The Effect Of The Easy Axis Orientation On The Magnetic Properties Of Hard/Soft Multilayers

In this thesis, magnetization distributions, hysteresis loops and energy productshave been calculated systematically for a hard/soft multilayer system(Nd₂Fe₁₄B/α-Fe)with a deviation of easy axis β taken into account, where β is the angle between the easyaxis and the applied field. Main results for this work are as follows:1) The effect of the deviation of easy axis β on the pinning field and the energyproduct of the multilayers has been investigated with ignoring the effect of the hardphase on the demagnetization. The calculations show that the deviation of the easy axisβ affects the reversal process of the magnetization, the remanence as well as the pinningfield significantly. When β≠0°, there is no obvious nucleation point in contrast with thecase of β=0°. Magnetizations in the multilayer system orient at the same direction （θ≡β） only at the remanence state （H=0）. When the applied field H decreases, themagnetization of the soft phase deviate rapidly and drives the magnetization in the hardphase by the exchange-coupling at the interface. The pinning field has a peak for smallLsand increases monotonously for large Lswhen β increases. Both remanence andcoercivity decreases as β increases, leading to a sharp decrease of the energy product.2) The demagnetization process in a hard/soft multilayers system has beeninvestigated with the thickness of hard phase and the deviation of easy axis as the mainvariables. There is no clear nucleation point due to the non-zero value of β. Themultilayers system can never reach the saturation; it can only infinitely approach thesaturation. When the applied field is positive, the angle in the center of the hard layer islargest and the one in the center of the soft layer is smallest because of the differentanisotropy. To analyse the effect of the hard thickness on the demagnetization process,the hysteresis loops of the multilayers with different hard thickness have been computedby Stoner-Wohlfarth model and the equations. The results show that the effect of thehard thickness can not be ignored when it is comparative small. When the hard thickness is large （larger than10nm）, the results of two different methods are in goodagreement with each other, which indicates that the thickness of hard layer can beconsidered as an infinite value and its effect on the demagnetization process can beignored. The remanence and the coercivity of the multilayer system decrease with β,which directly lead the decrease of energy product. The change tendencies of thepinning fields are different for the multilayers with different soft thickness, which canbe used to judge whether the multilayers is an exchange-coupled magnetic composite.