| Summary: | 碩士 === 國立中正大學 === 物理系研究所 === 104 === Applying a longitudinal current in heavy metal, such as Ta or Ru, a spin current is generated along the transverse direction due to the spin Hall effect (SHE). This spin current may further exert a torque on the adjacent ferromagnetic layer and causes a magnetic switching of the ferromagnetic layer.
In this thesis, we fabricated thin film samples of synthetic antiferromagnetic structure: MgO(1)/CoFeB(1.2)/ Ta(x)Ru(1-x)(1)/CoFeB/MgO(1) (1<x<0, unit: nm) and measure the electrical and magnetic properties of these samples. The experimental work is divided into two parts: (1) Investigating the perpendicular magnetic anisotropy of these structures and the exchange coupling between CoFeB layers. (2) Investigating of the current impact of the adjacent ferromagnetic layers by spin Hall effect. The main results are listed as follows:
1. Strong perpendicular magnetic anisotropy (PMA) is observed either x ~ 1 or x ~ 0, which is either on the Ta rich side or Ru rich side. However, when x ~ 0.5, the PMA clearly reduces resulting in a stripe domain structure.
2. The PMA observed in Ta rich side is related to the strong interface anisotropy originated from Fe-O hybridization. However, the PMA at Ru rich side is related to the strong antiferromagnetic interaction originated from the exchange coupling through the Ru spacer.
3. The domain structure is sensitive to the history of the external field and shows strong angular dependence. The analysis of the angular dependence gives rise to a quantitative understanding of the evolution of the domain structure.
4. Both Hall resistance (Rxy) and magnetoresistance (Rxx) are measured for the sample of x = 0.5 (Ta0.5/Ru0.5) and found various magnetoresistance (MR) including anisotropic magnetoresistance (AMR), spin Hall magnetoresistance (SMR) and giant magnetoresistance (GMR).
5. By analyzing both Rxy and Rxx, we are able to map out the average magnetic configuration during the magnetic reversal. These results give rise to a detailed description of the variation of the stripe domain structure which may be useful for the future application on the domain wall motion type magnetic devices.
Key word: Spin Hall Magnetoresistance, synthetic antiferromagnet, CoFeB
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