| Nowadays, micromagnetic modeling has become a useful tool in studyingand designing the magnetic devices in hard disk drives for ultra-high densitymagnetic recording, such as the magnetic recording media, the magnetic read andwrite heads and the magnetic recording systerms, etc. In this dissertation, weusing the micromagnetic simulation method for analysing the core magneticdevices in magnetic hard disk drives, including the L10 ordered FePt perpendicularrecording media, the current-perpendicular-to-plane giant magnetoresistance readheads, and the heat assisted magnetic recording system. Thus, the dissertation isdivided into three parts:Part 1: Micromagnetic Analysis of The Magnetic Recording Media Used forUltra-High Density RecordingIn this work, a 3D micromagnetic model is set up for the FePt monolayer andmultilayers deposited by magnetic sputtering experimental methods. The basicmagnetic characteristics of the FePt medium is analyzed according to therelationship between the magnetic property and the microstructure, with carefuldiscussions of the tetragonal structure and the magnetostriction. The simulationresults agree well with experiments. The main results are as follows:1) In the FePt/Pt/CrW monolayer, when the W content in the Cr underlayer is increased from 0% to 15%, the misfit between the Cr(200) and FePt (001) planes increases from 5.4% to 7.2%, which suggests that the intrinsic stressσi exits in the FePt phase's film plane. Through the qualitative analysis of the film stress, it is concluded that the total stress in the FePt phase's film plane is about 1.079 GPa, which contains both the thermal and intrinsic components of stress, and total film stress along the FePt phase's a-axis is about 763 MPa. 2) In the FePt/Pt/CrW monolayer, we studied the role of tetragonal anisotropy, stress and inter-grainular exchange on the M-H loop properties by using the micromagnetic method.3) In the Fe/Pt Multilayers, the simulated M-H loops agree well with the experiments. It is found that the c-axis deviation from the film normal direction is smaller in Fe/Pt Multilayers, compared with the FePt/Pt/CrW monolayer,however,the monolayer has narrower Hka distribution and larger exchange interactions among the magnetic grains and across the grain boundaries, both of which agree with the experiments. The simulated perpendicular coercivity of Fe/Pt Multilayers is about 7.8 kOe, a little smaller than the in-plane coercivity, which is mainly caused by the large in-plane crystalline anisotropy field.4) In the Fe/Pt Multilayers, The coercivity mechanism is analyzed by using the micromagnetic model, it is found that the domall wall motion plays an important role on the coercivity mechanisms.5) Furthermore, a 3D micromagnetic model is built up to analyze the relationship between the magnetic property and the microstructure of CoCrPt thin films, with careful discussions of the uniaxial symmetry and the magnetostriction. It is found that magnetostriction effects play an important role on the coercivity mechanisms when the Pt content is more than 15 at%Part 2: Micromagnetic Modeling For Current-Perpendicular-to-Plane GiantMagnetoresistance Read HeadIn this part, a micromagnetic model is performed to find the propergeometrical and magnetic parameters for current-perpendicular-to-plane giantmagnetoresistance (CPP-GMR) spin-valve heads with suitable longitudinalbiasing schemes at higher recording densities. The main results are as follows: 1) For optimum biasing, at the side edges of the free layer, the biasing field in the film norm direction must be reduced to prevent the multi-domain formation in the free layer. So the optimal value of the pitch angleθfor the PM design calculated here is 70°.2) When the GMR sensor width is reduced to 40nm, the magnetization of the free layer rotates coherently in response to the excitation fields at various height to width ratios. When h/w(height to width ratio)is more than 1, the shape anisotropy plays an important role in the magnetization reversal process, which will cause hysterical and irreversible jumps in the MR transfer curves, and will deteriorate the sensitivity of the head signal output.3) The respective calculated MR transfer curves is studied at various h/w ratios and different Mrδvalue of the abutted permanent magnets with track width W=40 nm.4) We also studied the imaging effect related to the two magnetic shields on the calculated M-H loops of the spin-valve multilayers. When the shield-to-shield gap length G is reduced to 20nm, the Hpinned≥700Oe and HsyAF≥1000Oe are needed for optimal designing of the spin value GMR sensors.Part 3: Micromagnetic Modeling for Heat Assisted Magnetic RecordingHere, a micromagnetic model and a heat transfer model are introduced tostudy the heating and cooling processes in the HAMR media; then, by integrationof the SPT head and the laser heating source, the recording performance issimulated and investigated on a single track at area density of 1Tb/in2. The mainresults are as follows:1) The cooling process is dominated by heat conduction that transfers heat from the magnetic layer to the soft underlayer, and increasing the thermal conductivityκof the SUL accelerates the heat transfer process, and then leads to a reduction of the local maximum temperature.2) It is found that the written bit pattern in the recording layer is determined not only by the head geometry and the head field, but by the way that the media respond to the laser. The optimum writing temperature is 722K, which is a little lower than the curie temperature of FePt alloy (770K). It should also be noted that, at higher temperature above 722K, bit patterns can not be written properly in the magnetic layer, since the saturation magnetization is nearly zero at the center of the medium.3) In the recording process,the head-medium speed is 35m/s, the bit-aspect radio is 2.7, and the area density is beyond 1Tb/in2. The distance from laser waveguide to rear/front edge of SPT head should be less than 41.4/1.4nm respectively, for a proper write-in.
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