| Spintronics established a link between spin properties and charge properties, the combination of these two degrees of freedom provides a wider space for the development of electronic devices with excellent performance. Racetrack memory, spin transfer nano-oscillator and STT-MRAM are three typical spintronics devices, which have huge application prospects. However, there are still some bottleneck problems to be settled before the application. By micromagnetic simulation and experiment, this thesis try to improve the performance of racetrack memory and spin transfer nano-oscillator.(1) Racetrack memoryThe first racetrack memory proposed by Parkin is based on 180 o domain wall(180DW). However, devices that based on 360 o domain wall(360DW) not only have higher storage density but also have remarkable ability to resist magnetic interfering field. In the third chapter, we proposed a simple injection line to generate 360 DWs. Simulations showed that, to generate a 360 DW, current pulse should decrease slowly. Then a coupled DW system between a 180 DW and a 360 DW, or two 360 DWs in two parallel nanowires are presented to enhance the stability of 360 DW. The maximum critical velocity of such system is 81.1 % larger than that of a single 360 DW.In the fourth chapter, we investigated the interaction between propagating spin wave(or magnonic) and a 360 DW in a nanostrip. There is no charge transport in the spin wave propagating process, which might provide a new approach to solve the Joule heating problem. It is found that propagating spin wave can also drive a 360 DW motion, the velocity and direction are closely related to the material parameters and the frequency of spin wave. Moreover, when the spin wave is reflected from the moving 360 DW, we observed the Doppler effect clearly. After passing through a 360 DW, the phase of the spin wave is changed.The DW in perpendicular magnetic anisotropy(PMA) nanowire is very narrow, and the critical current density is lower than that of in-plane magnetic anisotropy system. Thus, racetrack memory based on PMA nanowire could improve the storage density and reduce the power consumption. For the memory devices research, it is important to first optimize the injection of a DW into the nanowire. Conventionally, DW injection is achieved by applying an electrical current via a thick and conductive stripline deposited on top of the magnetic nanowire. In the fifth chapter, we demonstrate an energy efficient structure to inject DWs. Our measurements show that the Π-shaped stripline can deterministically write a magnetic data bit in 15 ns even with a relatively low current density of 5.34×1011 A/m2. Both experimental and simulation results show that our design consumes about 30% of the energy required by conventional injection designs. At last, we studied the pinning and depinning effect of DW at the cross structure.(2) Spin transfer nano-oscillatorSpin transfer nano-oscillator shows a lot of outstanding performance. However, there remain several critical problems yet to be resolved, in particular, the low microwave power of a single STNO. A good approach to solve this problem is nano-oscillator array. In the sixth chapter, the oscillation behavior of a magnetic skyrmion induced by spin polarized current in MTJ nanodisk is investigated. According to this phenomenon, we propose a new kind of spin transfer nano-oscillator that based on multiple skyrmions. The linewidth can be smaller than 1MHz, which offers a huge advantage for STNO applications. Morever, this device can work at a current density magnitude of 108 A/m2 and the range of working frequency is hugely extended, the minimum working frequency can be close to 0 MHz and the maximum is about gigahertz. |
PDF Full Text Request