Induced ferromagnetism in Ni(II) doped ZnO monolayers via Al co-doping and their optical characteristics:ab initiostudy.

For applications in magneto-electronic devices, diluted magnetic semiconductors (DMSs) usually exhibit spin-dependent coupling and induced ferromagnetism at high Curie temperatures. The processes behind the behavior of optical emission and ferromagnetism, which can be identified by complicated microstructural and chemical characteristics, are still not well understood. In this study, the impact of Al co-doping on the electronic, optical, and magnetic properties of Ni(II) doped ZnO monolayers has been investigated using first principles calculations. Ferromagnetism in the co-doped monolayer is mainly triggered by the exchange coupling between the electrons provided by Al co-doping and Ni(II)-dstates; therefore, the estimated Curie temperature is greater than room temperature. The spin-spin couplings in mono-doped and co-doped monolayers were explained using the band-coupling mechanism. Based on the optical study, we observed that the Ni-related absorption peak occurred at 2.13-2.17 eV, showing a redshift as Ni concentrations increased. The FM coupling between Ni ions in the co-doped monolayer may be responsible for the reduction in the fundamental band gap seen with Al co-doping. We observed peaks in the near IR and visible regions of the co-doped monolayer, which improve the optoelectronic device's photovoltaic performance. Additionally, the correlation between optical characteristics and spin-spin couplings has been studied. We found that the Ni(II)'sd-dtransition bands or fundamental band gap in the near configuration undergoes a significant shift in response to AFM and FM coupling, whereas in the far configuration, they have a negligible shift due to the paramagnetic behavior of the Ni ions. These findings suggest that the magnetic coupling in DMS may be utilized for controlling the optical characteristics.

Wire coating analysis using Phan-Thien-Tanner fluid subject to Lorentz force as a polymer coating material in a canonical covering die.

Wire coating is widely used for electrical insulation to protect the wire from electric shock, prevent electrical leakage, and ensure that the electrical current flows smoothly. In this investigation, a pressurized coating die is used to explore the PTT fluid as a polymer material for wire in a magnetic field. The flow field, flow rate, temperature profile, thickness of the wire coating, volume flow rate, and shear stress are all given exact solutions. Graphs were used to illustrate the effects of certain important technical parameters, including flow rate, wire coating thickness, shear stress, and pressure gradient. It has been noted that as the values of X, Deborah number, and ratio of radii are improved, the volume and thickness of the coated wire rise. The Deborah number has a higher volume flow than the X and radii ratios. A reference to existing literature is made in order to support the validity of the current study.

Spin-related optical behaviors of dilute magnetic semiconductor ZnSe:Ni(II) nanobelts.

There are varied spin states in dilute magnetic semiconductors, and carriers are not the only elementary excitations that carry the spin. This article reports a study of spin interactions in excitons of ZnSe:NiI(II) nanostructures. High-quality ZnSe:NiI(II) nanobelts (NBs) prepared by chemical vapor deposition show a zinc blende structure by x-ray diffraction and Raman spectroscopy. The temperature-dependent photoluminescence spectra of doped NBs show independent free exciton (FX) and exciton magnetic polaron (EMP) peaks at room temperature with ferromagnetically coupled Ni ions. A single-mode lasing profile was obtained with femtosecond laser excitation due to condensation of EMPs over a threshold. The luminescence lifetimes at different pump powers indicated different relaxation profiles, confirming the formation of coherent EMP aggregates. At a slightly higher dopant concentration, a weak peak at the high-energy side of the FX peak showed up separately at low temperature; this should be the magnetic polaron emission band from the antiferromagnetically coupled Ni(II) pair binding with a FX (antiferromagnetic magnetic polaron). These results illustrate the typical spectroscopic characteristics of spin-spin magnetic coupling, exciton-spin or phonon interactions in dilute magnetic semiconductor nanostructures, showing that their different coupled spin types could work as exciton binders for their collective excitons, with possible use in spin nanophotonic devices and quantum modulations.

Ab initio study of optoelectronic and magnetic properties of Mn-doped ZnS with and without vacancy defects.

The effect of vacancy defects on optoelectronic and magnetic properties of Mn-doped ZnS have been systematically investigated using first principle approaches. A single Mn substitution at Zn site induces a spin-polarized ground state in pure ZnS with total magnetization 5 [Formula: see text]. Our results for magnetic coupling show that the coupling between Mn spins in pure Mn doped ZnS is antiferromagnetic under the super-exchange mechanism. The existence of native defects has a great influence on the magnetic ground state of Mn-doped ZnS. In particular, a p -type defect such as Zn vacancy play a crucial role in stabilizing ferromagnetic ground state while n-type defect, such as S vacancy, has no effect on the magnetic ground state i.e. the interaction between two Mn spins with S-vacancy remain antiferromagnetic. Furthermore, optical properties such as dielectric functions, absorption coeffiecients, reflectivity and transmissitivity for Mn doped systems with and without vacancy defect were also studied, and we found that an absorption peak was obtained in the infrared region which is attributed to the defect states introduced by Zn vacancy in the system. In a S-vacancy defect system, the peaks in the near infrared and visible region are due to donor states introduced by S vacancy defect and these peaks are produced by electrons flipping from a spin up state to a spin down state. Finally, we also correlated the magnetic interactions with the d-d optical transition in pure Mn-doped ZnS and found that the d-d transitions during optical absorptions are red shifted and blue shifted in FM and AFM coupled Mn ions pair, which is in good agreement with the experimental observations. This study may help to understand the behavior of optical and magnetic properties of DMS under vacancy defects.

Optoelectronic and magnetic properties of Mn-doped and Mn-C co-doped Wurtzite ZnS: a first-principles study.

In order to meet the requirement of spintronic and optoelectronic, we have systematically investigated the effect of Mn doping and co-doping of Mn with C on the electronic, magnetic and optical properties of wurtzite zinc sulfide (ZnS) using first principle calculations. Our results find that single Mn doping alters the non-magnetic ZnS to a magnetic one and keeps its semiconducting and a semiconductor to half-metal transition is observed for Mn-C co-doping. Furthermore, an antiferromagnetic (AFM) and ferromagnetic (FM) ground states are favorable for Mn-doped and Mn-C co-doped system, respectively. Additionally, the optical properties of our studied configuration have been calculated in terms of real and imaginary parts of the complex dielectric function, absorption coefficient, and reflectivity. The absorption edge shifts slightly toward lower energy and intensity of the main peak become weak for single Mn doping, and a sharp peak at low energy is observed for the Mn-C co-doping. The analysis of optical absorption of Mn ions doped system shows the blue- and red-shifts of the d-d transition in the AFM and FM coupled of Mn ions doped configuration, respectively which is in good agreement with the experimental observations. The improved magnetic and optical properties of Mn-C co-doped ZnS shed light on the future application of such kind of materials in spintronic and optoelectronic devices such as remote sensing and photovoltaics.