| Summary: | 碩士 === 國立中正大學 === 物理學系暨研究所 === 101 === In this thesis, we study the temperature-dependent magnetic behavior of [MgO/ Co20Fe60B20/Ta/Co20Fe60B20/MgO] and [MgO/Co20Fe60B20/Ru /Co20Fe60B20/MgO], which are either ferromagnetic-coupled or antiferromagnetic-coupled (synthetic ferrimagnet) structure, depending upon the spacer thickness, with perpendicular anisotropy. The experiments were divided into three sections:
1. Ta(10)/MgO(1)/Co20Fe60B20 (1.2)/Ta(1.3)/Co20Fe60B20 (1.2)/MgO(1)/Ta(3), annealed 300 oC, unit : nm
This structure has weak antiferromagnetic coupling ~ 0.02 erg/cm2 between CoFeB layers. Four different magnetic phases are identified as a function of temperature between 10 - 300 K. A singularity of the change of the magnetization is found at ~ 150 K and the origin of the singularity results from the coercivity crossover between the ferromagnetic layers.
2. Ta(10)/MgO(1)/Co20Fe60B20 (1.2)/Ru(0.7)/Co20Fe60B20 (1.2)/MgO(1)/Ta(3), annealed 340 oC, unit : nm
This structure has relatively strong antiferromagnetic coupling ~ 0.5 erg/cm2 between CoFeB layers. Different magnetic phases are also identified as a function of temperature. However, the magnetic phases are very different from structure 1. The low temperature phase especially shows a spin reorientation below T ~ 50K. Form our experimental results, the easy axis seems to shift to the direction off the perpendicular direction. The H-T magnetic phase diagram is discussed.
3. Ta(10)/MgO(1)/Co20Fe60B20 (1.2)/Ru(1.3)/Co20Fe60B20 (1.2)/MgO(1)/Ta(3), annealed 300 oC, unit : nm
This structure has weak ferromagnetic coupling between CoFeB layers. The magnetic hysteresis (M-H) curve at room temperature shows a typical stripe-domain-like characteristic in which the remanence and coercivity both vanish at H ~0. While cooling, the M-H curves recover back to a normal ferromagnetic-coupled states indicating that the anisotropy is dominant at lower temperature.
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