Magnetic Spin Valve And Tunnel Junction Preparation And Performance

Currently, research on spintronics is fast developing due to its widely practical applications. In this thesis, we studied three important contents in spintronics: spin valve, magnetic tunnel junction and exchange bias effect. The main work includes the proposition of L1₀ FePt pinned spin valve, the fabrication of high-quality MgO magnetic tunnel junction, and the investigation of "double shift" effect in the [Co/Ni]/FeMn exchange bias system.The main contents of the thesis are as follows:Chapter 1 introduced the basic theories in spintroniscs as well as the principles, structures, materials and applications of spin valve and magnetic tunnel junction. Chapter 2 introduced the fabrication and calibration of the samples.In Chapter 3, we designed a new kind of spin valve using L1₀ ordered FePt as the pinning layer. In this special spin valve structure, a synthetic antiferromagnetic structure FePt/CoFe/Ru/CoFe is applied. The switching filed of reference layer is about 1.8 kOe, which is much larger than the one in conventional MnIr spin valves with the same pinning structure. And the GMR signal of our FePt spin valve is about 7.04%, comparable to the value of MnIr spin valve.In Chapter 4, we succeeded in the fabrication of high-quality MgO magnetic tunnel junction. In our full structure MgO junction, the room temperature TMR signal is as high as 188%. And in pseudo MgO junction, this value even exceeds 245%. Moreover, in one sample with over 60 junctions, the standard deviation of TMR signal is less than 15%. The bias voltage when TMR signal decreases to half of its maximum (V_half) is around 560 mV. These data indicate our MgO junctions have good uniformity, high TMR signal, and can be used in a wide range of bias voltage.In Chapter 5, we studied an interesting effect called "double shift" in antiferromagnetic exchange bias system. In our exchange bias system, the antiferromagnetic layer is FeMn, and the ferromagnetic layer is [Co/Ni] multilayer with perpendicular magnetic anisotropy. After investigating the conditions where "double shift" effect appears, we discussed the possible reason of it. We believe "double shift" effect is established during the deposition of FeMn layer. It is caused by the random distribution of magnetization direction in as deposited [Co/Ni] multilayer domains. This analysis is proved by a series of experiments in the end of this chapter.Chapter 6 is the summarization and prospect of this work.