The Mangetic And Magneto-transport Properties Of CoO_1-v Films And Devices

Electrons have both charge and spin degrees of freedom. The past decades have witnessed remarkable success of semiconductor electronics, whose functionality is essentially realized by the controlled motion of charges. The Moore’s law told us that the number of transistors in a dense integrated circuit doubles approximately every 18 months. This exponential improvement has dramatically enhanced the performance of integrated circuits in semiconductor electronics. However, the growth of the international technology roadmap for semiconductors has slowed down in recent years, for its increasingly higher degree of integration is approaching the physics limit. Semiconductor technology has continuously reduced its working dimension to a nanoscale dimension, where exchange interaction among carriers can no longer be ignored. In order to overcome the limitation of traditional microelectronics, spintronics, which deals with both spin and charge degrees of freedom, offers opportunity for further miniaturization, lower power consumption, and multifunctionality in information storage and communication technology.In the past several decades, the spintronics has developed quickly. With the discovery of GMR, TMR, and SHE, it attracted lots of attention. GMR was observed in thin-film structures composed of alternating ferromagnetic and non-magnetic conductive layers. It comes from the spin dependent scattering in FM/NM/FM structure. While TMR effect was firstly observed in Fe/Ge/Fe junction, which is based on spin dependent tunneling. Besides, magnetic semiconductor, which takes advantage of both spin and charge degrees of freedom within the same materials, becomes one of the most promising materials in the 21th century.Magnetic tunnel junctions (MTJs) have attracted increasing attention due to its high sensitivity to magnetic field, high resistivity, low energy consumption and stability. They were widely used in magnetic storage and magnetic sensor. However, in most of the research, only one important physical properties can realized in a normal MTJ. For example, binary transition metal oxides such as NiO, TiO2, and CoO have been widely studied as memristance materials, but they are seldom used as the insulating layer in MTJs. By contrast, the insulating barrier of MTJs with large TMR is usually limited to very few oxides, such as Ai2O3 and MgO etc, where junction resistance can not be electrically tuned in a reversible way. So, if we can combine memristance and magnetoresistance in one oxide magnetic tunnel junction, a multi-state resistor will be realized.In this letter, we fabricated Co/CoO-ZnO/Co MTJs by magnetron sputtering and shadow mask technique. This structure combines memristance and magnetoresistance together within the CoO-ZnO nano composite barrier layer. The bipolar resistance switching ratio is as high as 90, and the HRS resistance decreases with increasing temperature. This is a typical feature of tunneling transport behavior, and the LRS resistance increases with increasing temperature, showing metallic-like transport behavior. The TMR ratio of HRS gets to 8% at room temperature, which increases to 13.3% at 5K. The bipolar resistance switching can be explained by the metal-insulator transition of CoO1-v layer due to the migration of oxygen ions between CoO-ZnO nano composite barrier layer. XPS results also suggest the existence of CoO. The three resistance states achieved in the MTJ will have potential applications in the future.What’s more, the high coercivity, perpendicular anisotropy, enhanced Kerr rotation and giant exchange anisotropy in the Co-CoO system have attracted lots of attention. In the beginning, experimental and theoretical discussion is based on the fact that Co is a ferromagnetic metal, while stoichiometric CoO is an antiferromagnetic insulator. Later, it is realized that non-stoichiometric defects, such as oxygen vacancies and uncompensated surface spin states could significantly alter the properties. Hence, a systematic investigation of CoO1-v with various oxygen vacancies defects would be a great help to the future practical materials and device design. In this work, we demonstrate that both a metal-insulator transition and a giant exchange bias effect with HE≈4380 Oe and HC≈8500 Oe can be obtained in the CoO1-v amorphous composite films by proper changing the concentration of oxygen vacancies. In addition, the magnetic and magneto-transport properties of CoO1-v films can be tailored by post-thermal annealing. Great tunability accompanied with giant exchange bias, relatively high saturation magnetization and high Curie temperature of CoO1-v composite films should find more applications in future spintronics.