The Effect Of Anisotropic Gradient On The Magnetic Properties Of Hard/Soft Multilayers

In this thesis，magnetization distributions，hysteresis loops and angulardistirbutions have been calculated systematically for FePt(60nm)/Fe(5nm) bilayer，FePt(30nm)/Fe(10nm)/FePt(30nm) trilayer and [FePt(6nm)/C(l，2，3，4，5nm)]5/Fe(5nm)/[C(5，4，3，2，1nm)/FePt(6nm)]5gradient film (multilayer structure) inperpendicular and parallel orientation. Main results for this work are as follows:1)In the demagnetization process, the magnetic moment deviates from the edge withperpendicular and parallel orientation; for perpendicular orientation, the magnetizationof FePt(60nm)/Fe(5nm) bilayer displays vortex state，the magnetization of FePt(30nm)/Fe(10nm)/FePt(30nm) trilayer is in the S state，and the magnetization of [FePt(6nm)/C(l，2，3，4，5nm)]5/Fe(5nm)/[C(5，4，3，2，1nm)/FePt(6nm)]5gradient filmreverse from the same direction to completely deflection. For parallel orientation, themagnetization of bilayer displays symmetrical C and leaf states. The magnetization oftrilayer and gradient film only displays symmetrical C state; different distributions ofmagnetic moments are closely related to the oirentation of the applied field，the easyaxis orientation, the magnetocrystalline anisotropy gradients, the shape anisotropy andother factors.2)From the angular distribution, we can find the similarities of the perpendicular andparallel orientations: bilayer nucleation can be seen in sotf magnetic surface, whiletrilayer and gradient film can be seen in the center of the soft phase; angulardistirbutions of trilayer and graded film both symmetrically decrease in the soft phasecenter; because the exchange-coupling at interface is very strong, angle moment is acontinuous process.We can also find, from the angular distirbution, the difference between them: whenthe applied field H decreases，domain wall movement is higher in perpendicular, whosemain reason is demagnetization. 3)From the magnetic hysteresis loops, for the perpendicular orientation, bilayer istreated as exchange spring magnet because of the strong interface exchange-coupling inthe demagnetization process, and trilayer is treated as a decoupling magnet; whilegradient film is treated as a rigid magnet because of its stronger exchange couplingeffect. For the parallel orientation, hysteresis loops are almost rectangular, it shows thatthe exchange coupling effect of this kind of oirentation is stronger.4)Through analysis of the coercivity，for perpendicular orientation，we find thatbecause of the exchange coupling at the interface, coercivity of FePt (60nm)/Fe (5nm)bilayer is smaller than FePt monolayer; coercivity of trilayer is smaller than the bilayer,because the trilayer nucleation occurs in the center of the sotf magnetic phase. With thehelp of the sotf magnetic phase，the hard phase can reverse under weaker field; thecoercivity of the gradient film is weaker than the one of the trilayer, because theformation of gradient modulus FePt-C and sotf magnetic Fe cause a quasi continuousvariation of Ku, Ku difference will lead to low coercive force. Under parallel orientation,nucleation field and coercive force are smaller than these of the vertical orientation. Inparallel orientation，trilayer coercivity is equal to the bilayer one, which is differentfrom the perpendicular orientation. This difference is mainly due to the influence ofdemagnetization.