(The Magnetization Reversal Mechanism And Eigen Magnetic Dynamics Features Of Exchange-coupled Soft/Hard Magnetic Bilayers Structure)

Abstract:Exchange-coupled soft/hard multi-layers structure is a new kind of permanent magnet material and high-density storage mediums, due to its high magnetic energy and excellent thermal stability. This thesis researches into the magnetization reversal mechanism and eigen magnetic dynamics features of the exchange-coupled soft/hard bilayers structure by exploiting the micro magnetic theory and numerical simulation method.(1)The magnetization reversal mechanism of exchange-coupled soft/hard bilayer system have been studied using a discrete one-dimensional atomic chain model. We receive hysteresis loop with different structural parameters and magnetic parameter. It is found that magnetization reversal process is closely associated with the thickness of the soft layer and the strength of soft/hard magnetic interfacial exchange coupled. For structures with thin soft layers, the bilayer structure exhibits typical reversible exchange-spring behavior. However for the bilayers with thicker soft layers, the exchange-spring process becomes irreversible. For a given thickness of the soft layer, there is a critical interfacial exchange coupled strength Acsh.When interfacial exchange coupled strength is above Acsh, the exchange-spring process is reversible; Whereas after AcSh, the exchange-spring process becomes irreversible. The bending field of reversible and irreversible exchange-spring magnetization reversal process dependence of the thickness of the soft layer and the strength of soft/hard magnetic interfacial exchange coupled were present.We investigate the magnetic dynamical properties for exchange-coupled soft/hard bilayer structure in the magnetic exchange-spring process based on the Landau-Lifshitz equation, using a one-dimensional atomic chain model. We evaluate the frequencies as well as spatial distribution characteristics of different pinned situation magnetic eigenmodes for the system with uniform magnetic structure and spiral structure during exchange-spring process. Also, the corresponding spin wave dispersion relation is calculated. It is found that the magnetization reversal mechanism is closely related to soft mode of spin wave. The magnetization reversal of the soft layer is induced by softening of the first-order spin wave mode, and reversal process is closely related to the spatial distribution of the soften mode. When the strength of soft/hard magnetic interfacial exchange coupled is lessened, ie lessening the pinning strength on soft layer, the first-order self-spinning wave mode tends to be uniform distribution, and the magnetization reversal process also turns from exchange-spring magnetization reversal process to uniform magnetic reversal. The numerically calculated critical field required to soft the first-order spin wave mode agrees well with the result of analytic solution.