Antiferromagnetically Coupled Bilayer, Trilayer Magnetic Properties Of Micro-magnetic Study

This thesis, based on the micromagnetic theory, investigates the magnetization reversal processes of antiferromagnetically exchange coupled magnetic bilayer & trilayers.(1) The magnetic hysteresis properties of an antiferromagnetically exchange coupled trilayers are studied with in the framework of the Stoner-Wohlfarth model. we obtain the phase diagram of easy-axis hystersis loops of an antiferromagnetically exchange-coupled trilayers structures in different structural & magnetic parameters., we are discussed the hysteresis loop type and thermal stability of antiferromagnetic exchange coupling trilayers free layer and antiferromagnetic exchange coupling magnetic recording media.(2) The magnetization reversal processes and bending field of antiferromagnetically exchange-coupled soft/hard bilayer structures were studied based on the one-dimensional atomic chain model. We put forward &prove for the first the first time that there is irreversal process in the process of reversal magnetization of antiferromagnetically exchange coupled soft/hard bilayer structures. The result shows when soft layer is less than the thickness of a certain critical thickness t_c, soft layer reversal is a reversible process. When soft magnetic layer is more than the thickness of that critical thickness t_c, its reversal is an irreversible process. Morever, Only when soft layer is less that the critical thickness t_c, the bending field is determined by H_b = H_b0 /tⁿ (t is the thickness of the soft layer, H_b0 and n are constants for a given structure.),which is imentioned in documents.(3)By means of micromagnetic method, we study the magnetization revesal process of the antiferromagnetically exchange coupled free layer from the following three aspects. 1) under the condition of strong antiferromagnetically exchange coupled, when the aspect ratio is 1, the surface width changes from 100nm to 1000nm. If the surface more than 400, the magnetic reversal process is consistent reversal; Reverse field and Saturated field has nothing to do with the layer surface width. If the surface width is smaller than 400nm, the magnetic reversal process is unconsistent reversal; the reverse field and saturated field is reduce with the increased surface width. 2) When the surface width and the length are 400nm, with the increased antiferromagnetical exchange coupling, the magnetization reversal process from a complex process to a consistent reversal and the reverse field decreases then remain unchanged. For J = 1×10^-3 J/m², when the difference of the magnetic layer thickness is 3nm, with the increase of magnetic layer thickness, the reverse field is reduced and then increased. 3) We investigated the magnetization revesal process of free layer from two difference surface width when the aspect ratio is change. When the the surface width is 100nm, the reverse field and saturated field is reduce with the increased aspect ratio. When the the surface width is 400nm, the coercivity field is decreases then remain unchanged with the increased of the aspect ratio.