| Summary: | 碩士 === 國立中正大學 === 物理系研究所 === 104 === A series of magnetic multilayered structures are 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(1.3)/W(1)/CoFeB(x)/ MgO(1) /Ta(3), x= 0.9, 1.0,1.1 (units are nanometer). All samples are characterized by vibrating sample magnetometer (VSM) and the one with x= 1.1 is also measured by Hall resistance measurements.
The anomalous Hall resistance (Rxy) measurements include the current scan Rxy(I) and field scan Rxy(H), respectively. Note that the Rxy(I)(Rxy(H)) is measured as function of a fixed field (fixed current) and all these results are then mapped to a comprehensive phase diagram. The main interests focus on the current scan Rxy(I). However, the analysis starts with Rxy(H) because these results provide useful information on the relevant magnetic states which help to for clarify the role of the spin current and symmetry of the trilayered structure.
The experimental results of sample x=1.1 has two parts:
1. The characterization of VSM: the effective film thickness of the top CoFeB is 0.733 nm and bottom CoFeB is 0.526 nm.The total dead layer is 1.111nm.The magnetization of the multilayer is 1369emu/cm3, the anisotropy field is 3900 Oe, and the switching field is 323 Oe
2. The results of anomalous Hall resistance measurements are further divided in to three parts:
A. Rxy(Hz):
We measured Rxy(Hz) in range ±2000 Oe and ±21 mA. The magentic reversal shows parallel state at high field and antiparallel state at low field. However, the magnetic state varies as the current density varies, indicating a strong spin current effect. Basically, the magnetic moments are along the easy axis (z-axis) at lower current density. The magnetic moments tend to tilt to the y-direction as I > 15 mA. However, no spin flop state is observed probably because the relatively high anisotropy energy.
B. Rxy(Hx):
The results of field scan Rxy(Hx) show that the magnetic states change between c-state and inverse c-sate. No obvious spin flop state (v-state) is observed probably because the anisotropy energy is larger than the interlayer exchange energy. Basically, the magnetic moments are confined in the x-z plane at lower current density but the gradually change to be confined in y-z plane at Hx> 15 mA. This indicates that the switch is due to the damping like torque at lower current. However, both field like torque and damping like torque play role on the current induced switching.
C. Rxy(I):
By analyzing the current-field (J-Hx) phase diagram, we estimate the spin Hall angle and effect anisotropy field in the low field region (- 500 Oe < Hx < 500 Oe) and high field region. The effective spin Hall angles in both regions are in the rage of 0.025 – 0.038 and the corresponded anisotropy fields are in the range of 1650 Oe - 2100 Oe. Zero field switching is also observed indicating that the field like torque may initiate the process and break the in-plane symmetry along the x-direction.
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