Current-Induced Magnetic Phase Transitions and the Critical Current of Perpendicular Synthetic Antiferromagnets

• Main Authors: CHEN,LIANG-YU, 陳亮宇
• Other Authors: CHERN,GUNG
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/3zbkj5

碩士 === 國立中正大學 === 物理系研究所 === 106 === Spin current generated by the spin Hall effect in a heavy metal that would diffuse up and down to adjacent ferromagnetic layers and exert torque on their magnetization is called spin-orbit torque. The torque causes a magnetic switching of the ferromagnetic layer. A magnetic multilayered structures is fabricated by sputtering and the current induced magnetization switching by spin Hall effect is studied in this thesis.The samples include: Si(substrate)/ Ta(10)/ MgO(1)/ CoFeB(1.4)/ Ru(2.2)/ CoFeB(1.0) / MgO(1) / Ta(3) (unit : nanometer). The sample is characterized by vibrating sample magnetometer (VSM) and measured by Hall resistance measurements. The results are divided into two parts: VSM & Hall resistance measurement. 1.The characterization of VSM: the effective film thickness of the top CoFeB is 0.678nm and bottom CoFeB is 0.663 nm.The total dead layer thickness is 1.039 nm.The magnetization of the multilayer is 1312.5 emu/cm3, the anisotropy field is 2551 Oe, and the switching field is 606 Oe. 2. The results of anomalous Hall resistance measurements are further divided in to three parts: A.Rxy(Hz): The comparison of the Rxy(Hz) curve with the M(H) curve shows a significant change, which indicates the induced current effect due to spin current. The M(H) curve shows that the remanence of antiferromagnetic state (A-state) is near zero ,but the Rxy(Hz) results vary with magnetic field. This current effect induced the magnetic state switching and magnetic moment canting. Applying current higher than 18mA the range of A-state vanish. And the magnetic state also transforms from the A-state into the spin flop state (v-state) . In addition, it reaches a critical point in the current field (Hz, I) diagram. At the critical point the magnetic state transformsfrom the A-state into the V-state.   B.Rxy(Hx): The current effect induced positive and negative A-state switching by applying magnetic field Hx. And applying more current the critical phenomena also appear. The switching current density in Rxy(Hx) as a function of the Hx is mapped out in a current field (Hx, I) diagram. The diagram is qualitatively similar to (Hz) in which the magnetic states change significantly as current > 17mA. C.Rxy(I) : Rxy(I) measures the anomalous Hall resistance by current scan from 20 mA to – 20 mA with a fixed Hx. The critical current is mapped out as a function of Hx and form a (I, Hx) diagram. We found that the diagram may be divided into a inner region (-100 Oe < Hx < – 100 Oe) and outer region elsewhere within the range of 500 Oe. The switching current in the inner region is more than critical current defined by Hz、Hx. That shows the in-plan symmetry breaking of the magnetic states due to the critical current.