Micromagnetic Analysis Of The Influence Of The Easy Axis Orientation And Soft Layer Crystallographic System On The Demagnetization Process In Hard/soft Trilayers

In this thesis, the magnetic properties of hard/soft trilayer systems under different soft crystallographic systems have been calculated systematically by a micromagnetic simulation method. We investigated two soft crystallographic systems: one is the uniaxial soft layer in a hard/soft/hard trilayer system(Sm2Co17/α-Fe/Sm2Co17); the other one is the cubic soft layer in another hard/soft/hard trilayer system(Nd2Fe14B/α-Fe/Nd2Fe14B). For each corresponding β, we obtained the spin distribution, hysteresis loop and energy product of these two systems, where β is the angle between the easy axis and the applied field. The main results of the research are as follows:(1) When β = 0°, with Nd2Fe14B/α-Fe/Nd2Fe14 B taken as a model(while α-Fe is either uniaxial or cubic), in order to analyze the magnetic properties of the system under low magnetic field, we utilized Taylor series to expand the magnetization derivation angle θ around angle β, and obtained the theoretical expression of the magnetization spatial distribution within the simulated material. Furthermore, we compared this to the situation when β = 0°. We found that with a low magnetic field, when β≠0°, the magnetization is more sensitive to the magnetic field. With the increase of β, the deflection angle becomes bigger.(2) With the consideration of a uniaxial soft layer, we investigated the influence of β on the spin distribution, hysteresis loop and energy product in trilayer systems. Simulations indicate that β has a clear influence on the magnetization reversal process, pinning field and remanence. When β increases, the remanence of the system decreases, and the variations of the squareness of the hysteresis loop lead to a decrease of the maximum energy product of the system. In this thesis, with the study under different thin layer thicknesses, the variation of the pinning field is found to be related to β, and increases as β increases. The coercivity first increases then decreases following the increase of β, in addition a peak appears at β = 30°.(3) With the consideration of a cubic soft layer, the influence of β on the demagnetization process of such trilayer systems is similar to the situation where the soft layer has a uniaxial anisotropy, the remanence is the same, and the pinning field increases as β increases. Without magnetic field, all the magnetic moments are all aligned along the easy axis direction in both kinds of system. When the external field is smaller than zero, the soft layer internal magnetization rotates fastly, and because of the exchange-coupling effect, a reversal of the hard layer magnetization occurs. The soft layer cubic anisotropy makes the magnetization to be more sensitive to the applied field. In addition, the pinning field and maximum energy product are higher within cubic soft layers than in uniaxial soft layers.