An Experimental And Theoretical Studies Of Non-Uniform Magnetization And Excitation

Studies on magnetic properties of patterned arrays with submicron size elements have been carried out in recent years due to the potential application in magnetic random access memory (MRAM) and ultrahigh density data storage of magnetic thin and ultrathin film. Magnetic properties of arrays with submicron elements including the hysteresis loop, switching field and saturation field as well as magnetic anisotropy etc. are very important for applications. These properties are related to the shape, size of the submicron element and separation between the elements. In this thesis, systematic studies on the magnetic properties, especially magnetic anisotropy and nouniform demagnetizing field by means of MOKE, FMR, FMR spectra and other analysis methods as well as micromagnetic theoretical calculation. The major results are summarized as follows.1. Experimental studies on magnetic properties of permalloy submicron arrays of rectangular elements prepared by electron beam lithographyScanning Electron Microscopy (SEM) identified the composition and shape of our samples. The morphology showed that the sizes of the element in patterned films are 300nm wide with the aspect ratio of1, 2 and 4. By FMR and MOKE as well as theoretical simulation of FMR data, the magnetic properties of samples was studied. We found that in the patterned submicron rectangular elements an in-plane anisotropy appeared clearly, which was originated from uniform magnetization and the non-uniform magnetization of non-elliptical elements. The contribution from the non-uniform magnetization decreased when the aspect ratio increased. The easy magnetization axis was along the long edge (square edge for square element) of the rectangular element and the hard axis was along the short edge (diagonal for square element) of the rectangular element. When the width of the element of patterned films was fixed, the magnitude of in-plane anisotropy increased with the aspect ratio. When the aspect ratio of element in patterned films was fixed, the magnitude of in-plane anisotropy increased as the width of element decreased. When the steady magnetic field was applied near the film normal, a series of peaks appeared on the low field side of the main peak for all samples. The multi-peak spectra are related to the excitations of non-uniform magnetization modes due to non-uniform demagnetizing field and magnetization in the small rectangular patterned element.2. Micromagnetic numerical calculations of demagnetizing field in rectangular element.The magnitude and direction distributions of demagnetizing field in the 10nm thick, 300nm wide rectangular elements with 1, 2 and 4 aspect ratio as well as the interactions among different elements were studied by micromagnetic numerical calculation. The results showed that the non-uniform demagnetizing field did exist in the non-ellipsoidal element. The uniformity increased with the aspect ratio if magnetic field was along any direction. The demagnetizing field in the center of the element was more uniform than that at the edge.