The Micromagnetic Study Of Material And Device In Energy Assisted Magnetic Recording

The magnetic recording system up to date utilizes the ferromagnetic properties of materials to write, read and store information. Energy assisted magnetic recording（EAMR） has been proposed to overcome the writability issues. Microwave assisted magnetic recording（MAMR） and h eat assisted magnetic recording（HAMR） are two kinds of EAMR technologies to achieve extremely high density above 4Tb/in2. In this thesis, micromagnetic model with the spin transfer torque（STT） term included are built for perpendicular spin torque oscillator（STO） which is the center part in the head of MAMR. The oscillation properties and switching dynamics of single STO under different current densities and external fields are studied. Furthermore, oscillation properties of STO pair coupled by m agnetostatic interaction are studied. In addition, the lattice vibration properties of L1₀-Fe Pt which is the most important recording media material in the HAMR system are studied by molecular dynamic（MD） and lattice dynamic（LD） methods.The state diagram of perpendicular STO is studied by macrospin model and micromagnetic model. The state diagrams of current, external field and external field angle are calculated. Different oscillation states are found in frequency state diagrams. The frequency saturation and discrete saturation frequencies are found caused by the finite in-plane sizes of the pillar and spatially nonuniform magnetization configuration. The simulation shows that the oscillation could be controlled by current density combined with external field and saturation magnetization of field generation layer（FGL） so as to achieve a wide frequency range. An optimized current and applied field region is given for MAMR, considering both frequency and output field oscillation amplitude.The switching dynamics of the STO with Co/Pt perpendicular anisotropy reference layer（REF） and in-plane anisotropy FGL is studied. The interfacial anisotropy of the Co/Pt REF is correlated to the thickness of Co layer; therefore, four samples of REF with 0.3nm, 0.4nm, 1nm and 2nm thick Co are utilized for the dynamic study of STO. It is found that the STO with 1nm Co has optimum switching performance in a 10 k Oe alternative field（from the main pole of writer）, where the REF and the FGL flip coherently within 0.3ns. In addition, the switching dynamics of STO with different saturation magnetization and interfacial anisotropy REF are compared. In the optimized samples, it is found that REF switching is assisted by the FGL microwave field after the FGL chirality changes.The state diagram of magnetostatic coupling phase-locked STO is studied by the macrospin model and micromagnetic simulation. The state diagrams of current density and external field are calculated. The simulation shows that there are two phase-lock current density regions. In low current Region I the magnetization configuration of FGL is uniform; in high current Region II, the magnetization configuration of FGL is highly nonuniform. The phase-lock range dependence on external field is complicated, possibly caused by the strong coupling between two STOs. In addition, the results of di fferent STOs separation are compared, which shows the effect of strong coupling between two STOs.LD is utilized to calculate the phonon spectrum of L1₀-Fe Pt crystal; and MD method is constructed to calculate the phonon density of state（PDOS）, which can be compared to the result of LD. By the phonon spectrum and PDOS, the optimum mode and frequency of the laser to activate phonons is found in L1₀-Fe Pt, and the heating rate using different frequency a nd mode of the laser has been schematically simulated by MD method.