The electronic and magnetic properties of (Mn,C)-codoped ZnO are studied in the Perdew-Burke-Ernzerhof form of generalized gradient approximation of the density functional theory. By investigating five geometrical configurations, we find that Mn doped ZnO exhibits anti-ferromagnetic or spin-glass behaviour, and there are no carriers to mediate the long range ferromagnetic (FM) interaction without acceptor co-doping. We observe that the FM interaction for (Mn,C)-codoped ZnO is due to the hybridization between C 2p and Mn 3d states, which is strong enough to lead to hole-mediated ferromagnetism at room temperature. Meanwhile, We demonstrate that ZnO co-doped with Mn and C has a stable FM ground state and show that the (Mn,C)-codoped ZnO is FM semiconductor with super-high Curie temperature (T C = 5475 K). These results are conducive to the design of dilute magnetic semiconductors with codopants for spintronics applications.
When reinforcement particles of composites are imperfectly bonded to the matrix media, the interfacial effect may significantly change the physical fields and the material overall moduli. In this paper, we first recall a physics-based general isotropic interface model of our companion paper to describe such effects. This model is characterized by both the displacement and normal traction discontinuities across an interface and includes the spring-layer interface model and the coherent interface model as particular cases. The strong and weak governing formulations of composites with arbitrarily shaped imperfect interfaces are provided, and a computational approach is developed in the extended finite element method and level set method context to capture the interfacial discontinuities. To examine the performance and validity of the computational approach, the analytical solution of our previous work is used as a benchmark and several bulk and interface material combinations are considered.It is observed that the slowest convergence rate of our approach is no less than 1.45 for all investigated cases, and that both the predicted displacements and normal tractions are in excellent agreement with the analytic solutions. Finally, the influences of material compositions and periodic boundary conditions are evaluated numerically and discussed with a heterogeneous material containing multiple particles.
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