Interlayer Exchange Coupling In GaAs And GaN-based Diluted Magnetic Semiconductor Multilayers Studied By First-Principles Calculations

The GMR effect has initiated spintronics and with the discovery of diluted magnetic semiconductors a new field of semiconductor spintronics has emerged. Compared to the traditional semiconductor devices, the spin devices have powerful potential values and have more advantages, such as quick working speed, small size, and lower energy consumption. Diluted magnetic semiconductors are important materials for the applications of spintronics devices and recently are becoming a hotspot of materials science.The GMR effect is a magnetoresistance effect observed in the multilayers which are stagger stacked by ferromagnetic and nonmagnetic metallic materials. The Diluted magnetic semiconductors (DMS) have both magnetic property and semiconductor property. Therefore, a lot of detailed works have been done about the interlayer exchange coupling (IEC) in a series diluted magnetic semiconductors multilayers. However, usually, only ferromagnetic IEC was observed in DMS multilayers and only very recently, the antiferromagnetic IEC in Be-doped DMS multilayer systems was reported. In this thesis, we studied the IEC of both Mn doped GaAs-based DMS magnetic multilayers, and Mn and Cu doped GaN-based DMS magnetic multilayers by first-principles calculations.It is found that, the IEC of the multilayers of (Ga,Mn)As is decided by both the thickness of pure GaAs nonmagnetic layers and Be substitutions in GaAs nonmagnetic spacer. For the pure GaAs nonmagnetic layers, the ferromagnetic IEC is always achieved which can be explained by the RKKY interaction with a gap in materials, the calculating result is consistent to the experimental results. The key of the tunable IEC is the s-d interaction, the strong s-d interaction can effectively mediate the spin interaction between the ferromagnetic (Ga, Mn)As layers. From the calculations, we conclude that the carrier plays an important role in the IEC. Moreover, we also study the relationship between the electric field and the IEC and we observe that the IEC shows a periodical variety as the electric field changing.For the Mn and Cu doped GaN-based multilayers systems, with the pure GaN nonmagnetic layers, the ground states are ferromagnetic for two systems which can also be explained by the RKKY interaction with a gap in materials. However, the results are quite different when Mg-doped GaN nonmagnetic spacers. For the (Ga,Mn)N system, the IEC can be transferred from ferromagnetic to antiferromagnetic gradually, with the GaN spacer's thickness increasing. But for the (Ga,Cu)N system, the antiferromagnetic IEC is immediately achieved when two Mg atoms are doped into the interfaces between the (Ga, Cu)N layers and the spacers. The main difference is that the Cu-Mg hybridization has a stronger sp-d hybridization (compared with the Mn-Mg hybridization) around the Fermi energy level. These results indicate that Cu is a better dopant for the device application of the GaN-based DMS magnetic multilayers.