The spin Hall effect has been attracting worldwide attention as one of the methods for controlling the magnetic spin structure. However, it has the limitations in layered structure and requirement of high current density, Jc ~ 10^10A/m2. In this thesis, the Co0.7-Ni0.3-O-Pt phase alloy single layer having a structure in which each phase is randomly distributed in several nanometer sizes like the alloy was reported. Unlike general layered thin film system, this structure has a unique interfacial structure as Co, Ni, O and Pt phases are randomly distributed in a single layer. When a current is applied to this thin film, the spin Hall effect generated by the current flowing through the Pt phases applies spin torque to other phases at the interface, and this result was observed through the change of the exchange bias. To find out the cause of the occurrence, the same structure was fabricated using Au instead of Pt and Fe instead of Co and Ni, and the same experiment was performed. As a result, it was found that the spin structure of the antiferromagnetic material was controlled by the spin Hall effect. In addition, the magnitude of the induced exchange bias was proportional to the current density and degree of oxidation of the film and exhibited stable reversibility and repeatability within the measured current density range. Using this, field-free magnetization switching was also performed and all of the results were achieved at a current density of Jc ~10^10A/m2, which is one order lower than the previously reported value. Therefore, the results of this thesis overcome the limitations of the spin torque and the layered thin film system through phase alloy single layer structure, which suggests the possibility of improving the performance of a device designed based on the control of the spin structure.
Table Of Contents
List of Contents
Abstract i List of contents ii List of tables iv List of figures V
Ⅰ. Introduction 1 ⅠⅠ. Theoretical Background 3 2.1 Magnetism 3 2.1.1 Ferromagnetism 3 2.1.2 Antiferromagnetism 6 2.2 Exchange interaction 8 2.3 Exchange bias 9 2.4 Spin-orbit interaction 11 2.5 Spin Hall effect 13 2.6 Spin torque 16 ⅠⅠⅠ. Experimental Details 18 3.1 Fabrication Co0.7-Ni0.3-O-Pt Phase alloy single layer 18 3.1.1 Metal-metal oxide phase mixture 18 3.1.2 Reactive magnetron co-sputtering 20 3.1.3 Photolithography 23 3.2 Structural property measurement 25 3.2.1 X-ray Diffraction(XRD) 25 3.2.2 Transmission Electron Microscopy(TEM) 26 3.2.3 Scanning Electron Microscope(SEM) 27 3.3 Magnetic property measurement 28 3.3.1 Vibrating Sample Magnetometer(VSM) 28 3.3.2 Magneto-Optical Kerr Effect microscopy(MOKE) 29 IV. Results and Discussion 31 4.1 Characterization of Co0.7-Ni0.3-O-Pt phase alloy single layer 31 4.1.1 Confirm the degree of oxidation 31 4.1.2 Crystal structure of Co0.7-Ni0.3-O-Pt depending on degree of oxidation 33 4.2 Controlled magnetic properties by spin Hall effect 39 4.2.1 Aligned AFM and interface effect through spin Hall effect 39 4.2.2 Magnitude of induced exchange bias depending on oxidation degree and current density 44 4.2.3 Reversible and repeatable exchange bias depending on direction of charge current 46 4.2.4 Field-free magnetization switching 50 V. Conclusion 52 VI. Reference 53