in bounded magnetic films on theoretical research and practical applications, we choose"the magnetic properties in exchange-biased system and spin wave excitations"as our thesis. The thesis contains two main works:Firstly, exchange anisotropy in FM/AFM bilayers has given a lot of static magnetization properties such as enhanced coercivity and magnetization loop shifts. These phenomena are primarily from the effective anisotropies introduced into a ferromagnet by exchange coupling with a strongly anisotropic antiferromagnet. These effective anisotropies can also be used to explain the dynamic consequences of exchange-biased bilayers. In this thesis, the dynamic consequences such as exchange-induced susceptibility, exchange-induced permeability and the corresponding domain wall characteristics in the exchange-biased structures of ferromagnet/antiferromagnet1/ antiferromagnet2 are studied. The results show that the second antiferromagnetic layer can largely affect the dynamic consequences of exchange-biased bilayers. Comparing to the exchange-biased bilayer, for the exchange-biased trilayer the domain wall width decreases while the domain wall energy and domain wall mass both increase. The corresponding domain velocity decreases but the susceptibility increases, especially in the case of critical temperature, the effects become more obvious. Practically, the exchange anisotropy of biased bilayer system can be tuned by exchange coupling with the second antiferromagnetic layer.Secondly, we study the propagating properties of spin wave in metallic stripe, whose width and thickness is confined and length is infinite. Therefore, using the Landau-Lifshitz equation, the propagating properties of spin wave in metallic magnetic stripe has been investigated, in which the effective boundary condition is applied for the dynamic magnetization of the metallic magnetic stripe. The relationship between spin wave spectrum and width of the stripe has analytically been derived. Numerical calculations show that in-plane confinement results in the obvious kinks in the threshold curves. And with the increase of stripe width, the kink numbers almost rise in exponential, while the threshold jump at the first kink is nearly in inverse proportion to its width. Since the threshold is connected with intrinsic magnetic losses in the material, the threshold curve can be used to determine magnetic losses in a material.